HDFS-10687. Federation Membership State Store internal API. Contributed by Jason Kace and Inigo Goiri.

(cherry picked from commit 95cae08849d23cf12c5d280c29f90908e6a90d40)

hadoop-hdfs-project/hadoop-hdfs/dev-support/findbugsExcludeFile.xml

@@ -14,6 +14,9 @@
      <Match>
        <Package name="org.apache.hadoop.hdfs.qjournal.protocol" />
      </Match>
+     <Match>
+       <Package name="org.apache.hadoop.hdfs.federation.protocol.proto" />
+     </Match>
      <Match>
        <Bug pattern="EI_EXPOSE_REP" />
      </Match>

hadoop-hdfs-project/hadoop-hdfs/pom.xml

@@ -331,6 +331,7 @@ http://maven.apache.org/xsd/maven-4.0.0.xsd">
                   <include>QJournalProtocol.proto</include>
                   <include>editlog.proto</include>
                   <include>fsimage.proto</include>
+                  <include>FederationProtocol.proto</include>
                 </includes>
               </source>
             </configuration>

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -27,6 +27,8 @@
 import org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault;
 import org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyRackFaultTolerant;
 import org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.RamDiskReplicaLruTracker;
+import org.apache.hadoop.hdfs.server.federation.resolver.ActiveNamenodeResolver;
+import org.apache.hadoop.hdfs.server.federation.resolver.MembershipNamenodeResolver;
 import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreDriver;
 import org.apache.hadoop.hdfs.server.federation.store.driver.impl.StateStoreFileImpl;
 import org.apache.hadoop.hdfs.server.federation.store.driver.impl.StateStoreSerializerPBImpl;
@@ -1169,8 +1171,9 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
       "org.apache.hadoop.hdfs.server.federation.MockResolver";
   public static final String FEDERATION_NAMENODE_RESOLVER_CLIENT_CLASS =
       FEDERATION_ROUTER_PREFIX + "namenode.resolver.client.class";
-  public static final String FEDERATION_NAMENODE_RESOLVER_CLIENT_CLASS_DEFAULT =
-      "org.apache.hadoop.hdfs.server.federation.MockResolver";
+  public static final Class<? extends ActiveNamenodeResolver>
+      FEDERATION_NAMENODE_RESOLVER_CLIENT_CLASS_DEFAULT =
+          MembershipNamenodeResolver.class;
 
   // HDFS Router-based federation State Store
   public static final String FEDERATION_STORE_PREFIX =
@@ -1192,6 +1195,16 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final long FEDERATION_STORE_CONNECTION_TEST_MS_DEFAULT =
       TimeUnit.MINUTES.toMillis(1);
 
+  public static final String DFS_ROUTER_CACHE_TIME_TO_LIVE_MS =
+      FEDERATION_ROUTER_PREFIX + "cache.ttl";
+  public static final long DFS_ROUTER_CACHE_TIME_TO_LIVE_MS_DEFAULT =
+      TimeUnit.MINUTES.toMillis(1);
+
+  public static final String FEDERATION_STORE_MEMBERSHIP_EXPIRATION_MS =
+      FEDERATION_STORE_PREFIX + "membership.expiration";
+  public static final long FEDERATION_STORE_MEMBERSHIP_EXPIRATION_MS_DEFAULT =
+      TimeUnit.MINUTES.toMillis(5);
+
   // dfs.client.retry confs are moved to HdfsClientConfigKeys.Retry 
   @Deprecated
   public static final String  DFS_CLIENT_RETRY_POLICY_ENABLED_KEY

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/MembershipNamenodeResolver.java

@@ -0,0 +1,290 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.resolver;
+
+import static org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState.ACTIVE;
+import static org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState.EXPIRED;
+import static org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState.UNAVAILABLE;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.server.federation.store.MembershipStore;
+import org.apache.hadoop.hdfs.server.federation.store.StateStoreCache;
+import org.apache.hadoop.hdfs.server.federation.store.StateStoreService;
+import org.apache.hadoop.hdfs.server.federation.store.StateStoreUnavailableException;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamenodeRegistrationsRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamenodeRegistrationsResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamespaceInfoRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamespaceInfoResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.NamenodeHeartbeatRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateNamenodeRegistrationRequest;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+import org.apache.hadoop.util.Time;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Implements a cached lookup of the most recently active namenode for a
+ * particular nameservice. Relies on the {@link StateStoreService} to
+ * discover available nameservices and namenodes.
+ */
+public class MembershipNamenodeResolver
+    implements ActiveNamenodeResolver, StateStoreCache {
+
+  private static final Logger LOG =
+      LoggerFactory.getLogger(MembershipNamenodeResolver.class);
+
+  /** Reference to the State Store. */
+  private final StateStoreService stateStore;
+  /** Membership State Store interface. */
+  private final MembershipStore membershipInterface;
+
+  /** Parent router ID. */
+  private String routerId;
+
+  /** Cached lookup of NN for nameservice. Invalidated on cache refresh. */
+  private Map<String, List<? extends FederationNamenodeContext>> cacheNS;
+  /** Cached lookup of NN for block pool. Invalidated on cache refresh. */
+  private Map<String, List<? extends FederationNamenodeContext>> cacheBP;
+
+
+  public MembershipNamenodeResolver(
+      Configuration conf, StateStoreService store) throws IOException {
+    this.stateStore = store;
+
+    this.cacheNS = new ConcurrentHashMap<>();
+    this.cacheBP = new ConcurrentHashMap<>();
+
+    if (this.stateStore != null) {
+      // Request cache updates from the state store
+      this.stateStore.registerCacheExternal(this);
+
+      // Initialize the interface to get the membership
+      this.membershipInterface = this.stateStore.getRegisteredRecordStore(
+          MembershipStore.class);
+    } else {
+      this.membershipInterface = null;
+    }
+
+    if (this.membershipInterface == null) {
+      throw new IOException("State Store does not have an interface for " +
+          MembershipStore.class.getSimpleName());
+    }
+  }
+
+  @Override
+  public boolean loadCache(boolean force) {
+    // Our cache depends on the store, update it first
+    try {
+      this.membershipInterface.loadCache(force);
+    } catch (IOException e) {
+      LOG.error("Cannot update membership from the State Store", e);
+    }
+
+    // Force refresh of active NN cache
+    cacheBP.clear();
+    cacheNS.clear();
+    return true;
+  }
+
+  @Override
+  public void updateActiveNamenode(
+      final String nsId, final InetSocketAddress address) throws IOException {
+
+    // Called when we have an RPC miss and successful hit on an alternate NN.
+    // Temporarily update our cache, it will be overwritten on the next update.
+    try {
+      MembershipState partial = MembershipState.newInstance();
+      String rpcAddress = address.getHostName() + ":" + address.getPort();
+      partial.setRpcAddress(rpcAddress);
+      partial.setNameserviceId(nsId);
+
+      GetNamenodeRegistrationsRequest request =
+          GetNamenodeRegistrationsRequest.newInstance(partial);
+
+      GetNamenodeRegistrationsResponse response =
+          this.membershipInterface.getNamenodeRegistrations(request);
+      List<MembershipState> records = response.getNamenodeMemberships();
+
+      if (records != null && records.size() == 1) {
+        MembershipState record = records.get(0);
+        UpdateNamenodeRegistrationRequest updateRequest =
+            UpdateNamenodeRegistrationRequest.newInstance(
+                record.getNameserviceId(), record.getNamenodeId(), ACTIVE);
+        this.membershipInterface.updateNamenodeRegistration(updateRequest);
+      }
+    } catch (StateStoreUnavailableException e) {
+      LOG.error("Cannot update {} as active, State Store unavailable", address);
+    }
+  }
+
+  @Override
+  public List<? extends FederationNamenodeContext> getNamenodesForNameserviceId(
+      final String nsId) throws IOException {
+
+    List<? extends FederationNamenodeContext> ret = cacheNS.get(nsId);
+    if (ret == null) {
+      try {
+        MembershipState partial = MembershipState.newInstance();
+        partial.setNameserviceId(nsId);
+        GetNamenodeRegistrationsRequest request =
+            GetNamenodeRegistrationsRequest.newInstance(partial);
+
+        final List<MembershipState> result =
+            getRecentRegistrationForQuery(request, true, false);
+        if (result == null || result.isEmpty()) {
+          LOG.error("Cannot locate eligible NNs for {}", nsId);
+          return null;
+        } else {
+          cacheNS.put(nsId, result);
+          ret = result;
+        }
+      } catch (StateStoreUnavailableException e) {
+        LOG.error("Cannot get active NN for {}, State Store unavailable", nsId);
+      }
+    }
+    if (ret == null) {
+      return null;
+    }
+    return Collections.unmodifiableList(ret);
+  }
+
+  @Override
+  public List<? extends FederationNamenodeContext> getNamenodesForBlockPoolId(
+      final String bpId) throws IOException {
+
+    List<? extends FederationNamenodeContext> ret = cacheBP.get(bpId);
+    if (ret == null) {
+      try {
+        MembershipState partial = MembershipState.newInstance();
+        partial.setBlockPoolId(bpId);
+        GetNamenodeRegistrationsRequest request =
+            GetNamenodeRegistrationsRequest.newInstance(partial);
+
+        final List<MembershipState> result =
+            getRecentRegistrationForQuery(request, true, false);
+        if (result == null || result.isEmpty()) {
+          LOG.error("Cannot locate eligible NNs for {}", bpId);
+        } else {
+          cacheBP.put(bpId, result);
+          ret = result;
+        }
+      } catch (StateStoreUnavailableException e) {
+        LOG.error("Cannot get active NN for {}, State Store unavailable", bpId);
+        return null;
+      }
+    }
+    if (ret == null) {
+      return null;
+    }
+    return Collections.unmodifiableList(ret);
+  }
+
+  @Override
+  public boolean registerNamenode(NamenodeStatusReport report)
+      throws IOException {
+
+    if (this.routerId == null) {
+      LOG.warn("Cannot register namenode, router ID is not known {}", report);
+      return false;
+    }
+
+    MembershipState record = MembershipState.newInstance(
+        routerId, report.getNameserviceId(), report.getNamenodeId(),
+        report.getClusterId(), report.getBlockPoolId(), report.getRpcAddress(),
+        report.getServiceAddress(), report.getLifelineAddress(),
+        report.getWebAddress(), report.getState(), report.getSafemode());
+
+    if (report.getState() != UNAVAILABLE) {
+      // Set/update our last contact time
+      record.setLastContact(Time.now());
+    }
+
+    NamenodeHeartbeatRequest request = NamenodeHeartbeatRequest.newInstance();
+    request.setNamenodeMembership(record);
+    return this.membershipInterface.namenodeHeartbeat(request).getResult();
+  }
+
+  @Override
+  public Set<FederationNamespaceInfo> getNamespaces() throws IOException {
+    GetNamespaceInfoRequest request = GetNamespaceInfoRequest.newInstance();
+    GetNamespaceInfoResponse response =
+        this.membershipInterface.getNamespaceInfo(request);
+    return response.getNamespaceInfo();
+  }
+
+  /**
+   * Picks the most relevant record registration that matches the query. Return
+   * registrations matching the query in this preference: 1) Most recently
+   * updated ACTIVE registration 2) Most recently updated STANDBY registration
+   * (if showStandby) 3) Most recently updated UNAVAILABLE registration (if
+   * showUnavailable). EXPIRED registrations are ignored.
+   *
+   * @param query The select query for NN registrations.
+   * @param excludes List of NNs to exclude from matching results.
+   * @param addUnavailable include UNAVAILABLE registrations.
+   * @param addExpired include EXPIRED registrations.
+   * @return List of memberships or null if no registrations that
+   *         both match the query AND the selected states.
+   * @throws IOException
+   */
+  private List<MembershipState> getRecentRegistrationForQuery(
+      GetNamenodeRegistrationsRequest request, boolean addUnavailable,
+      boolean addExpired) throws IOException {
+
+    // Retrieve a list of all registrations that match this query.
+    // This may include all NN records for a namespace/blockpool, including
+    // duplicate records for the same NN from different routers.
+    GetNamenodeRegistrationsResponse response =
+        this.membershipInterface.getNamenodeRegistrations(request);
+
+    List<MembershipState> memberships = response.getNamenodeMemberships();
+    if (!addExpired || !addUnavailable) {
+      Iterator<MembershipState> iterator = memberships.iterator();
+      while (iterator.hasNext()) {
+        MembershipState membership = iterator.next();
+        if (membership.getState() == EXPIRED && !addExpired) {
+          iterator.remove();
+        } else if (membership.getState() == UNAVAILABLE && !addUnavailable) {
+          iterator.remove();
+        }
+      }
+    }
+
+    List<MembershipState> priorityList = new ArrayList<>();
+    priorityList.addAll(memberships);
+    Collections.sort(priorityList, new NamenodePriorityComparator());
+
+    LOG.debug("Selected most recent NN {} for query", priorityList);
+    return priorityList;
+  }
+
+  @Override
+  public void setRouterId(String router) {
+    this.routerId = router;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/router/FederationUtil.java

@@ -19,25 +19,56 @@
 
 import java.lang.reflect.Constructor;
 
-import org.apache.commons.logging.Log;
-import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.server.federation.resolver.ActiveNamenodeResolver;
 import org.apache.hadoop.hdfs.server.federation.resolver.FileSubclusterResolver;
 import org.apache.hadoop.hdfs.server.federation.store.StateStoreService;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * Utilities for managing HDFS federation.
  */
 public final class FederationUtil {
 
-  private static final Log LOG = LogFactory.getLog(FederationUtil.class);
+  private static final Logger LOG =
+      LoggerFactory.getLogger(FederationUtil.class);
 
   private FederationUtil() {
     // Utility Class
   }
 
+  /**
+   * Create an instance of an interface with a constructor using a context.
+   *
+   * @param conf Configuration for the class names.
+   * @param context Context object to pass to the instance.
+   * @param contextClass Type of the context passed to the constructor.
+   * @param clazz Class of the object to return.
+   * @return New instance of the specified class that implements the desired
+   *         interface and a single parameter constructor containing a
+   *         StateStore reference.
+   */
+  private static <T, R> T newInstance(final Configuration conf,
+      final R context, final Class<R> contextClass, final Class<T> clazz) {
+    try {
+      if (contextClass == null) {
+        // Default constructor if no context
+        Constructor<T> constructor = clazz.getConstructor();
+        return constructor.newInstance();
+      } else {
+        // Constructor with context
+        Constructor<T> constructor = clazz.getConstructor(
+            Configuration.class, contextClass);
+        return constructor.newInstance(conf, context);
+      }
+    } catch (ReflectiveOperationException e) {
+      LOG.error("Could not instantiate: {}", clazz.getSimpleName(), e);
+      return null;
+    }
+  }
+
   /**
    * Create an instance of an interface with a constructor using a state store
    * constructor.
@@ -105,13 +136,14 @@ public static FileSubclusterResolver newFileSubclusterResolver(
    *
    * @param conf Configuration that defines the namenode resolver class.
    * @param obj Context object passed to class constructor.
-   * @return ActiveNamenodeResolver
+   * @return New active namenode resolver.
    */
   public static ActiveNamenodeResolver newActiveNamenodeResolver(
       Configuration conf, StateStoreService stateStore) {
-    return newInstance(conf, stateStore, StateStoreService.class,
+    Class<? extends ActiveNamenodeResolver> clazz = conf.getClass(
         DFSConfigKeys.FEDERATION_NAMENODE_RESOLVER_CLIENT_CLASS,
         DFSConfigKeys.FEDERATION_NAMENODE_RESOLVER_CLIENT_CLASS_DEFAULT,
         ActiveNamenodeResolver.class);
+    return newInstance(conf, stateStore, StateStoreService.class, clazz);
   }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/CachedRecordStore.java

@@ -0,0 +1,237 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreDriver;
+import org.apache.hadoop.hdfs.server.federation.store.records.BaseRecord;
+import org.apache.hadoop.hdfs.server.federation.store.records.QueryResult;
+import org.apache.hadoop.util.Time;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Record store that takes care of caching the records in memory.
+ *
+ * @param <R> Record to store by this interface.
+ */
+public abstract class CachedRecordStore<R extends BaseRecord>
+    extends RecordStore<R> implements StateStoreCache {
+
+  private static final Logger LOG =
+      LoggerFactory.getLogger(CachedRecordStore.class);
+
+
+  /** Prevent loading the cache more than once every 500 ms. */
+  private static final long MIN_UPDATE_MS = 500;
+
+
+  /** Cached entries. */
+  private List<R> records = new ArrayList<>();
+
+  /** Time stamp of the cached entries. */
+  private long timestamp = -1;
+
+  /** If the cache is initialized. */
+  private boolean initialized = false;
+
+  /** Last time the cache was updated. */
+  private long lastUpdate = -1;
+
+  /** Lock to access the memory cache. */
+  private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
+  private final Lock readLock = readWriteLock.readLock();
+  private final Lock writeLock = readWriteLock.writeLock();
+
+  /** If it should override the expired values when loading the cache. */
+  private boolean override = false;
+
+
+  /**
+   * Create a new cached record store.
+   *
+   * @param clazz Class of the record to store.
+   * @param driver State Store driver.
+   */
+  protected CachedRecordStore(Class<R> clazz, StateStoreDriver driver) {
+    this(clazz, driver, false);
+  }
+
+  /**
+   * Create a new cached record store.
+   *
+   * @param clazz Class of the record to store.
+   * @param driver State Store driver.
+   * @param override If the entries should be override if they expire
+   */
+  protected CachedRecordStore(
+      Class<R> clazz, StateStoreDriver driver, boolean over) {
+    super(clazz, driver);
+
+    this.override = over;
+  }
+
+  /**
+   * Check that the cache of the State Store information is available.
+   *
+   * @throws StateStoreUnavailableException If the cache is not initialized.
+   */
+  private void checkCacheAvailable() throws StateStoreUnavailableException {
+    if (!this.initialized) {
+      throw new StateStoreUnavailableException(
+          "Cached State Store not initialized, " +
+          getRecordClass().getSimpleName() + " records not valid");
+    }
+  }
+
+  @Override
+  public boolean loadCache(boolean force) throws IOException {
+    // Prevent loading the cache too frequently
+    if (force || isUpdateTime()) {
+      List<R> newRecords = null;
+      long t = -1;
+      try {
+        QueryResult<R> result = getDriver().get(getRecordClass());
+        newRecords = result.getRecords();
+        t = result.getTimestamp();
+
+        // If we have any expired record, update the State Store
+        if (this.override) {
+          overrideExpiredRecords(result);
+        }
+      } catch (IOException e) {
+        LOG.error("Cannot get \"{}\" records from the State Store",
+            getRecordClass().getSimpleName());
+        this.initialized = false;
+        return false;
+      }
+
+      // Update cache atomically
+      writeLock.lock();
+      try {
+        this.records.clear();
+        this.records.addAll(newRecords);
+        this.timestamp = t;
+        this.initialized = true;
+      } finally {
+        writeLock.unlock();
+      }
+
+      lastUpdate = Time.monotonicNow();
+    }
+    return true;
+  }
+
+  /**
+   * Check if it's time to update the cache. Update it it was never updated.
+   *
+   * @return If it's time to update this cache.
+   */
+  private boolean isUpdateTime() {
+    return Time.monotonicNow() - lastUpdate > MIN_UPDATE_MS;
+  }
+
+  /**
+   * Updates the state store with any record overrides we detected, such as an
+   * expired state.
+   *
+   * @param query RecordQueryResult containing the data to be inspected.
+   * @param clazz Type of objects contained in the query.
+   * @throws IOException
+   */
+  public void overrideExpiredRecords(QueryResult<R> query) throws IOException {
+    List<R> commitRecords = new ArrayList<>();
+    List<R> newRecords = query.getRecords();
+    long currentDriverTime = query.getTimestamp();
+    if (newRecords == null || currentDriverTime <= 0) {
+      LOG.error("Cannot check overrides for record");
+      return;
+    }
+    for (R record : newRecords) {
+      if (record.checkExpired(currentDriverTime)) {
+        String recordName = StateStoreUtils.getRecordName(record.getClass());
+        LOG.info("Override State Store record {}: {}", recordName, record);
+        commitRecords.add(record);
+      }
+    }
+    if (commitRecords.size() > 0) {
+      getDriver().putAll(commitRecords, true, false);
+    }
+  }
+
+  /**
+   * Updates the state store with any record overrides we detected, such as an
+   * expired state.
+   *
+   * @param driver State store driver for the data store.
+   * @param record Record record to be updated.
+   * @param clazz Type of data record.
+   * @throws IOException
+   */
+  public void overrideExpiredRecord(R record) throws IOException {
+    List<R> newRecords = Collections.singletonList(record);
+    long time = getDriver().getTime();
+    QueryResult<R> query = new QueryResult<>(newRecords, time);
+    overrideExpiredRecords(query);
+  }
+
+  /**
+   * Get all the cached records.
+   *
+   * @return Copy of the cached records.
+   * @throws StateStoreUnavailableException If the State store is not available.
+   */
+  public List<R> getCachedRecords() throws StateStoreUnavailableException {
+    checkCacheAvailable();
+
+    List<R> ret = new LinkedList<R>();
+    this.readLock.lock();
+    try {
+      ret.addAll(this.records);
+    } finally {
+      this.readLock.unlock();
+    }
+    return ret;
+  }
+
+  /**
+   * Get all the cached records and the time stamp of the cache.
+   *
+   * @return Copy of the cached records and the time stamp.
+   * @throws StateStoreUnavailableException If the State store is not available.
+   */
+  protected QueryResult<R> getCachedRecordsAndTimeStamp()
+      throws StateStoreUnavailableException {
+    checkCacheAvailable();
+
+    this.readLock.lock();
+    try {
+      return new QueryResult<R>(this.records, this.timestamp);
+    } finally {
+      this.readLock.unlock();
+    }
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/MembershipStore.java

@@ -0,0 +1,126 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store;
+
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreDriver;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamenodeRegistrationsRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamenodeRegistrationsResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamespaceInfoRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamespaceInfoResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.NamenodeHeartbeatRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.NamenodeHeartbeatResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateNamenodeRegistrationRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateNamenodeRegistrationResponse;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+
+/**
+ * Management API for NameNode registrations stored in
+ * {@link org.apache.hadoop.hdfs.server.federation.store.records.MembershipState
+ * MembershipState} records. The {@link org.apache.hadoop.hdfs.server.
+ * federation.router.RouterHeartbeatService RouterHeartbeatService} periodically
+ * polls each NN to update the NameNode metadata(addresses, operational) and HA
+ * state(active, standby). Each NameNode may be polled by multiple
+ * {@link org.apache.hadoop.hdfs.server.federation.router.Router Router}
+ * instances.
+ * <p>
+ * Once fetched from the
+ * {@link org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreDriver
+ * StateStoreDriver}, NameNode registrations are cached until the next query.
+ * The fetched registration data is aggregated using a quorum to determine the
+ * best/most accurate state for each NameNode. The cache is periodically updated
+ * by the @{link StateStoreCacheUpdateService}.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public abstract class MembershipStore
+    extends CachedRecordStore<MembershipState> {
+
+  protected MembershipStore(StateStoreDriver driver) {
+    super(MembershipState.class, driver, true);
+  }
+
+  /**
+   * Inserts or updates a namenode membership entry into the table.
+   *
+   * @param request Fully populated NamenodeHeartbeatRequest request.
+   * @return True if successful, false otherwise.
+   * @throws StateStoreUnavailableException Throws exception if the data store
+   *           is not initialized.
+   * @throws IOException if the data store could not be queried or the query is
+   *           invalid.
+   */
+  public abstract NamenodeHeartbeatResponse namenodeHeartbeat(
+      NamenodeHeartbeatRequest request) throws IOException;
+
+  /**
+   * Queries for a single cached registration entry matching the given
+   * parameters. Possible keys are the names of data structure elements Possible
+   * values are matching SQL "LIKE" targets.
+   *
+   * @param request Fully populated GetNamenodeRegistrationsRequest request.
+   * @return Single matching FederationMembershipStateEntry or null if not found
+   *         or more than one entry matches.
+   * @throws StateStoreUnavailableException Throws exception if the data store
+   *           is not initialized.
+   * @throws IOException if the data store could not be queried or the query is
+   *           invalid.
+   */
+  public abstract GetNamenodeRegistrationsResponse getNamenodeRegistrations(
+      GetNamenodeRegistrationsRequest request) throws IOException;
+
+  /**
+   * Get the expired registrations from the registration cache.
+   *
+   * @return Expired registrations or zero-length list if none are found.
+   * @throws StateStoreUnavailableException Throws exception if the data store
+   *           is not initialized.
+   * @throws IOException if the data store could not be queried or the query is
+   *           invalid.
+   */
+  public abstract GetNamenodeRegistrationsResponse
+      getExpiredNamenodeRegistrations(GetNamenodeRegistrationsRequest request)
+          throws IOException;
+
+  /**
+   * Retrieves a list of registered nameservices and their associated info.
+   *
+   * @param request
+   * @return Collection of information for each registered nameservice.
+   * @throws IOException if the data store could not be queried or the query is
+   *           invalid.
+   */
+  public abstract GetNamespaceInfoResponse getNamespaceInfo(
+      GetNamespaceInfoRequest request) throws IOException;
+
+  /**
+   * Overrides a cached namenode state with an updated state.
+   *
+   * @param request Fully populated OverrideNamenodeRegistrationRequest request.
+   * @return OverrideNamenodeRegistrationResponse
+   * @throws StateStoreUnavailableException if the data store is not
+   *           initialized.
+   * @throws IOException if the data store could not be queried or the query is
+   *           invalid.
+   */
+  public abstract UpdateNamenodeRegistrationResponse updateNamenodeRegistration(
+      UpdateNamenodeRegistrationRequest request) throws IOException;
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/StateStoreCache.java

@@ -0,0 +1,36 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store;
+
+import java.io.IOException;
+
+/**
+ * Interface for a cached copy of the State Store.
+ */
+public interface StateStoreCache {
+
+  /**
+   * Load the cache from the State Store. Called by the cache update service
+   * when the data has been reloaded.
+   *
+   * @param force If we force the load.
+   * @return If the cache was loaded successfully.
+   * @throws IOException If there was an error loading the cache.
+   */
+  boolean loadCache(boolean force) throws IOException;
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/StateStoreCacheUpdateService.java

@@ -0,0 +1,67 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.server.federation.router.PeriodicService;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Service to periodically update the {@link StateStoreService}
+ * cached information in the
+ * {@link org.apache.hadoop.hdfs.server.federation.router.Router Router}.
+ * This is for performance and removes the State Store from the critical path
+ * in common operations.
+ */
+public class StateStoreCacheUpdateService extends PeriodicService {
+
+  private static final Logger LOG =
+      LoggerFactory.getLogger(StateStoreCacheUpdateService.class);
+
+  /** The service that manages the State Store connection. */
+  private final StateStoreService stateStore;
+
+
+  /**
+   * Create a new Cache update service.
+   *
+   * @param stateStore Implementation of the state store
+   */
+  public StateStoreCacheUpdateService(StateStoreService stateStore) {
+    super(StateStoreCacheUpdateService.class.getSimpleName());
+    this.stateStore = stateStore;
+  }
+
+  @Override
+  protected void serviceInit(Configuration conf) throws Exception {
+
+    this.setIntervalMs(conf.getLong(
+        DFSConfigKeys.DFS_ROUTER_CACHE_TIME_TO_LIVE_MS,
+        DFSConfigKeys.DFS_ROUTER_CACHE_TIME_TO_LIVE_MS_DEFAULT));
+
+    super.serviceInit(conf);
+  }
+
+  @Override
+  public void periodicInvoke() {
+    LOG.debug("Updating State Store cache");
+    stateStore.refreshCaches();
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/StateStoreService.java

@@ -18,17 +18,24 @@
 package org.apache.hadoop.hdfs.server.federation.store;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashMap;
 import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreDriver;
+import org.apache.hadoop.hdfs.server.federation.store.impl.MembershipStoreImpl;
 import org.apache.hadoop.hdfs.server.federation.store.records.BaseRecord;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
 import org.apache.hadoop.service.CompositeService;
 import org.apache.hadoop.util.ReflectionUtils;
+import org.apache.hadoop.util.Time;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -54,6 +61,9 @@
  * federation.
  * <li>{@link MountTableStore}: Mount table between to subclusters.
  * See {@link org.apache.hadoop.fs.viewfs.ViewFs ViewFs}.
+ * <li>{@link RebalancerStore}: Log of the rebalancing operations.
+ * <li>{@link RouterStore}: Router state in the federation.
+ * <li>{@link TokenStore}: Tokens in the federation.
  * </ul>
  */
 @InterfaceAudience.Private
@@ -77,8 +87,30 @@ public class StateStoreService extends CompositeService {
   private StateStoreConnectionMonitorService monitorService;
 
 
+  /** Supported record stores. */
+  private final Map<
+      Class<? extends BaseRecord>, RecordStore<? extends BaseRecord>>
+          recordStores;
+
+  /** Service to maintain State Store caches. */
+  private StateStoreCacheUpdateService cacheUpdater;
+  /** Time the cache was last successfully updated. */
+  private long cacheLastUpdateTime;
+  /** List of internal caches to update. */
+  private final List<StateStoreCache> cachesToUpdateInternal;
+  /** List of external caches to update. */
+  private final List<StateStoreCache> cachesToUpdateExternal;
+
+
   public StateStoreService() {
     super(StateStoreService.class.getName());
+
+    // Records and stores supported by this implementation
+    this.recordStores = new HashMap<>();
+
+    // Caches to maintain
+    this.cachesToUpdateInternal = new ArrayList<>();
+    this.cachesToUpdateExternal = new ArrayList<>();
   }
 
   /**
@@ -102,10 +134,22 @@ protected void serviceInit(Configuration config) throws Exception {
       throw new IOException("Cannot create driver for the State Store");
     }
 
+    // Add supported record stores
+    addRecordStore(MembershipStoreImpl.class);
+
     // Check the connection to the State Store periodically
     this.monitorService = new StateStoreConnectionMonitorService(this);
     this.addService(monitorService);
 
+    // Set expirations intervals for each record
+    MembershipState.setExpirationMs(conf.getLong(
+        DFSConfigKeys.FEDERATION_STORE_MEMBERSHIP_EXPIRATION_MS,
+        DFSConfigKeys.FEDERATION_STORE_MEMBERSHIP_EXPIRATION_MS_DEFAULT));
+
+    // Cache update service
+    this.cacheUpdater = new StateStoreCacheUpdateService(this);
+    addService(this.cacheUpdater);
+
     super.serviceInit(this.conf);
   }
 
@@ -122,14 +166,57 @@ protected void serviceStop() throws Exception {
     super.serviceStop();
   }
 
+  /**
+   * Add a record store to the State Store. It includes adding the store, the
+   * supported record and the cache management.
+   *
+   * @param clazz Class of the record store to track.
+   * @return New record store.
+   * @throws ReflectiveOperationException
+   */
+  private <T extends RecordStore<?>> void addRecordStore(
+      final Class<T> clazz) throws ReflectiveOperationException {
+
+    assert this.getServiceState() == STATE.INITED :
+        "Cannot add record to the State Store once started";
+
+    T recordStore = RecordStore.newInstance(clazz, this.getDriver());
+    Class<? extends BaseRecord> recordClass = recordStore.getRecordClass();
+    this.recordStores.put(recordClass, recordStore);
+
+    // Subscribe for cache updates
+    if (recordStore instanceof StateStoreCache) {
+      StateStoreCache cachedRecordStore = (StateStoreCache) recordStore;
+      this.cachesToUpdateInternal.add(cachedRecordStore);
+    }
+  }
+
+  /**
+   * Get the record store in this State Store for a given interface.
+   *
+   * @param recordStoreClass Class of the record store.
+   * @return Registered record store or null if not found.
+   */
+  public <T extends RecordStore<?>> T getRegisteredRecordStore(
+      final Class<T> recordStoreClass) {
+    for (RecordStore<? extends BaseRecord> recordStore :
+        this.recordStores.values()) {
+      if (recordStoreClass.isInstance(recordStore)) {
+        @SuppressWarnings("unchecked")
+        T recordStoreChecked = (T) recordStore;
+        return recordStoreChecked;
+      }
+    }
+    return null;
+  }
+
   /**
    * List of records supported by this State Store.
    *
    * @return List of supported record classes.
    */
   public Collection<Class<? extends BaseRecord>> getSupportedRecords() {
-    // TODO add list of records
-    return new LinkedList<>();
+    return this.recordStores.keySet();
   }
 
   /**
@@ -142,6 +229,7 @@ public void loadDriver() {
         if (this.driver.init(conf, getIdentifier(), getSupportedRecords())) {
           LOG.info("Connection to the State Store driver {} is open and ready",
               driverName);
+          this.refreshCaches();
         } else {
           LOG.error("Cannot initialize State Store driver {}", driverName);
         }
@@ -198,4 +286,114 @@ public void setIdentifier(String id) {
     this.identifier = id;
   }
 
+  //
+  // Cached state store data
+  //
+  /**
+   * The last time the state store cache was fully updated.
+   *
+   * @return Timestamp.
+   */
+  public long getCacheUpdateTime() {
+    return this.cacheLastUpdateTime;
+  }
+
+  /**
+   * Stops the cache update service.
+   */
+  @VisibleForTesting
+  public void stopCacheUpdateService() {
+    if (this.cacheUpdater != null) {
+      this.cacheUpdater.stop();
+      removeService(this.cacheUpdater);
+      this.cacheUpdater = null;
+    }
+  }
+
+  /**
+   * Register a cached record store for automatic periodic cache updates.
+   *
+   * @param client Client to the state store.
+   */
+  public void registerCacheExternal(StateStoreCache client) {
+    this.cachesToUpdateExternal.add(client);
+  }
+
+  /**
+   * Refresh the cache with information from the State Store. Called
+   * periodically by the CacheUpdateService to maintain data caches and
+   * versions.
+   */
+  public void refreshCaches() {
+    refreshCaches(false);
+  }
+
+  /**
+   * Refresh the cache with information from the State Store. Called
+   * periodically by the CacheUpdateService to maintain data caches and
+   * versions.
+   * @param force If we force the refresh.
+   */
+  public void refreshCaches(boolean force) {
+    boolean success = true;
+    if (isDriverReady()) {
+      List<StateStoreCache> cachesToUpdate = new LinkedList<>();
+      cachesToUpdate.addAll(cachesToUpdateInternal);
+      cachesToUpdate.addAll(cachesToUpdateExternal);
+      for (StateStoreCache cachedStore : cachesToUpdate) {
+        String cacheName = cachedStore.getClass().getSimpleName();
+        boolean result = false;
+        try {
+          result = cachedStore.loadCache(force);
+        } catch (IOException e) {
+          LOG.error("Error updating cache for {}", cacheName, e);
+          result = false;
+        }
+        if (!result) {
+          success = false;
+          LOG.error("Cache update failed for cache {}", cacheName);
+        }
+      }
+    } else {
+      success = false;
+      LOG.info("Skipping State Store cache update, driver is not ready.");
+    }
+    if (success) {
+      // Uses local time, not driver time.
+      this.cacheLastUpdateTime = Time.now();
+    }
+  }
+
+  /**
+   * Update the cache for a specific record store.
+   *
+   * @param clazz Class of the record store.
+   * @return If the cached was loaded.
+   * @throws IOException if the cache update failed.
+   */
+  public boolean loadCache(final Class<?> clazz) throws IOException {
+    return loadCache(clazz, false);
+  }
+
+  /**
+   * Update the cache for a specific record store.
+   *
+   * @param clazz Class of the record store.
+   * @param force Force the update ignoring cached periods.
+   * @return If the cached was loaded.
+   * @throws IOException if the cache update failed.
+   */
+  public boolean loadCache(Class<?> clazz, boolean force) throws IOException {
+    List<StateStoreCache> cachesToUpdate =
+        new LinkedList<StateStoreCache>();
+    cachesToUpdate.addAll(this.cachesToUpdateInternal);
+    cachesToUpdate.addAll(this.cachesToUpdateExternal);
+    for (StateStoreCache cachedStore : cachesToUpdate) {
+      if (clazz.isInstance(cachedStore)) {
+        return cachedStore.loadCache(force);
+      }
+    }
+    throw new IOException("Registered cache was not found for " + clazz);
+  }
+
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/impl/MembershipStoreImpl.java

@@ -0,0 +1,311 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.impl;
+
+import static org.apache.hadoop.hdfs.server.federation.store.StateStoreUtils.filterMultiple;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState;
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamespaceInfo;
+import org.apache.hadoop.hdfs.server.federation.store.MembershipStore;
+import org.apache.hadoop.hdfs.server.federation.store.StateStoreCache;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreDriver;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamenodeRegistrationsRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamenodeRegistrationsResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamespaceInfoRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamespaceInfoResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.NamenodeHeartbeatRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.NamenodeHeartbeatResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateNamenodeRegistrationRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateNamenodeRegistrationResponse;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+import org.apache.hadoop.hdfs.server.federation.store.records.Query;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Implementation of the {@link MembershipStore} State Store API.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+public class MembershipStoreImpl
+    extends MembershipStore implements StateStoreCache {
+
+  private static final Logger LOG =
+      LoggerFactory.getLogger(MembershipStoreImpl.class);
+
+
+  /** Reported namespaces that are not decommissioned. */
+  private final Set<FederationNamespaceInfo> activeNamespaces;
+
+  /** Namenodes (after evaluating the quorum) that are active in the cluster. */
+  private final Map<String, MembershipState> activeRegistrations;
+  /** Namenode status reports (raw) that were discarded for being too old. */
+  private final Map<String, MembershipState> expiredRegistrations;
+
+  /** Lock to access the local memory cache. */
+  private final ReadWriteLock cacheReadWriteLock =
+      new ReentrantReadWriteLock();
+  private final Lock cacheReadLock = cacheReadWriteLock.readLock();
+  private final Lock cacheWriteLock = cacheReadWriteLock.writeLock();
+
+
+  public MembershipStoreImpl(StateStoreDriver driver) {
+    super(driver);
+
+    this.activeRegistrations = new HashMap<>();
+    this.expiredRegistrations = new HashMap<>();
+    this.activeNamespaces = new TreeSet<>();
+  }
+
+  @Override
+  public GetNamenodeRegistrationsResponse getExpiredNamenodeRegistrations(
+      GetNamenodeRegistrationsRequest request) throws IOException {
+
+    GetNamenodeRegistrationsResponse response =
+        GetNamenodeRegistrationsResponse.newInstance();
+    cacheReadLock.lock();
+    try {
+      Collection<MembershipState> vals = this.expiredRegistrations.values();
+      List<MembershipState> copyVals = new ArrayList<>(vals);
+      response.setNamenodeMemberships(copyVals);
+    } finally {
+      cacheReadLock.unlock();
+    }
+    return response;
+  }
+
+  @Override
+  public GetNamespaceInfoResponse getNamespaceInfo(
+      GetNamespaceInfoRequest request) throws IOException {
+
+    Set<FederationNamespaceInfo> namespaces = new HashSet<>();
+    try {
+      cacheReadLock.lock();
+      namespaces.addAll(activeNamespaces);
+    } finally {
+      cacheReadLock.unlock();
+    }
+
+    GetNamespaceInfoResponse response =
+        GetNamespaceInfoResponse.newInstance(namespaces);
+    return response;
+  }
+
+  @Override
+  public GetNamenodeRegistrationsResponse getNamenodeRegistrations(
+      final GetNamenodeRegistrationsRequest request) throws IOException {
+
+    // TODO Cache some common queries and sorts
+    List<MembershipState> ret = null;
+
+    cacheReadLock.lock();
+    try {
+      Collection<MembershipState> registrations = activeRegistrations.values();
+      MembershipState partialMembership = request.getPartialMembership();
+      if (partialMembership == null) {
+        ret = new ArrayList<>(registrations);
+      } else {
+        Query<MembershipState> query = new Query<>(partialMembership);
+        ret = filterMultiple(query, registrations);
+      }
+    } finally {
+      cacheReadLock.unlock();
+    }
+    // Sort in ascending update date order
+    Collections.sort(ret);
+
+    GetNamenodeRegistrationsResponse response =
+        GetNamenodeRegistrationsResponse.newInstance(ret);
+    return response;
+  }
+
+  @Override
+  public NamenodeHeartbeatResponse namenodeHeartbeat(
+      NamenodeHeartbeatRequest request) throws IOException {
+
+    MembershipState record = request.getNamenodeMembership();
+    String nnId = record.getNamenodeKey();
+    MembershipState existingEntry = null;
+    cacheReadLock.lock();
+    try {
+      existingEntry = this.activeRegistrations.get(nnId);
+    } finally {
+      cacheReadLock.unlock();
+    }
+
+    if (existingEntry != null) {
+      if (existingEntry.getState() != record.getState()) {
+        LOG.info("NN registration state has changed: {} -> {}",
+            existingEntry, record);
+      } else {
+        LOG.debug("Updating NN registration: {} -> {}", existingEntry, record);
+      }
+    } else {
+      LOG.info("Inserting new NN registration: {}", record);
+    }
+
+    boolean status = getDriver().put(record, true, false);
+
+    NamenodeHeartbeatResponse response =
+        NamenodeHeartbeatResponse.newInstance(status);
+    return response;
+  }
+
+  @Override
+  public boolean loadCache(boolean force) throws IOException {
+    super.loadCache(force);
+
+    // Update local cache atomically
+    cacheWriteLock.lock();
+    try {
+      this.activeRegistrations.clear();
+      this.expiredRegistrations.clear();
+      this.activeNamespaces.clear();
+
+      // Build list of NN registrations: nnId -> registration list
+      Map<String, List<MembershipState>> nnRegistrations = new HashMap<>();
+      List<MembershipState> cachedRecords = getCachedRecords();
+      for (MembershipState membership : cachedRecords) {
+        String nnId = membership.getNamenodeKey();
+        if (membership.getState() == FederationNamenodeServiceState.EXPIRED) {
+          // Expired, RPC service does not use these
+          String key = membership.getPrimaryKey();
+          this.expiredRegistrations.put(key, membership);
+        } else {
+          // This is a valid NN registration, build a list of all registrations
+          // using the NN id to use for the quorum calculation.
+          List<MembershipState> nnRegistration =
+              nnRegistrations.get(nnId);
+          if (nnRegistration == null) {
+            nnRegistration = new LinkedList<>();
+            nnRegistrations.put(nnId, nnRegistration);
+          }
+          nnRegistration.add(membership);
+          String bpId = membership.getBlockPoolId();
+          String cId = membership.getClusterId();
+          String nsId = membership.getNameserviceId();
+          FederationNamespaceInfo nsInfo =
+              new FederationNamespaceInfo(bpId, cId, nsId);
+          this.activeNamespaces.add(nsInfo);
+        }
+      }
+
+      // Calculate most representative entry for each active NN id
+      for (List<MembershipState> nnRegistration : nnRegistrations.values()) {
+        // Run quorum based on NN state
+        MembershipState representativeRecord =
+            getRepresentativeQuorum(nnRegistration);
+        String nnKey = representativeRecord.getNamenodeKey();
+        this.activeRegistrations.put(nnKey, representativeRecord);
+      }
+      LOG.debug("Refreshed {} NN registrations from State Store",
+          cachedRecords.size());
+    } finally {
+      cacheWriteLock.unlock();
+    }
+    return true;
+  }
+
+  @Override
+  public UpdateNamenodeRegistrationResponse updateNamenodeRegistration(
+      UpdateNamenodeRegistrationRequest request) throws IOException {
+
+    boolean status = false;
+    cacheWriteLock.lock();
+    try {
+      String namenode = MembershipState.getNamenodeKey(
+          request.getNameserviceId(), request.getNamenodeId());
+      MembershipState member = this.activeRegistrations.get(namenode);
+      if (member != null) {
+        member.setState(request.getState());
+        status = true;
+      }
+    } finally {
+      cacheWriteLock.unlock();
+    }
+    UpdateNamenodeRegistrationResponse response =
+        UpdateNamenodeRegistrationResponse.newInstance(status);
+    return response;
+  }
+
+  /**
+   * Picks the most recent entry in the subset that is most agreeable on the
+   * specified field. 1) If a majority of the collection has the same value for
+   * the field, the first sorted entry within the subset the matches the
+   * majority value 2) Otherwise the first sorted entry in the set of all
+   * entries
+   *
+   * @param entries - Collection of state store record objects of the same type
+   * @param fieldName - Field name for the value to compare
+   * @return record that is most representative of the field name
+   */
+  private MembershipState getRepresentativeQuorum(
+      Collection<MembershipState> records) {
+
+    // Collate objects by field value: field value -> order set of records
+    Map<FederationNamenodeServiceState, TreeSet<MembershipState>> occurenceMap =
+        new HashMap<>();
+    for (MembershipState record : records) {
+      FederationNamenodeServiceState state = record.getState();
+      TreeSet<MembershipState> matchingSet = occurenceMap.get(state);
+      if (matchingSet == null) {
+        // TreeSet orders elements by descending date via comparators
+        matchingSet = new TreeSet<>();
+        occurenceMap.put(state, matchingSet);
+      }
+      matchingSet.add(record);
+    }
+
+    // Select largest group
+    TreeSet<MembershipState> largestSet = new TreeSet<>();
+    for (TreeSet<MembershipState> matchingSet : occurenceMap.values()) {
+      if (largestSet.size() < matchingSet.size()) {
+        largestSet = matchingSet;
+      }
+    }
+
+    // If quorum, use the newest element here
+    if (largestSet.size() > records.size() / 2) {
+      return largestSet.first();
+      // Otherwise, return most recent by class comparator
+    } else if (records.size() > 0) {
+      TreeSet<MembershipState> sortedList = new TreeSet<>(records);
+      LOG.debug("Quorum failed, using most recent: {}", sortedList.first());
+      return sortedList.first();
+    } else {
+      return null;
+    }
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/impl/package-info.java

@@ -0,0 +1,31 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Contains implementations of the state store API interfaces. All classes
+ * derive from {@link
+ * org.apache.hadoop.hdfs.server.federation.store.RecordStore}. The API
+ * definitions are contained in the
+ * org.apache.hadoop.hdfs.server.federation.store package.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+package org.apache.hadoop.hdfs.server.federation.store.impl;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/GetNamenodeRegistrationsRequest.java

@@ -0,0 +1,52 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol;
+
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience.Public;
+import org.apache.hadoop.classification.InterfaceStability.Unstable;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+
+/**
+ * API request for listing namenode registrations present in the state store.
+ */
+public abstract class GetNamenodeRegistrationsRequest {
+
+  public static GetNamenodeRegistrationsRequest newInstance()
+      throws IOException {
+    return StateStoreSerializer.newRecord(
+        GetNamenodeRegistrationsRequest.class);
+  }
+
+  public static GetNamenodeRegistrationsRequest newInstance(
+      MembershipState member) throws IOException {
+    GetNamenodeRegistrationsRequest request = newInstance();
+    request.setPartialMembership(member);
+    return request;
+  }
+
+  @Public
+  @Unstable
+  public abstract MembershipState getPartialMembership();
+
+  @Public
+  @Unstable
+  public abstract void setPartialMembership(MembershipState member);
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/GetNamenodeRegistrationsResponse.java

@@ -0,0 +1,55 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol;
+
+import java.io.IOException;
+import java.util.List;
+
+import org.apache.hadoop.classification.InterfaceAudience.Public;
+import org.apache.hadoop.classification.InterfaceStability.Unstable;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+
+/**
+ * API response for listing namenode registrations present in the state store.
+ */
+public abstract class GetNamenodeRegistrationsResponse {
+
+  public static GetNamenodeRegistrationsResponse newInstance()
+      throws IOException {
+    return StateStoreSerializer.newRecord(
+        GetNamenodeRegistrationsResponse.class);
+  }
+
+  public static GetNamenodeRegistrationsResponse newInstance(
+      List<MembershipState> records) throws IOException {
+    GetNamenodeRegistrationsResponse response = newInstance();
+    response.setNamenodeMemberships(records);
+    return response;
+  }
+
+  @Public
+  @Unstable
+  public abstract List<MembershipState> getNamenodeMemberships()
+      throws IOException;
+
+  @Public
+  @Unstable
+  public abstract void setNamenodeMemberships(
+      List<MembershipState> records) throws IOException;
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/GetNamespaceInfoRequest.java

@@ -0,0 +1,30 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol;
+
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+
+/**
+ * API response for listing HDFS namespaces present in the state store.
+ */
+public abstract class GetNamespaceInfoRequest {
+
+  public static GetNamespaceInfoRequest newInstance() {
+    return StateStoreSerializer.newRecord(GetNamespaceInfoRequest.class);
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/GetNamespaceInfoResponse.java

@@ -0,0 +1,52 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol;
+
+import java.io.IOException;
+import java.util.Set;
+
+import org.apache.hadoop.classification.InterfaceAudience.Public;
+import org.apache.hadoop.classification.InterfaceStability.Unstable;
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamespaceInfo;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+
+/**
+ * API response for listing HDFS namespaces present in the state store.
+ */
+public abstract class GetNamespaceInfoResponse {
+
+  public static GetNamespaceInfoResponse newInstance() {
+    return StateStoreSerializer.newRecord(GetNamespaceInfoResponse.class);
+  }
+
+  public static GetNamespaceInfoResponse newInstance(
+      Set<FederationNamespaceInfo> namespaces) throws IOException {
+    GetNamespaceInfoResponse response = newInstance();
+    response.setNamespaceInfo(namespaces);
+    return response;
+  }
+
+  @Public
+  @Unstable
+  public abstract Set<FederationNamespaceInfo> getNamespaceInfo();
+
+  @Public
+  @Unstable
+  public abstract void setNamespaceInfo(
+      Set<FederationNamespaceInfo> namespaceInfo);
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/NamenodeHeartbeatRequest.java

@@ -0,0 +1,52 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol;
+
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience.Private;
+import org.apache.hadoop.classification.InterfaceStability.Unstable;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+
+/**
+ * API request for registering a namenode with the state store.
+ */
+public abstract class NamenodeHeartbeatRequest {
+
+  public static NamenodeHeartbeatRequest newInstance() throws IOException {
+    return StateStoreSerializer.newRecord(NamenodeHeartbeatRequest.class);
+  }
+
+  public static NamenodeHeartbeatRequest newInstance(MembershipState namenode)
+      throws IOException {
+    NamenodeHeartbeatRequest request = newInstance();
+    request.setNamenodeMembership(namenode);
+    return request;
+  }
+
+  @Private
+  @Unstable
+  public abstract MembershipState getNamenodeMembership()
+      throws IOException;
+
+  @Private
+  @Unstable
+  public abstract void setNamenodeMembership(MembershipState report)
+      throws IOException;
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/NamenodeHeartbeatResponse.java

@@ -0,0 +1,49 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol;
+
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience.Private;
+import org.apache.hadoop.classification.InterfaceStability.Unstable;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+
+/**
+ * API response for registering a namenode with the state store.
+ */
+public abstract class NamenodeHeartbeatResponse {
+
+  public static NamenodeHeartbeatResponse newInstance() throws IOException {
+    return StateStoreSerializer.newRecord(NamenodeHeartbeatResponse.class);
+  }
+
+  public static NamenodeHeartbeatResponse newInstance(boolean status)
+      throws IOException {
+    NamenodeHeartbeatResponse response = newInstance();
+    response.setResult(status);
+    return response;
+  }
+
+  @Private
+  @Unstable
+  public abstract boolean getResult();
+
+  @Private
+  @Unstable
+  public abstract void setResult(boolean result);
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/UpdateNamenodeRegistrationRequest.java

@@ -0,0 +1,72 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol;
+
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience.Private;
+import org.apache.hadoop.classification.InterfaceStability.Unstable;
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+
+/**
+ * API request for overriding an existing namenode registration in the state
+ * store.
+ */
+public abstract class UpdateNamenodeRegistrationRequest {
+
+  public static UpdateNamenodeRegistrationRequest newInstance()
+      throws IOException {
+    return StateStoreSerializer.newRecord(
+        UpdateNamenodeRegistrationRequest.class);
+  }
+
+  public static UpdateNamenodeRegistrationRequest newInstance(
+      String nameserviceId, String namenodeId,
+      FederationNamenodeServiceState state) throws IOException {
+    UpdateNamenodeRegistrationRequest request = newInstance();
+    request.setNameserviceId(nameserviceId);
+    request.setNamenodeId(namenodeId);
+    request.setState(state);
+    return request;
+  }
+
+  @Private
+  @Unstable
+  public abstract String getNameserviceId();
+
+  @Private
+  @Unstable
+  public abstract String getNamenodeId();
+
+  @Private
+  @Unstable
+  public abstract FederationNamenodeServiceState getState();
+
+  @Private
+  @Unstable
+  public abstract void setNameserviceId(String nsId);
+
+  @Private
+  @Unstable
+  public abstract void setNamenodeId(String nnId);
+
+  @Private
+  @Unstable
+  public abstract void setState(FederationNamenodeServiceState state);
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/UpdateNamenodeRegistrationResponse.java

@@ -0,0 +1,51 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol;
+
+import java.io.IOException;
+
+import org.apache.hadoop.classification.InterfaceAudience.Private;
+import org.apache.hadoop.classification.InterfaceStability.Unstable;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+
+/**
+ * API response for overriding an existing namenode registration in the state
+ * store.
+ */
+public abstract class UpdateNamenodeRegistrationResponse {
+
+  public static UpdateNamenodeRegistrationResponse newInstance() {
+    return StateStoreSerializer.newRecord(
+        UpdateNamenodeRegistrationResponse.class);
+  }
+
+  public static UpdateNamenodeRegistrationResponse newInstance(boolean status)
+      throws IOException {
+    UpdateNamenodeRegistrationResponse response = newInstance();
+    response.setResult(status);
+    return response;
+  }
+
+  @Private
+  @Unstable
+  public abstract boolean getResult();
+
+  @Private
+  @Unstable
+  public abstract void setResult(boolean result);
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/impl/pb/FederationProtocolPBTranslator.java

@@ -0,0 +1,145 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb;
+
+import java.io.IOException;
+import java.lang.reflect.Method;
+
+import org.apache.commons.codec.binary.Base64;
+
+import com.google.protobuf.GeneratedMessage;
+import com.google.protobuf.Message;
+import com.google.protobuf.Message.Builder;
+import com.google.protobuf.MessageOrBuilder;
+
+/**
+ * Helper class for setting/getting data elements in an object backed by a
+ * protobuf implementation.
+ */
+public class FederationProtocolPBTranslator<P extends GeneratedMessage,
+    B extends Builder, T extends MessageOrBuilder> {
+
+  /** Optional proto byte stream used to create this object. */
+  private P proto;
+  /** The class of the proto handler for this translator. */
+  private Class<P> protoClass;
+  /** Internal builder, used to store data that has been set. */
+  private B builder;
+
+  public FederationProtocolPBTranslator(Class<P> protoType) {
+    this.protoClass = protoType;
+  }
+
+  /**
+   * Called if this translator is to be created from an existing protobuf byte
+   * stream.
+   *
+   * @param p The existing proto object to use to initialize the translator.
+   * @throws IllegalArgumentException
+   */
+  @SuppressWarnings("unchecked")
+  public void setProto(Message p) {
+    if (protoClass.isInstance(p)) {
+      if (this.builder != null) {
+        // Merge with builder
+        this.builder.mergeFrom((P) p);
+      } else {
+        // Store proto
+        this.proto = (P) p;
+      }
+    } else {
+      throw new IllegalArgumentException(
+          "Cannot decode proto type " + p.getClass().getName());
+    }
+  }
+
+  /**
+   * Create or return the cached protobuf builder for this translator.
+   *
+   * @return cached Builder instance
+   */
+  @SuppressWarnings("unchecked")
+  public B getBuilder() {
+    if (this.builder == null) {
+      try {
+        Method method = protoClass.getMethod("newBuilder");
+        this.builder = (B) method.invoke(null);
+        if (this.proto != null) {
+          // Merge in existing immutable proto
+          this.builder.mergeFrom(this.proto);
+        }
+      } catch (ReflectiveOperationException e) {
+        this.builder = null;
+      }
+    }
+    return this.builder;
+  }
+
+  /**
+   * Get the serialized proto object. If the translator was created from a byte
+   * stream, returns the intitial byte stream. Otherwise creates a new byte
+   * stream from the cached builder.
+   *
+   * @return Protobuf message object
+   */
+  @SuppressWarnings("unchecked")
+  public P build() {
+    if (this.builder != null) {
+      // serialize from builder (mutable) first
+      Message m = this.builder.build();
+      return (P) m;
+    } else if (this.proto != null) {
+      // Use immutable message source, message is unchanged
+      return this.proto;
+    }
+    return null;
+  }
+
+  /**
+   * Returns an interface to access data stored within this object. The object
+   * may have been initialized either via a builder or by an existing protobuf
+   * byte stream.
+   *
+   * @return MessageOrBuilder protobuf interface for the requested class.
+   */
+  @SuppressWarnings("unchecked")
+  public T getProtoOrBuilder() {
+    if (this.builder != null) {
+      // Use mutable builder if it exists
+      return (T) this.builder;
+    } else if (this.proto != null) {
+      // Use immutable message source
+      return (T) this.proto;
+    } else {
+      // Construct empty builder
+      return (T) this.getBuilder();
+    }
+  }
+
+  /**
+   * Read instance from base64 data.
+   * @param base64String
+   * @throws IOException
+   */
+  @SuppressWarnings("unchecked")
+  public void readInstance(String base64String) throws IOException {
+    byte[] bytes = Base64.decodeBase64(base64String);
+    Message msg = getBuilder().mergeFrom(bytes).build();
+    this.proto = (P) msg;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/impl/pb/GetNamenodeRegistrationsRequestPBImpl.java

@@ -0,0 +1,87 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.GetNamenodeRegistrationsRequestProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.GetNamenodeRegistrationsRequestProtoOrBuilder;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeMembershipRecordProto;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamenodeRegistrationsRequest;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.MembershipStatePBImpl;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.PBRecord;
+
+import com.google.protobuf.Message;
+
+/**
+ * Protobuf implementation of the state store API object
+ * GetNamenodeRegistrationsRequest.
+ */
+public class GetNamenodeRegistrationsRequestPBImpl
+    extends GetNamenodeRegistrationsRequest implements PBRecord {
+
+  private FederationProtocolPBTranslator<GetNamenodeRegistrationsRequestProto,
+      GetNamenodeRegistrationsRequestProto.Builder,
+      GetNamenodeRegistrationsRequestProtoOrBuilder> translator =
+          new FederationProtocolPBTranslator<
+              GetNamenodeRegistrationsRequestProto,
+              GetNamenodeRegistrationsRequestProto.Builder,
+              GetNamenodeRegistrationsRequestProtoOrBuilder>(
+                  GetNamenodeRegistrationsRequestProto.class);
+
+  public GetNamenodeRegistrationsRequestPBImpl() {
+  }
+
+  public GetNamenodeRegistrationsRequestPBImpl(
+      GetNamenodeRegistrationsRequestProto proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public GetNamenodeRegistrationsRequestProto getProto() {
+    return this.translator.build();
+  }
+
+  @Override
+  public void setProto(Message proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public void readInstance(String base64String) throws IOException {
+    this.translator.readInstance(base64String);
+  }
+
+  @Override
+  public MembershipState getPartialMembership() {
+    GetNamenodeRegistrationsRequestProtoOrBuilder proto =
+        this.translator.getProtoOrBuilder();
+    if (!proto.hasMembership()){
+      return null;
+    }
+    NamenodeMembershipRecordProto memberProto = proto.getMembership();
+    return new MembershipStatePBImpl(memberProto);
+  }
+
+  @Override
+  public void setPartialMembership(MembershipState member) {
+    MembershipStatePBImpl memberPB = (MembershipStatePBImpl)member;
+    this.translator.getBuilder().setMembership(memberPB.getProto());
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/impl/pb/GetNamenodeRegistrationsResponsePBImpl.java

@@ -0,0 +1,99 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.GetNamenodeRegistrationsResponseProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.GetNamenodeRegistrationsResponseProtoOrBuilder;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeMembershipRecordProto;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamenodeRegistrationsResponse;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.MembershipStatePBImpl;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.PBRecord;
+
+import com.google.protobuf.Message;
+
+/**
+ * Protobuf implementation of the state store API object
+ * GetNamenodeRegistrationsResponse.
+ */
+public class GetNamenodeRegistrationsResponsePBImpl
+    extends GetNamenodeRegistrationsResponse implements PBRecord {
+
+  private FederationProtocolPBTranslator<GetNamenodeRegistrationsResponseProto,
+      GetNamenodeRegistrationsResponseProto.Builder,
+      GetNamenodeRegistrationsResponseProtoOrBuilder> translator =
+          new FederationProtocolPBTranslator<
+              GetNamenodeRegistrationsResponseProto,
+              GetNamenodeRegistrationsResponseProto.Builder,
+              GetNamenodeRegistrationsResponseProtoOrBuilder>(
+                  GetNamenodeRegistrationsResponseProto.class);
+
+  public GetNamenodeRegistrationsResponsePBImpl() {
+  }
+
+  public GetNamenodeRegistrationsResponsePBImpl(
+      GetNamenodeRegistrationsResponseProto proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public GetNamenodeRegistrationsResponseProto getProto() {
+    return this.translator.build();
+  }
+
+  @Override
+  public void setProto(Message proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public void readInstance(String base64String) throws IOException {
+    this.translator.readInstance(base64String);
+  }
+
+  @Override
+  public List<MembershipState> getNamenodeMemberships()
+      throws IOException {
+
+    List<MembershipState> ret = new ArrayList<MembershipState>();
+    List<NamenodeMembershipRecordProto> memberships =
+        this.translator.getProtoOrBuilder().getNamenodeMembershipsList();
+    for (NamenodeMembershipRecordProto memberProto : memberships) {
+      MembershipState membership = new MembershipStatePBImpl(memberProto);
+      ret.add(membership);
+    }
+
+    return ret;
+  }
+
+  @Override
+  public void setNamenodeMemberships(List<MembershipState> records)
+      throws IOException {
+    for (MembershipState member : records) {
+      if (member instanceof MembershipStatePBImpl) {
+        MembershipStatePBImpl memberPB = (MembershipStatePBImpl)member;
+        this.translator.getBuilder().addNamenodeMemberships(
+            memberPB.getProto());
+      }
+    }
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/impl/pb/GetNamespaceInfoRequestPBImpl.java

@@ -0,0 +1,60 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.GetNamespaceInfoRequestProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.GetNamespaceInfoRequestProto.Builder;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.GetNamespaceInfoRequestProtoOrBuilder;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamespaceInfoRequest;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.PBRecord;
+
+import com.google.protobuf.Message;
+
+/**
+ * Protobuf implementation of the state store API object
+ * GetNamespaceInfoRequest.
+ */
+public class GetNamespaceInfoRequestPBImpl extends GetNamespaceInfoRequest
+    implements PBRecord {
+
+  private FederationProtocolPBTranslator<GetNamespaceInfoRequestProto,
+      Builder, GetNamespaceInfoRequestProtoOrBuilder> translator =
+          new FederationProtocolPBTranslator<GetNamespaceInfoRequestProto,
+              Builder, GetNamespaceInfoRequestProtoOrBuilder>(
+                  GetNamespaceInfoRequestProto.class);
+
+  public GetNamespaceInfoRequestPBImpl() {
+  }
+
+  @Override
+  public GetNamespaceInfoRequestProto getProto() {
+    return this.translator.build();
+  }
+
+  @Override
+  public void setProto(Message protocol) {
+    this.translator.setProto(protocol);
+  }
+
+  @Override
+  public void readInstance(String base64String) throws IOException {
+    this.translator.readInstance(base64String);
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/impl/pb/GetNamespaceInfoResponsePBImpl.java

@@ -0,0 +1,95 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb;
+
+import java.io.IOException;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.FederationNamespaceInfoProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.GetNamespaceInfoResponseProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.GetNamespaceInfoResponseProtoOrBuilder;
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamespaceInfo;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamespaceInfoResponse;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.PBRecord;
+
+import com.google.protobuf.Message;
+
+/**
+ * Protobuf implementation of the state store API object
+ * GetNamespaceInfoResponse.
+ */
+public class GetNamespaceInfoResponsePBImpl
+    extends GetNamespaceInfoResponse implements PBRecord {
+
+  private FederationProtocolPBTranslator<GetNamespaceInfoResponseProto,
+      GetNamespaceInfoResponseProto.Builder,
+      GetNamespaceInfoResponseProtoOrBuilder> translator =
+          new FederationProtocolPBTranslator<GetNamespaceInfoResponseProto,
+              GetNamespaceInfoResponseProto.Builder,
+              GetNamespaceInfoResponseProtoOrBuilder>(
+                  GetNamespaceInfoResponseProto.class);
+
+  public GetNamespaceInfoResponsePBImpl() {
+  }
+
+  @Override
+  public GetNamespaceInfoResponseProto getProto() {
+    return this.translator.build();
+  }
+
+  @Override
+  public void setProto(Message protocol) {
+    this.translator.setProto(protocol);
+  }
+
+  @Override
+  public void readInstance(String base64String) throws IOException {
+    this.translator.readInstance(base64String);
+  }
+
+  @Override
+  public Set<FederationNamespaceInfo> getNamespaceInfo() {
+
+    Set<FederationNamespaceInfo> ret = new HashSet<FederationNamespaceInfo>();
+    List<FederationNamespaceInfoProto> namespaceList =
+        this.translator.getProtoOrBuilder().getNamespaceInfosList();
+    for (FederationNamespaceInfoProto ns : namespaceList) {
+      FederationNamespaceInfo info = new FederationNamespaceInfo(
+          ns.getBlockPoolId(), ns.getClusterId(), ns.getNameserviceId());
+      ret.add(info);
+    }
+    return ret;
+  }
+
+  @Override
+  public void setNamespaceInfo(Set<FederationNamespaceInfo> namespaceInfo) {
+    int index = 0;
+    for (FederationNamespaceInfo item : namespaceInfo) {
+      FederationNamespaceInfoProto.Builder itemBuilder =
+          FederationNamespaceInfoProto.newBuilder();
+      itemBuilder.setClusterId(item.getClusterId());
+      itemBuilder.setBlockPoolId(item.getBlockPoolId());
+      itemBuilder.setNameserviceId(item.getNameserviceId());
+      this.translator.getBuilder().addNamespaceInfos(index,
+          itemBuilder.build());
+      index++;
+    }
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/impl/pb/NamenodeHeartbeatRequestPBImpl.java

@@ -0,0 +1,93 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeHeartbeatRequestProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeHeartbeatRequestProto.Builder;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeHeartbeatRequestProtoOrBuilder;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeMembershipRecordProto;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.NamenodeHeartbeatRequest;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.MembershipStatePBImpl;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.PBRecord;
+
+import com.google.protobuf.Message;
+
+/**
+ * Protobuf implementation of the state store API object
+ * NamenodeHeartbeatRequest.
+ */
+public class NamenodeHeartbeatRequestPBImpl
+    extends NamenodeHeartbeatRequest implements PBRecord {
+
+  private FederationProtocolPBTranslator<NamenodeHeartbeatRequestProto, Builder,
+      NamenodeHeartbeatRequestProtoOrBuilder> translator =
+          new FederationProtocolPBTranslator<NamenodeHeartbeatRequestProto,
+              Builder,
+              NamenodeHeartbeatRequestProtoOrBuilder>(
+                  NamenodeHeartbeatRequestProto.class);
+
+  public NamenodeHeartbeatRequestPBImpl() {
+  }
+
+  @Override
+  public NamenodeHeartbeatRequestProto getProto() {
+    return this.translator.build();
+  }
+
+  @Override
+  public void setProto(Message proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public void readInstance(String base64String) throws IOException {
+    this.translator.readInstance(base64String);
+  }
+
+  @Override
+  public MembershipState getNamenodeMembership() throws IOException {
+    NamenodeMembershipRecordProto membershipProto =
+        this.translator.getProtoOrBuilder().getNamenodeMembership();
+    MembershipState membership =
+        StateStoreSerializer.newRecord(MembershipState.class);
+    if (membership instanceof MembershipStatePBImpl) {
+      MembershipStatePBImpl membershipPB = (MembershipStatePBImpl)membership;
+      membershipPB.setProto(membershipProto);
+      return membershipPB;
+    } else {
+      throw new IOException("Cannot get membership from request");
+    }
+  }
+
+  @Override
+  public void setNamenodeMembership(MembershipState membership)
+      throws IOException {
+    if (membership instanceof MembershipStatePBImpl) {
+      MembershipStatePBImpl membershipPB = (MembershipStatePBImpl)membership;
+      NamenodeMembershipRecordProto membershipProto =
+          (NamenodeMembershipRecordProto)membershipPB.getProto();
+      this.translator.getBuilder().setNamenodeMembership(membershipProto);
+    } else {
+      throw new IOException("Cannot set mount table entry");
+    }
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/impl/pb/NamenodeHeartbeatResponsePBImpl.java

@@ -0,0 +1,71 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeHeartbeatResponseProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeHeartbeatResponseProtoOrBuilder;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.NamenodeHeartbeatResponse;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.PBRecord;
+
+import com.google.protobuf.Message;
+
+/**
+ * Protobuf implementation of the state store API object
+ * NamenodeHeartbeatResponse.
+ */
+public class NamenodeHeartbeatResponsePBImpl extends NamenodeHeartbeatResponse
+    implements PBRecord {
+
+  private FederationProtocolPBTranslator<NamenodeHeartbeatResponseProto,
+      NamenodeHeartbeatResponseProto.Builder,
+      NamenodeHeartbeatResponseProtoOrBuilder> translator =
+          new FederationProtocolPBTranslator<NamenodeHeartbeatResponseProto,
+              NamenodeHeartbeatResponseProto.Builder,
+              NamenodeHeartbeatResponseProtoOrBuilder>(
+                  NamenodeHeartbeatResponseProto.class);
+
+  public NamenodeHeartbeatResponsePBImpl() {
+  }
+
+  @Override
+  public NamenodeHeartbeatResponseProto getProto() {
+    return this.translator.build();
+  }
+
+  @Override
+  public void setProto(Message proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public void readInstance(String base64String) throws IOException {
+    this.translator.readInstance(base64String);
+  }
+
+  @Override
+  public boolean getResult() {
+    return this.translator.getProtoOrBuilder().getStatus();
+  }
+
+  @Override
+  public void setResult(boolean result) {
+    this.translator.getBuilder().setStatus(result);
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/impl/pb/UpdateNamenodeRegistrationRequestPBImpl.java

@@ -0,0 +1,95 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.UpdateNamenodeRegistrationRequestProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.UpdateNamenodeRegistrationRequestProtoOrBuilder;
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateNamenodeRegistrationRequest;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.PBRecord;
+
+import com.google.protobuf.Message;
+
+/**
+ * Protobuf implementation of the state store API object
+ * OverrideNamenodeRegistrationRequest.
+ */
+public class UpdateNamenodeRegistrationRequestPBImpl
+    extends UpdateNamenodeRegistrationRequest implements PBRecord {
+
+  private FederationProtocolPBTranslator<
+      UpdateNamenodeRegistrationRequestProto,
+      UpdateNamenodeRegistrationRequestProto.Builder,
+      UpdateNamenodeRegistrationRequestProtoOrBuilder> translator =
+          new FederationProtocolPBTranslator<
+              UpdateNamenodeRegistrationRequestProto,
+              UpdateNamenodeRegistrationRequestProto.Builder,
+              UpdateNamenodeRegistrationRequestProtoOrBuilder>(
+                  UpdateNamenodeRegistrationRequestProto.class);
+
+  public UpdateNamenodeRegistrationRequestPBImpl() {
+  }
+
+  @Override
+  public UpdateNamenodeRegistrationRequestProto getProto() {
+    return this.translator.build();
+  }
+
+  @Override
+  public void setProto(Message protocol) {
+    this.translator.setProto(protocol);
+  }
+
+  @Override
+  public void readInstance(String base64String) throws IOException {
+    this.translator.readInstance(base64String);
+  }
+
+  @Override
+  public String getNameserviceId() {
+    return this.translator.getProtoOrBuilder().getNameserviceId();
+  }
+
+  @Override
+  public String getNamenodeId() {
+    return this.translator.getProtoOrBuilder().getNamenodeId();
+  }
+
+  @Override
+  public FederationNamenodeServiceState getState() {
+    return FederationNamenodeServiceState
+        .valueOf(this.translator.getProtoOrBuilder().getState());
+  }
+
+  @Override
+  public void setNameserviceId(String nsId) {
+    this.translator.getBuilder().setNameserviceId(nsId);
+  }
+
+  @Override
+  public void setNamenodeId(String nnId) {
+    this.translator.getBuilder().setNamenodeId(nnId);
+  }
+
+  @Override
+  public void setState(FederationNamenodeServiceState state) {
+    this.translator.getBuilder().setState(state.toString());
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/impl/pb/UpdateNamenodeRegistrationResponsePBImpl.java

@@ -0,0 +1,73 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.UpdateNamenodeRegistrationResponseProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.UpdateNamenodeRegistrationResponseProtoOrBuilder;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateNamenodeRegistrationResponse;
+import org.apache.hadoop.hdfs.server.federation.store.records.impl.pb.PBRecord;
+
+import com.google.protobuf.Message;
+
+/**
+ * Protobuf implementation of the state store API object
+ * OverrideNamenodeRegistrationResponse.
+ */
+public class UpdateNamenodeRegistrationResponsePBImpl
+    extends UpdateNamenodeRegistrationResponse implements PBRecord {
+
+  private FederationProtocolPBTranslator<
+      UpdateNamenodeRegistrationResponseProto,
+      UpdateNamenodeRegistrationResponseProto.Builder,
+      UpdateNamenodeRegistrationResponseProtoOrBuilder> translator =
+          new FederationProtocolPBTranslator<
+              UpdateNamenodeRegistrationResponseProto,
+              UpdateNamenodeRegistrationResponseProto.Builder,
+              UpdateNamenodeRegistrationResponseProtoOrBuilder>(
+                  UpdateNamenodeRegistrationResponseProto.class);
+
+  public UpdateNamenodeRegistrationResponsePBImpl() {
+  }
+
+  @Override
+  public UpdateNamenodeRegistrationResponseProto getProto() {
+    return this.translator.build();
+  }
+
+  @Override
+  public void setProto(Message proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public void readInstance(String base64String) throws IOException {
+    this.translator.readInstance(base64String);
+  }
+
+  @Override
+  public boolean getResult() {
+    return this.translator.getProtoOrBuilder().getStatus();
+  }
+
+  @Override
+  public void setResult(boolean result) {
+    this.translator.getBuilder().setStatus(result);
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/protocol/impl/pb/package-info.java

@@ -0,0 +1,29 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Protobuf implementations of FederationProtocolBase request/response objects
+ * used by state store APIs. Each state store API is defined in the
+ * org.apache.hadoop.hdfs.server.federation.store.protocol package.
+ */
+@InterfaceAudience.Private
+@InterfaceStability.Evolving
+package org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/records/MembershipState.java

@@ -0,0 +1,329 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.records;
+
+import static org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState.ACTIVE;
+import static org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState.EXPIRED;
+import static org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState.UNAVAILABLE;
+
+import java.io.IOException;
+import java.util.Comparator;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeContext;
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+
+/**
+ * Data schema for storing NN registration information in the
+ * {@link org.apache.hadoop.hdfs.server.federation.store.StateStoreService
+ * FederationStateStoreService}.
+ */
+public abstract class MembershipState extends BaseRecord
+    implements FederationNamenodeContext {
+
+  /** Expiration time in ms for this entry. */
+  private static long expirationMs;
+
+
+  /** Comparator based on the name.*/
+  public static final Comparator<MembershipState> NAME_COMPARATOR =
+      new Comparator<MembershipState>() {
+        public int compare(MembershipState m1, MembershipState m2) {
+          return m1.compareNameTo(m2);
+        }
+      };
+
+
+  /**
+   * Constructors.
+   */
+  public MembershipState() {
+    super();
+  }
+
+  /**
+   * Create a new membership instance.
+   * @return Membership instance.
+   * @throws IOException
+   */
+  public static MembershipState newInstance() {
+    MembershipState record =
+        StateStoreSerializer.newRecord(MembershipState.class);
+    record.init();
+    return record;
+  }
+
+  /**
+   * Create a new membership instance.
+   *
+   * @param router Identifier of the router.
+   * @param nameservice Identifier of the nameservice.
+   * @param namenode Identifier of the namenode.
+   * @param clusterId Identifier of the cluster.
+   * @param blockPoolId Identifier of the blockpool.
+   * @param rpcAddress RPC address.
+   * @param serviceAddress Service RPC address.
+   * @param lifelineAddress Lifeline RPC address.
+   * @param webAddress HTTP address.
+   * @param state State of the federation.
+   * @param safemode If the safe mode is enabled.
+   * @return Membership instance.
+   * @throws IOException If we cannot create the instance.
+   */
+  public static MembershipState newInstance(String router, String nameservice,
+      String namenode, String clusterId, String blockPoolId, String rpcAddress,
+      String serviceAddress, String lifelineAddress, String webAddress,
+      FederationNamenodeServiceState state, boolean safemode) {
+
+    MembershipState record = MembershipState.newInstance();
+    record.setRouterId(router);
+    record.setNameserviceId(nameservice);
+    record.setNamenodeId(namenode);
+    record.setRpcAddress(rpcAddress);
+    record.setServiceAddress(serviceAddress);
+    record.setLifelineAddress(lifelineAddress);
+    record.setWebAddress(webAddress);
+    record.setIsSafeMode(safemode);
+    record.setState(state);
+    record.setClusterId(clusterId);
+    record.setBlockPoolId(blockPoolId);
+    record.validate();
+    return record;
+  }
+
+  public abstract void setRouterId(String routerId);
+
+  public abstract String getRouterId();
+
+  public abstract void setNameserviceId(String nameserviceId);
+
+  public abstract void setNamenodeId(String namenodeId);
+
+  public abstract void setWebAddress(String webAddress);
+
+  public abstract void setRpcAddress(String rpcAddress);
+
+  public abstract void setServiceAddress(String serviceAddress);
+
+  public abstract void setLifelineAddress(String lifelineAddress);
+
+  public abstract void setIsSafeMode(boolean isSafeMode);
+
+  public abstract void setClusterId(String clusterId);
+
+  public abstract void setBlockPoolId(String blockPoolId);
+
+  public abstract void setState(FederationNamenodeServiceState state);
+
+  public abstract String getNameserviceId();
+
+  public abstract String getNamenodeId();
+
+  public abstract String getClusterId();
+
+  public abstract String getBlockPoolId();
+
+  public abstract String getRpcAddress();
+
+  public abstract String getServiceAddress();
+
+  public abstract String getLifelineAddress();
+
+  public abstract String getWebAddress();
+
+  public abstract boolean getIsSafeMode();
+
+  public abstract FederationNamenodeServiceState getState();
+
+  public abstract void setStats(MembershipStats stats);
+
+  public abstract MembershipStats getStats() throws IOException;
+
+  public abstract void setLastContact(long contact);
+
+  public abstract long getLastContact();
+
+  @Override
+  public boolean like(BaseRecord o) {
+    if (o instanceof MembershipState) {
+      MembershipState other = (MembershipState)o;
+      if (getRouterId() != null &&
+          !getRouterId().equals(other.getRouterId())) {
+        return false;
+      }
+      if (getNameserviceId() != null &&
+          !getNameserviceId().equals(other.getNameserviceId())) {
+        return false;
+      }
+      if (getNamenodeId() != null &&
+          !getNamenodeId().equals(other.getNamenodeId())) {
+        return false;
+      }
+      if (getRpcAddress() != null &&
+          !getRpcAddress().equals(other.getRpcAddress())) {
+        return false;
+      }
+      if (getClusterId() != null &&
+          !getClusterId().equals(other.getClusterId())) {
+        return false;
+      }
+      if (getBlockPoolId() != null &&
+          !getBlockPoolId().equals(other.getBlockPoolId())) {
+        return false;
+      }
+      if (getState() != null &&
+          !getState().equals(other.getState())) {
+        return false;
+      }
+      return true;
+    }
+    return false;
+  }
+
+  @Override
+  public String toString() {
+    return getRouterId() + "->" + getNameserviceId() + ":" + getNamenodeId()
+        + ":" + getRpcAddress() + "-" + getState();
+  }
+
+  @Override
+  public SortedMap<String, String> getPrimaryKeys() {
+    SortedMap<String, String> map = new TreeMap<String, String>();
+    map.put("routerId", getRouterId());
+    map.put("nameserviceId", getNameserviceId());
+    map.put("namenodeId", getNamenodeId());
+    return map;
+  }
+
+  /**
+   * Check if the namenode is available.
+   *
+   * @return If the namenode is available.
+   */
+  public boolean isAvailable() {
+    return getState() == ACTIVE;
+  }
+
+  /**
+   * Validates the entry. Throws an IllegalArgementException if the data record
+   * is missing required information.
+   */
+  @Override
+  public boolean validate() {
+    boolean ret = super.validate();
+    if (getNameserviceId() == null || getNameserviceId().length() == 0) {
+      //LOG.error("Invalid registration, no nameservice specified " + this);
+      ret = false;
+    }
+    if (getWebAddress() == null || getWebAddress().length() == 0) {
+      //LOG.error("Invalid registration, no web address specified " + this);
+      ret = false;
+    }
+    if (getRpcAddress() == null || getRpcAddress().length() == 0) {
+      //LOG.error("Invalid registration, no rpc address specified " + this);
+      ret = false;
+    }
+    if (!isBadState() &&
+        (getBlockPoolId().isEmpty() || getBlockPoolId().length() == 0)) {
+      //LOG.error("Invalid registration, no block pool specified " + this);
+      ret = false;
+    }
+    return ret;
+  }
+
+
+  /**
+   * Overrides the cached getBlockPoolId() with an update. The state will be
+   * reset when the cache is flushed
+   *
+   * @param newState Service state of the namenode.
+   */
+  public void overrideState(FederationNamenodeServiceState newState) {
+    this.setState(newState);
+  }
+
+  /**
+   * Sort by nameservice, namenode, and router.
+   *
+   * @param other Another membership to compare to.
+   * @return If this object goes before the parameter.
+   */
+  public int compareNameTo(MembershipState other) {
+    int ret = this.getNameserviceId().compareTo(other.getNameserviceId());
+    if (ret == 0) {
+      ret = this.getNamenodeId().compareTo(other.getNamenodeId());
+    }
+    if (ret == 0) {
+      ret = this.getRouterId().compareTo(other.getRouterId());
+    }
+    return ret;
+  }
+
+  /**
+   * Get the identifier of this namenode registration.
+   * @return Identifier of the namenode.
+   */
+  public String getNamenodeKey() {
+    return getNamenodeKey(this.getNameserviceId(), this.getNamenodeId());
+  }
+
+  /**
+   * Generate the identifier for a Namenode in the HDFS federation.
+   *
+   * @param nsId Nameservice of the Namenode.
+   * @param nnId Namenode within the Nameservice (HA).
+   * @return Namenode identifier within the federation.
+   */
+  public static String getNamenodeKey(String nsId, String nnId) {
+    return nsId + "-" + nnId;
+  }
+
+  /**
+   * Check if the membership is in a bad state (expired or unavailable).
+   * @return If the membership is in a bad state (expired or unavailable).
+   */
+  private boolean isBadState() {
+    return this.getState() == EXPIRED || this.getState() == UNAVAILABLE;
+  }
+
+  @Override
+  public boolean checkExpired(long currentTime) {
+    if (super.checkExpired(currentTime)) {
+      this.setState(EXPIRED);
+      // Commit it
+      return true;
+    }
+    return false;
+  }
+
+  @Override
+  public long getExpirationMs() {
+    return MembershipState.expirationMs;
+  }
+
+  /**
+   * Set the expiration time for this class.
+   *
+   * @param time Expiration time in milliseconds.
+   */
+  public static void setExpirationMs(long time) {
+    MembershipState.expirationMs = time;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/records/MembershipStats.java

@@ -0,0 +1,126 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.records;
+
+import java.io.IOException;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+
+/**
+ * Data schema for storing NN stats in the
+ * {@link org.apache.hadoop.hdfs.server.federation.store.StateStoreService
+ * StateStoreService}.
+ */
+public abstract class MembershipStats extends BaseRecord {
+
+  public static MembershipStats newInstance() throws IOException {
+    MembershipStats record =
+        StateStoreSerializer.newRecord(MembershipStats.class);
+    record.init();
+    return record;
+  }
+
+  public abstract void setTotalSpace(long space);
+
+  public abstract long getTotalSpace();
+
+  public abstract void setAvailableSpace(long space);
+
+  public abstract long getAvailableSpace();
+
+  public abstract void setNumOfFiles(long files);
+
+  public abstract long getNumOfFiles();
+
+  public abstract void setNumOfBlocks(long blocks);
+
+  public abstract long getNumOfBlocks();
+
+  public abstract void setNumOfBlocksMissing(long blocks);
+
+  public abstract long getNumOfBlocksMissing();
+
+  public abstract void setNumOfBlocksPendingReplication(long blocks);
+
+  public abstract long getNumOfBlocksPendingReplication();
+
+  public abstract void setNumOfBlocksUnderReplicated(long blocks);
+
+  public abstract long getNumOfBlocksUnderReplicated();
+
+  public abstract void setNumOfBlocksPendingDeletion(long blocks);
+
+  public abstract long getNumOfBlocksPendingDeletion();
+
+  public abstract void setNumOfActiveDatanodes(int nodes);
+
+  public abstract int getNumOfActiveDatanodes();
+
+  public abstract void setNumOfDeadDatanodes(int nodes);
+
+  public abstract int getNumOfDeadDatanodes();
+
+  public abstract void setNumOfDecommissioningDatanodes(int nodes);
+
+  public abstract int getNumOfDecommissioningDatanodes();
+
+  public abstract void setNumOfDecomActiveDatanodes(int nodes);
+
+  public abstract int getNumOfDecomActiveDatanodes();
+
+  public abstract void setNumOfDecomDeadDatanodes(int nodes);
+
+  public abstract int getNumOfDecomDeadDatanodes();
+
+  @Override
+  public SortedMap<String, String> getPrimaryKeys() {
+    // This record is not stored directly, no key needed
+    SortedMap<String, String> map = new TreeMap<String, String>();
+    return map;
+  }
+
+  @Override
+  public long getExpirationMs() {
+    // This record is not stored directly, no expiration needed
+    return -1;
+  }
+
+  @Override
+  public void setDateModified(long time) {
+    // We don't store this record directly
+  }
+
+  @Override
+  public long getDateModified() {
+    // We don't store this record directly
+    return 0;
+  }
+
+  @Override
+  public void setDateCreated(long time) {
+    // We don't store this record directly
+  }
+
+  @Override
+  public long getDateCreated() {
+    // We don't store this record directly
+    return 0;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/records/impl/pb/MembershipStatePBImpl.java

@@ -0,0 +1,334 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.records.impl.pb;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeMembershipRecordProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeMembershipRecordProto.Builder;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeMembershipRecordProtoOrBuilder;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeMembershipStatsRecordProto;
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.FederationProtocolPBTranslator;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipStats;
+
+import com.google.protobuf.Message;
+
+/**
+ * Protobuf implementation of the MembershipState record.
+ */
+public class MembershipStatePBImpl extends MembershipState implements PBRecord {
+
+  private FederationProtocolPBTranslator<NamenodeMembershipRecordProto, Builder,
+      NamenodeMembershipRecordProtoOrBuilder> translator =
+          new FederationProtocolPBTranslator<NamenodeMembershipRecordProto,
+              Builder, NamenodeMembershipRecordProtoOrBuilder>(
+                  NamenodeMembershipRecordProto.class);
+
+  public MembershipStatePBImpl() {
+  }
+
+  public MembershipStatePBImpl(NamenodeMembershipRecordProto proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public NamenodeMembershipRecordProto getProto() {
+    return this.translator.build();
+  }
+
+  @Override
+  public void setProto(Message proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public void readInstance(String base64String) throws IOException {
+    this.translator.readInstance(base64String);
+  }
+
+  @Override
+  public void setRouterId(String routerId) {
+    Builder builder = this.translator.getBuilder();
+    if (routerId == null) {
+      builder.clearRouterId();
+    } else {
+      builder.setRouterId(routerId);
+    }
+  }
+
+  @Override
+  public void setNameserviceId(String nameserviceId) {
+    Builder builder = this.translator.getBuilder();
+    if (nameserviceId == null) {
+      builder.clearNameserviceId();
+    } else {
+      builder.setNameserviceId(nameserviceId);
+    }
+  }
+
+  @Override
+  public void setNamenodeId(String namenodeId) {
+    Builder builder = this.translator.getBuilder();
+    if (namenodeId == null) {
+      builder.clearNamenodeId();
+    } else {
+      builder.setNamenodeId(namenodeId);
+    }
+  }
+
+  @Override
+  public void setWebAddress(String webAddress) {
+    Builder builder = this.translator.getBuilder();
+    if (webAddress == null) {
+      builder.clearWebAddress();
+    } else {
+      builder.setWebAddress(webAddress);
+    }
+  }
+
+  @Override
+  public void setRpcAddress(String rpcAddress) {
+    Builder builder = this.translator.getBuilder();
+    if (rpcAddress == null) {
+      builder.clearRpcAddress();
+    } else {
+      builder.setRpcAddress(rpcAddress);
+    }
+  }
+
+  @Override
+  public void setServiceAddress(String serviceAddress) {
+    this.translator.getBuilder().setServiceAddress(serviceAddress);
+  }
+
+  @Override
+  public void setLifelineAddress(String lifelineAddress) {
+    Builder builder = this.translator.getBuilder();
+    if (lifelineAddress == null) {
+      builder.clearLifelineAddress();
+    } else {
+      builder.setLifelineAddress(lifelineAddress);
+    }
+  }
+
+  @Override
+  public void setIsSafeMode(boolean isSafeMode) {
+    Builder builder = this.translator.getBuilder();
+    builder.setIsSafeMode(isSafeMode);
+  }
+
+  @Override
+  public void setClusterId(String clusterId) {
+    Builder builder = this.translator.getBuilder();
+    if (clusterId == null) {
+      builder.clearClusterId();
+    } else {
+      builder.setClusterId(clusterId);
+    }
+  }
+
+  @Override
+  public void setBlockPoolId(String blockPoolId) {
+    Builder builder = this.translator.getBuilder();
+    if (blockPoolId == null) {
+      builder.clearBlockPoolId();
+    } else {
+      builder.setBlockPoolId(blockPoolId);
+    }
+  }
+
+  @Override
+  public void setState(FederationNamenodeServiceState state) {
+    Builder builder = this.translator.getBuilder();
+    if (state == null) {
+      builder.clearState();
+    } else {
+      builder.setState(state.toString());
+    }
+  }
+
+  @Override
+  public String getRouterId() {
+    NamenodeMembershipRecordProtoOrBuilder proto =
+        this.translator.getProtoOrBuilder();
+    if (!proto.hasRouterId()) {
+      return null;
+    }
+    return proto.getRouterId();
+  }
+
+  @Override
+  public String getNameserviceId() {
+    NamenodeMembershipRecordProtoOrBuilder proto =
+        this.translator.getProtoOrBuilder();
+    if (!proto.hasNameserviceId()) {
+      return null;
+    }
+    return this.translator.getProtoOrBuilder().getNameserviceId();
+  }
+
+  @Override
+  public String getNamenodeId() {
+    NamenodeMembershipRecordProtoOrBuilder proto =
+        this.translator.getProtoOrBuilder();
+    if (!proto.hasNamenodeId()) {
+      return null;
+    }
+    return this.translator.getProtoOrBuilder().getNamenodeId();
+  }
+
+  @Override
+  public String getClusterId() {
+    NamenodeMembershipRecordProtoOrBuilder proto =
+        this.translator.getProtoOrBuilder();
+    if (!proto.hasClusterId()) {
+      return null;
+    }
+    return this.translator.getProtoOrBuilder().getClusterId();
+  }
+
+  @Override
+  public String getBlockPoolId() {
+    NamenodeMembershipRecordProtoOrBuilder proto =
+        this.translator.getProtoOrBuilder();
+    if (!proto.hasBlockPoolId()) {
+      return null;
+    }
+    return this.translator.getProtoOrBuilder().getBlockPoolId();
+  }
+
+  @Override
+  public String getRpcAddress() {
+    NamenodeMembershipRecordProtoOrBuilder proto =
+        this.translator.getProtoOrBuilder();
+    if (!proto.hasRpcAddress()) {
+      return null;
+    }
+    return this.translator.getProtoOrBuilder().getRpcAddress();
+  }
+
+  @Override
+  public String getServiceAddress() {
+    NamenodeMembershipRecordProtoOrBuilder proto =
+        this.translator.getProtoOrBuilder();
+    if (!proto.hasServiceAddress()) {
+      return null;
+    }
+    return this.translator.getProtoOrBuilder().getServiceAddress();
+  }
+
+  @Override
+  public String getWebAddress() {
+    NamenodeMembershipRecordProtoOrBuilder proto =
+        this.translator.getProtoOrBuilder();
+    if (!proto.hasWebAddress()) {
+      return null;
+    }
+    return this.translator.getProtoOrBuilder().getWebAddress();
+  }
+
+  @Override
+  public String getLifelineAddress() {
+    NamenodeMembershipRecordProtoOrBuilder proto =
+        this.translator.getProtoOrBuilder();
+    if (!proto.hasLifelineAddress()) {
+      return null;
+    }
+    return this.translator.getProtoOrBuilder().getLifelineAddress();
+  }
+
+  @Override
+  public boolean getIsSafeMode() {
+    return this.translator.getProtoOrBuilder().getIsSafeMode();
+  }
+
+  @Override
+  public FederationNamenodeServiceState getState() {
+    FederationNamenodeServiceState ret =
+        FederationNamenodeServiceState.UNAVAILABLE;
+    NamenodeMembershipRecordProtoOrBuilder proto =
+        this.translator.getProtoOrBuilder();
+    if (!proto.hasState()) {
+      return null;
+    }
+    try {
+      ret = FederationNamenodeServiceState.valueOf(proto.getState());
+    } catch (IllegalArgumentException e) {
+      // Ignore this error
+    }
+    return ret;
+  }
+
+  @Override
+  public void setStats(MembershipStats stats) {
+    if (stats instanceof MembershipStatsPBImpl) {
+      MembershipStatsPBImpl statsPB = (MembershipStatsPBImpl)stats;
+      NamenodeMembershipStatsRecordProto statsProto =
+          (NamenodeMembershipStatsRecordProto)statsPB.getProto();
+      this.translator.getBuilder().setStats(statsProto);
+    }
+  }
+
+  @Override
+  public MembershipStats getStats() throws IOException {
+    NamenodeMembershipStatsRecordProto statsProto =
+        this.translator.getProtoOrBuilder().getStats();
+    MembershipStats stats =
+        StateStoreSerializer.newRecord(MembershipStats.class);
+    if (stats instanceof MembershipStatsPBImpl) {
+      MembershipStatsPBImpl statsPB = (MembershipStatsPBImpl)stats;
+      statsPB.setProto(statsProto);
+      return statsPB;
+    } else {
+      throw new IOException("Cannot get stats for the membership");
+    }
+  }
+
+  @Override
+  public void setLastContact(long contact) {
+    this.translator.getBuilder().setLastContact(contact);
+  }
+
+  @Override
+  public long getLastContact() {
+    return this.translator.getProtoOrBuilder().getLastContact();
+  }
+
+  @Override
+  public void setDateModified(long time) {
+    this.translator.getBuilder().setDateModified(time);
+  }
+
+  @Override
+  public long getDateModified() {
+    return this.translator.getProtoOrBuilder().getDateModified();
+  }
+
+  @Override
+  public void setDateCreated(long time) {
+    this.translator.getBuilder().setDateCreated(time);
+  }
+
+  @Override
+  public long getDateCreated() {
+    return this.translator.getProtoOrBuilder().getDateCreated();
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/federation/store/records/impl/pb/MembershipStatsPBImpl.java

@@ -0,0 +1,191 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.records.impl.pb;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeMembershipStatsRecordProto;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeMembershipStatsRecordProto.Builder;
+import org.apache.hadoop.hdfs.federation.protocol.proto.HdfsServerFederationProtos.NamenodeMembershipStatsRecordProtoOrBuilder;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.impl.pb.FederationProtocolPBTranslator;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipStats;
+
+import com.google.protobuf.Message;
+
+/**
+ * Protobuf implementation of the MembershipStats record.
+ */
+public class MembershipStatsPBImpl extends MembershipStats
+    implements PBRecord {
+
+  private FederationProtocolPBTranslator<NamenodeMembershipStatsRecordProto,
+      Builder, NamenodeMembershipStatsRecordProtoOrBuilder> translator =
+          new FederationProtocolPBTranslator<NamenodeMembershipStatsRecordProto,
+          Builder, NamenodeMembershipStatsRecordProtoOrBuilder>(
+              NamenodeMembershipStatsRecordProto.class);
+
+  public MembershipStatsPBImpl() {
+  }
+
+  @Override
+  public NamenodeMembershipStatsRecordProto getProto() {
+    return this.translator.build();
+  }
+
+  @Override
+  public void setProto(Message proto) {
+    this.translator.setProto(proto);
+  }
+
+  @Override
+  public void readInstance(String base64String) throws IOException {
+    this.translator.readInstance(base64String);
+  }
+
+  @Override
+  public void setTotalSpace(long space) {
+    this.translator.getBuilder().setTotalSpace(space);
+  }
+
+  @Override
+  public long getTotalSpace() {
+    return this.translator.getProtoOrBuilder().getTotalSpace();
+  }
+
+  @Override
+  public void setAvailableSpace(long space) {
+    this.translator.getBuilder().setAvailableSpace(space);
+  }
+
+  @Override
+  public long getAvailableSpace() {
+    return this.translator.getProtoOrBuilder().getAvailableSpace();
+  }
+
+  @Override
+  public void setNumOfFiles(long files) {
+    this.translator.getBuilder().setNumOfFiles(files);
+  }
+
+  @Override
+  public long getNumOfFiles() {
+    return this.translator.getProtoOrBuilder().getNumOfFiles();
+  }
+
+  @Override
+  public void setNumOfBlocks(long blocks) {
+    this.translator.getBuilder().setNumOfBlocks(blocks);
+  }
+
+  @Override
+  public long getNumOfBlocks() {
+    return this.translator.getProtoOrBuilder().getNumOfBlocks();
+  }
+
+  @Override
+  public void setNumOfBlocksMissing(long blocks) {
+    this.translator.getBuilder().setNumOfBlocksMissing(blocks);
+  }
+
+  @Override
+  public long getNumOfBlocksMissing() {
+    return this.translator.getProtoOrBuilder().getNumOfBlocksMissing();
+  }
+
+  @Override
+  public void setNumOfBlocksPendingReplication(long blocks) {
+    this.translator.getBuilder().setNumOfBlocksPendingReplication(blocks);
+  }
+
+  @Override
+  public long getNumOfBlocksPendingReplication() {
+    return this.translator.getProtoOrBuilder()
+        .getNumOfBlocksPendingReplication();
+  }
+
+  @Override
+  public void setNumOfBlocksUnderReplicated(long blocks) {
+    this.translator.getBuilder().setNumOfBlocksUnderReplicated(blocks);
+  }
+
+  @Override
+  public long getNumOfBlocksUnderReplicated() {
+    return this.translator.getProtoOrBuilder().getNumOfBlocksUnderReplicated();
+  }
+
+  @Override
+  public void setNumOfBlocksPendingDeletion(long blocks) {
+    this.translator.getBuilder().setNumOfBlocksPendingDeletion(blocks);
+  }
+
+  @Override
+  public long getNumOfBlocksPendingDeletion() {
+    return this.translator.getProtoOrBuilder().getNumOfBlocksPendingDeletion();
+  }
+
+  @Override
+  public void setNumOfActiveDatanodes(int nodes) {
+    this.translator.getBuilder().setNumOfActiveDatanodes(nodes);
+  }
+
+  @Override
+  public int getNumOfActiveDatanodes() {
+    return this.translator.getProtoOrBuilder().getNumOfActiveDatanodes();
+  }
+
+  @Override
+  public void setNumOfDeadDatanodes(int nodes) {
+    this.translator.getBuilder().setNumOfDeadDatanodes(nodes);
+  }
+
+  @Override
+  public int getNumOfDeadDatanodes() {
+    return this.translator.getProtoOrBuilder().getNumOfDeadDatanodes();
+  }
+
+  @Override
+  public void setNumOfDecommissioningDatanodes(int nodes) {
+    this.translator.getBuilder().setNumOfDecommissioningDatanodes(nodes);
+  }
+
+  @Override
+  public int getNumOfDecommissioningDatanodes() {
+    return this.translator.getProtoOrBuilder()
+        .getNumOfDecommissioningDatanodes();
+  }
+
+  @Override
+  public void setNumOfDecomActiveDatanodes(int nodes) {
+    this.translator.getBuilder().setNumOfDecomActiveDatanodes(nodes);
+  }
+
+  @Override
+  public int getNumOfDecomActiveDatanodes() {
+    return this.translator.getProtoOrBuilder().getNumOfDecomActiveDatanodes();
+  }
+
+  @Override
+  public void setNumOfDecomDeadDatanodes(int nodes) {
+    this.translator.getBuilder().setNumOfDecomDeadDatanodes(nodes);
+  }
+
+  @Override
+  public int getNumOfDecomDeadDatanodes() {
+    return this.translator.getProtoOrBuilder().getNumOfDecomDeadDatanodes();
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/proto/FederationProtocol.proto

@@ -0,0 +1,107 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+option java_package = "org.apache.hadoop.hdfs.federation.protocol.proto";
+option java_outer_classname = "HdfsServerFederationProtos";
+option java_generic_services = true;
+option java_generate_equals_and_hash = true;
+package hadoop.hdfs;
+
+
+/////////////////////////////////////////////////
+// Membership
+/////////////////////////////////////////////////
+
+message NamenodeMembershipStatsRecordProto {
+  optional uint64 totalSpace = 1;
+  optional uint64 availableSpace = 2;
+
+  optional uint64 numOfFiles = 10;
+  optional uint64 numOfBlocks = 11;
+  optional uint64 numOfBlocksMissing = 12;
+  optional uint64 numOfBlocksPendingReplication = 13;
+  optional uint64 numOfBlocksUnderReplicated = 14;
+  optional uint64 numOfBlocksPendingDeletion = 15;
+
+  optional uint32 numOfActiveDatanodes = 20;
+  optional uint32 numOfDeadDatanodes = 21;
+  optional uint32 numOfDecommissioningDatanodes = 22;
+  optional uint32 numOfDecomActiveDatanodes = 23;
+  optional uint32 numOfDecomDeadDatanodes = 24;
+}
+
+message NamenodeMembershipRecordProto {
+  optional uint64 dateCreated = 1;
+  optional uint64 dateModified = 2;
+  optional uint64 lastContact = 3;
+  optional string routerId = 4;
+  optional string nameserviceId = 5;
+  optional string namenodeId = 6;
+  optional string clusterId = 7;
+  optional string blockPoolId = 8;
+  optional string webAddress = 9;
+  optional string rpcAddress = 10;
+  optional string serviceAddress = 11;
+  optional string lifelineAddress = 12;
+  optional string state = 13;
+  optional bool isSafeMode = 14;
+
+  optional NamenodeMembershipStatsRecordProto stats = 15;
+}
+
+message FederationNamespaceInfoProto {
+  optional string blockPoolId = 1;
+  optional string clusterId = 2;
+  optional string nameserviceId = 3;
+}
+
+message GetNamenodeRegistrationsRequestProto {
+  optional NamenodeMembershipRecordProto membership = 1;
+}
+
+message GetNamenodeRegistrationsResponseProto {
+  repeated NamenodeMembershipRecordProto namenodeMemberships = 1;
+}
+
+message GetExpiredRegistrationsRequestProto {
+}
+
+message GetNamespaceInfoRequestProto {
+}
+
+message GetNamespaceInfoResponseProto {
+  repeated FederationNamespaceInfoProto namespaceInfos = 1;
+}
+
+message UpdateNamenodeRegistrationRequestProto {
+  optional string nameserviceId = 1;
+  optional string namenodeId = 2;
+  optional string state = 3;
+}
+
+message UpdateNamenodeRegistrationResponseProto {
+  optional bool status = 1;
+}
+
+message NamenodeHeartbeatRequestProto {
+  optional NamenodeMembershipRecordProto namenodeMembership = 1;
+}
+
+message NamenodeHeartbeatResponseProto {
+  optional bool status = 1;
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

@@ -4755,7 +4755,7 @@
 
   <property>
     <name>dfs.federation.router.namenode.resolver.client.class</name>
-    <value>org.apache.hadoop.hdfs.server.federation.MockResolver</value>
+    <value>org.apache.hadoop.hdfs.server.federation.resolver.MembershipNamenodeResolver</value>
     <description>
       Class to resolve the namenode for a subcluster.
     </description>
@@ -4785,4 +4785,20 @@
     </description>
   </property>
 
+  <property>
+    <name>dfs.federation.router.cache.ttl</name>
+    <value>60000</value>
+    <description>
+      How often to refresh the State Store caches in milliseconds.
+    </description>
+  </property>
+
+  <property>
+    <name>dfs.federation.router.store.membership.expiration</name>
+    <value>300000</value>
+    <description>
+      Expiration time in milliseconds for a membership record.
+    </description>
+  </property>
+
 </configuration>

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/federation/resolver/TestNamenodeResolver.java

@@ -0,0 +1,284 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.resolver;
+
+import static org.apache.hadoop.hdfs.server.federation.FederationTestUtils.NAMENODES;
+import static org.apache.hadoop.hdfs.server.federation.FederationTestUtils.NAMESERVICES;
+import static org.apache.hadoop.hdfs.server.federation.FederationTestUtils.ROUTERS;
+import static org.apache.hadoop.hdfs.server.federation.FederationTestUtils.createNamenodeReport;
+import static org.apache.hadoop.hdfs.server.federation.FederationTestUtils.verifyException;
+import static org.apache.hadoop.hdfs.server.federation.store.FederationStateStoreTestUtils.clearRecords;
+import static org.apache.hadoop.hdfs.server.federation.store.FederationStateStoreTestUtils.getStateStoreConfiguration;
+import static org.apache.hadoop.hdfs.server.federation.store.FederationStateStoreTestUtils.newStateStore;
+import static org.apache.hadoop.hdfs.server.federation.store.FederationStateStoreTestUtils.waitStateStore;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.ha.HAServiceProtocol.HAServiceState;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.server.federation.store.StateStoreService;
+import org.apache.hadoop.hdfs.server.federation.store.StateStoreUnavailableException;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+import org.junit.AfterClass;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+/**
+ * Test the basic {@link ActiveNamenodeResolver} functionality.
+ */
+public class TestNamenodeResolver {
+
+  private static StateStoreService stateStore;
+  private static ActiveNamenodeResolver namenodeResolver;
+
+  @BeforeClass
+  public static void create() throws Exception {
+
+    Configuration conf = getStateStoreConfiguration();
+
+    // Reduce expirations to 5 seconds
+    conf.setLong(
+        DFSConfigKeys.FEDERATION_STORE_MEMBERSHIP_EXPIRATION_MS,
+        TimeUnit.SECONDS.toMillis(5));
+
+    stateStore = newStateStore(conf);
+    assertNotNull(stateStore);
+
+    namenodeResolver = new MembershipNamenodeResolver(conf, stateStore);
+    namenodeResolver.setRouterId(ROUTERS[0]);
+  }
+
+  @AfterClass
+  public static void destroy() throws Exception {
+    stateStore.stop();
+    stateStore.close();
+  }
+
+  @Before
+  public void setup() throws IOException, InterruptedException {
+    // Wait for state store to connect
+    stateStore.loadDriver();
+    waitStateStore(stateStore, 10000);
+
+    // Clear NN registrations
+    boolean cleared = clearRecords(stateStore, MembershipState.class);
+    assertTrue(cleared);
+  }
+
+  @Test
+  public void testStateStoreDisconnected() throws Exception {
+
+    // Add an entry to the store
+    NamenodeStatusReport report = createNamenodeReport(
+        NAMESERVICES[0], NAMENODES[0], HAServiceState.ACTIVE);
+    assertTrue(namenodeResolver.registerNamenode(report));
+
+    // Close the data store driver
+    stateStore.closeDriver();
+    assertFalse(stateStore.isDriverReady());
+
+    // Flush the caches
+    stateStore.refreshCaches(true);
+
+    // Verify commands fail due to no cached data and no state store
+    // connectivity.
+    List<? extends FederationNamenodeContext> nns =
+        namenodeResolver.getNamenodesForBlockPoolId(NAMESERVICES[0]);
+    assertNull(nns);
+
+    verifyException(namenodeResolver, "registerNamenode",
+        StateStoreUnavailableException.class,
+        new Class[] {NamenodeStatusReport.class}, new Object[] {report});
+  }
+
+  /**
+   * Verify the first registration on the resolver.
+   *
+   * @param nsId Nameservice identifier.
+   * @param nnId Namenode identifier within the nemeservice.
+   * @param resultsCount Number of results expected.
+   * @param state Expected state for the first one.
+   * @throws IOException If we cannot get the namenodes.
+   */
+  private void verifyFirstRegistration(String nsId, String nnId,
+      int resultsCount, FederationNamenodeServiceState state)
+          throws IOException {
+    List<? extends FederationNamenodeContext> namenodes =
+        namenodeResolver.getNamenodesForNameserviceId(nsId);
+    if (resultsCount == 0) {
+      assertNull(namenodes);
+    } else {
+      assertEquals(resultsCount, namenodes.size());
+      if (namenodes.size() > 0) {
+        FederationNamenodeContext namenode = namenodes.get(0);
+        assertEquals(state, namenode.getState());
+        assertEquals(nnId, namenode.getNamenodeId());
+      }
+    }
+  }
+
+  @Test
+  public void testRegistrationExpired()
+      throws InterruptedException, IOException {
+
+    // Populate the state store with a single NN element
+    // 1) ns0:nn0 - Active
+    // Wait for the entry to expire without heartbeating
+    // Verify the NN entry is not accessible once expired.
+    NamenodeStatusReport report = createNamenodeReport(
+        NAMESERVICES[0], NAMENODES[0], HAServiceState.ACTIVE);
+    assertTrue(namenodeResolver.registerNamenode(report));
+
+    // Load cache
+    stateStore.refreshCaches(true);
+
+    // Verify
+    verifyFirstRegistration(
+        NAMESERVICES[0], NAMENODES[0], 1,
+        FederationNamenodeServiceState.ACTIVE);
+
+    // Wait past expiration (set in conf to 5 seconds)
+    Thread.sleep(6000);
+    // Reload cache
+    stateStore.refreshCaches(true);
+
+    // Verify entry is now expired and is no longer in the cache
+    verifyFirstRegistration(
+        NAMESERVICES[0], NAMENODES[0], 0,
+        FederationNamenodeServiceState.ACTIVE);
+
+    // Heartbeat again, updates dateModified
+    assertTrue(namenodeResolver.registerNamenode(report));
+    // Reload cache
+    stateStore.refreshCaches(true);
+
+    // Verify updated entry is marked active again and accessible to RPC server
+    verifyFirstRegistration(
+        NAMESERVICES[0], NAMENODES[0], 1,
+        FederationNamenodeServiceState.ACTIVE);
+  }
+
+  @Test
+  public void testRegistrationNamenodeSelection()
+      throws InterruptedException, IOException {
+
+    // 1) ns0:nn0 - Active
+    // 2) ns0:nn1 - Standby (newest)
+    // Verify the selected entry is the active entry
+    assertTrue(namenodeResolver.registerNamenode(
+        createNamenodeReport(
+            NAMESERVICES[0], NAMENODES[0], HAServiceState.ACTIVE)));
+    Thread.sleep(100);
+    assertTrue(namenodeResolver.registerNamenode(
+        createNamenodeReport(
+            NAMESERVICES[0], NAMENODES[1], HAServiceState.STANDBY)));
+
+    stateStore.refreshCaches(true);
+
+    verifyFirstRegistration(
+        NAMESERVICES[0], NAMENODES[0], 2,
+        FederationNamenodeServiceState.ACTIVE);
+
+    // 1) ns0:nn0 - Expired (stale)
+    // 2) ns0:nn1 - Standby (newest)
+    // Verify the selected entry is the standby entry as the active entry is
+    // stale
+    assertTrue(namenodeResolver.registerNamenode(
+        createNamenodeReport(
+            NAMESERVICES[0], NAMENODES[0], HAServiceState.ACTIVE)));
+
+    // Expire active registration
+    Thread.sleep(6000);
+
+    // Refresh standby registration
+    assertTrue(namenodeResolver.registerNamenode(createNamenodeReport(
+        NAMESERVICES[0], NAMENODES[1], HAServiceState.STANDBY)));
+
+    // Verify that standby is selected (active is now expired)
+    stateStore.refreshCaches(true);
+    verifyFirstRegistration(NAMESERVICES[0], NAMENODES[1], 1,
+        FederationNamenodeServiceState.STANDBY);
+
+    // 1) ns0:nn0 - Active
+    // 2) ns0:nn1 - Unavailable (newest)
+    // Verify the selected entry is the active entry
+    assertTrue(namenodeResolver.registerNamenode(createNamenodeReport(
+        NAMESERVICES[0], NAMENODES[0], HAServiceState.ACTIVE)));
+    Thread.sleep(100);
+    assertTrue(namenodeResolver.registerNamenode(createNamenodeReport(
+        NAMESERVICES[0], NAMENODES[1], null)));
+    stateStore.refreshCaches(true);
+    verifyFirstRegistration(NAMESERVICES[0], NAMENODES[0], 2,
+        FederationNamenodeServiceState.ACTIVE);
+
+    // 1) ns0:nn0 - Unavailable (newest)
+    // 2) ns0:nn1 - Standby
+    // Verify the selected entry is the standby entry
+    assertTrue(namenodeResolver.registerNamenode(createNamenodeReport(
+        NAMESERVICES[0], NAMENODES[1], HAServiceState.STANDBY)));
+    Thread.sleep(1000);
+    assertTrue(namenodeResolver.registerNamenode(createNamenodeReport(
+        NAMESERVICES[0], NAMENODES[0], null)));
+
+    stateStore.refreshCaches(true);
+    verifyFirstRegistration(NAMESERVICES[0], NAMENODES[1], 2,
+        FederationNamenodeServiceState.STANDBY);
+
+    // 1) ns0:nn0 - Active (oldest)
+    // 2) ns0:nn1 - Standby
+    // 3) ns0:nn2 - Active (newest)
+    // Verify the selected entry is the newest active entry
+    assertTrue(namenodeResolver.registerNamenode(
+        createNamenodeReport(NAMESERVICES[0], NAMENODES[0], null)));
+    Thread.sleep(100);
+    assertTrue(namenodeResolver.registerNamenode(createNamenodeReport(
+        NAMESERVICES[0], NAMENODES[1], HAServiceState.STANDBY)));
+    Thread.sleep(100);
+    assertTrue(namenodeResolver.registerNamenode(createNamenodeReport(
+        NAMESERVICES[0], NAMENODES[2], HAServiceState.ACTIVE)));
+
+    stateStore.refreshCaches(true);
+    verifyFirstRegistration(NAMESERVICES[0], NAMENODES[2], 3,
+        FederationNamenodeServiceState.ACTIVE);
+
+    // 1) ns0:nn0 - Standby (oldest)
+    // 2) ns0:nn1 - Standby (newest)
+    // 3) ns0:nn2 - Standby
+    // Verify the selected entry is the newest standby entry
+    assertTrue(namenodeResolver.registerNamenode(createNamenodeReport(
+        NAMESERVICES[0], NAMENODES[0], HAServiceState.STANDBY)));
+    assertTrue(namenodeResolver.registerNamenode(createNamenodeReport(
+        NAMESERVICES[0], NAMENODES[2], HAServiceState.STANDBY)));
+    Thread.sleep(1500);
+    assertTrue(namenodeResolver.registerNamenode(createNamenodeReport(
+        NAMESERVICES[0], NAMENODES[1], HAServiceState.STANDBY)));
+
+    stateStore.refreshCaches(true);
+    verifyFirstRegistration(NAMESERVICES[0], NAMENODES[1], 3,
+        FederationNamenodeServiceState.STANDBY);
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/federation/store/FederationStateStoreTestUtils.java

@@ -34,9 +34,12 @@
 import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.HdfsConfiguration;
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState;
 import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreDriver;
 import org.apache.hadoop.hdfs.server.federation.store.driver.impl.StateStoreFileBaseImpl;
 import org.apache.hadoop.hdfs.server.federation.store.records.BaseRecord;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipStats;
 import org.apache.hadoop.util.Time;
 
 /**
@@ -96,7 +99,7 @@ public static Configuration getStateStoreConfiguration(
    * @throws IOException If it cannot create the State Store.
    * @throws InterruptedException If we cannot wait for the store to start.
    */
-  public static StateStoreService getStateStore(
+  public static StateStoreService newStateStore(
       Configuration configuration) throws IOException, InterruptedException {
 
     StateStoreService stateStore = new StateStoreService();
@@ -205,6 +208,7 @@ public static <T extends BaseRecord> boolean clearRecords(
     if (!synchronizeRecords(store, emptyList, recordClass)) {
       return false;
     }
+    store.refreshCaches(true);
     return true;
   }
 
@@ -229,4 +233,21 @@ public static <T extends BaseRecord> boolean synchronizeRecords(
     }
     return false;
   }
+
+  public static MembershipState createMockRegistrationForNamenode(
+      String nameserviceId, String namenodeId,
+      FederationNamenodeServiceState state) throws IOException {
+    MembershipState entry = MembershipState.newInstance(
+        "routerId", nameserviceId, namenodeId, "clusterId", "test",
+        "0.0.0.0:0", "0.0.0.0:0", "0.0.0.0:0", "0.0.0.0:0", state, false);
+    MembershipStats stats = MembershipStats.newInstance();
+    stats.setNumOfActiveDatanodes(100);
+    stats.setNumOfDeadDatanodes(10);
+    stats.setNumOfDecommissioningDatanodes(20);
+    stats.setNumOfDecomActiveDatanodes(15);
+    stats.setNumOfDecomDeadDatanodes(5);
+    stats.setNumOfBlocks(10);
+    entry.setStats(stats);
+    return entry;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/federation/store/TestStateStoreBase.java

@@ -0,0 +1,81 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store;
+
+import static org.apache.hadoop.hdfs.server.federation.store.FederationStateStoreTestUtils.newStateStore;
+import static org.apache.hadoop.hdfs.server.federation.store.FederationStateStoreTestUtils.getStateStoreConfiguration;
+import static org.apache.hadoop.hdfs.server.federation.store.FederationStateStoreTestUtils.waitStateStore;
+import static org.junit.Assert.assertNotNull;
+
+import java.io.IOException;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.junit.AfterClass;
+import org.junit.Before;
+import org.junit.BeforeClass;
+
+/**
+ * Test the basic {@link StateStoreService} {@link MountTableStore}
+ * functionality.
+ */
+public class TestStateStoreBase {
+
+  private static StateStoreService stateStore;
+  private static Configuration conf;
+
+  protected static StateStoreService getStateStore() {
+    return stateStore;
+  }
+
+  protected static Configuration getConf() {
+    return conf;
+  }
+
+  @BeforeClass
+  public static void createBase() throws IOException, InterruptedException {
+
+    conf = getStateStoreConfiguration();
+
+    // Disable auto-reconnect to data store
+    conf.setLong(DFSConfigKeys.FEDERATION_STORE_CONNECTION_TEST_MS,
+        TimeUnit.HOURS.toMillis(1));
+  }
+
+  @AfterClass
+  public static void destroyBase() throws Exception {
+    if (stateStore != null) {
+      stateStore.stop();
+      stateStore.close();
+      stateStore = null;
+    }
+  }
+
+  @Before
+  public void setupBase() throws IOException, InterruptedException,
+      InstantiationException, IllegalAccessException {
+    if (stateStore == null) {
+      stateStore = newStateStore(conf);
+      assertNotNull(stateStore);
+    }
+    // Wait for state store to connect
+    stateStore.loadDriver();
+    waitStateStore(stateStore, TimeUnit.SECONDS.toMillis(10));
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/federation/store/TestStateStoreMembershipState.java

@@ -0,0 +1,463 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store;
+
+import static org.apache.hadoop.hdfs.server.federation.FederationTestUtils.NAMENODES;
+import static org.apache.hadoop.hdfs.server.federation.FederationTestUtils.NAMESERVICES;
+import static org.apache.hadoop.hdfs.server.federation.FederationTestUtils.ROUTERS;
+import static org.apache.hadoop.hdfs.server.federation.FederationTestUtils.verifyException;
+import static org.apache.hadoop.hdfs.server.federation.store.FederationStateStoreTestUtils.clearRecords;
+import static org.apache.hadoop.hdfs.server.federation.store.FederationStateStoreTestUtils.createMockRegistrationForNamenode;
+import static org.apache.hadoop.hdfs.server.federation.store.FederationStateStoreTestUtils.synchronizeRecords;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamenodeRegistrationsRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.GetNamenodeRegistrationsResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.NamenodeHeartbeatRequest;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.NamenodeHeartbeatResponse;
+import org.apache.hadoop.hdfs.server.federation.store.protocol.UpdateNamenodeRegistrationRequest;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
+import org.apache.hadoop.util.Time;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+/**
+ * Test the basic {@link MembershipStore} membership functionality.
+ */
+public class TestStateStoreMembershipState extends TestStateStoreBase {
+
+  private static MembershipStore membershipStore;
+
+  @BeforeClass
+  public static void create() {
+    // Reduce expirations to 5 seconds
+    getConf().setLong(
+        DFSConfigKeys.FEDERATION_STORE_MEMBERSHIP_EXPIRATION_MS,
+        TimeUnit.SECONDS.toMillis(5));
+  }
+
+  @Before
+  public void setup() throws IOException, InterruptedException {
+
+    membershipStore =
+        getStateStore().getRegisteredRecordStore(MembershipStore.class);
+
+    // Clear NN registrations
+    assertTrue(clearRecords(getStateStore(), MembershipState.class));
+  }
+
+  @Test
+  public void testNamenodeStateOverride() throws Exception {
+    // Populate the state store
+    // 1) ns0:nn0 - Standby
+    String ns = "ns0";
+    String nn = "nn0";
+    MembershipState report = createRegistration(
+        ns, nn, ROUTERS[1], FederationNamenodeServiceState.STANDBY);
+    assertTrue(namenodeHeartbeat(report));
+
+    // Load data into cache and calculate quorum
+    assertTrue(getStateStore().loadCache(MembershipStore.class, true));
+
+    MembershipState existingState = getNamenodeRegistration(ns, nn);
+    assertEquals(
+        FederationNamenodeServiceState.STANDBY, existingState.getState());
+
+    // Override cache
+    UpdateNamenodeRegistrationRequest request =
+        UpdateNamenodeRegistrationRequest.newInstance(
+            ns, nn, FederationNamenodeServiceState.ACTIVE);
+    assertTrue(membershipStore.updateNamenodeRegistration(request).getResult());
+
+    MembershipState newState = getNamenodeRegistration(ns, nn);
+    assertEquals(FederationNamenodeServiceState.ACTIVE, newState.getState());
+  }
+
+  @Test
+  public void testStateStoreDisconnected() throws Exception {
+
+    // Close the data store driver
+    getStateStore().closeDriver();
+    assertFalse(getStateStore().isDriverReady());
+
+    NamenodeHeartbeatRequest hbRequest = NamenodeHeartbeatRequest.newInstance();
+    hbRequest.setNamenodeMembership(
+        createMockRegistrationForNamenode(
+            "test", "test", FederationNamenodeServiceState.UNAVAILABLE));
+    verifyException(membershipStore, "namenodeHeartbeat",
+        StateStoreUnavailableException.class,
+        new Class[] {NamenodeHeartbeatRequest.class},
+        new Object[] {hbRequest });
+
+    // Information from cache, no exception should be triggered for these
+    // TODO - should cached info expire at some point?
+    GetNamenodeRegistrationsRequest getRequest =
+        GetNamenodeRegistrationsRequest.newInstance();
+    verifyException(membershipStore,
+        "getNamenodeRegistrations", null,
+        new Class[] {GetNamenodeRegistrationsRequest.class},
+        new Object[] {getRequest});
+
+    verifyException(membershipStore,
+        "getExpiredNamenodeRegistrations", null,
+        new Class[] {GetNamenodeRegistrationsRequest.class},
+        new Object[] {getRequest});
+
+    UpdateNamenodeRegistrationRequest overrideRequest =
+        UpdateNamenodeRegistrationRequest.newInstance();
+    verifyException(membershipStore,
+        "updateNamenodeRegistration", null,
+        new Class[] {UpdateNamenodeRegistrationRequest.class},
+        new Object[] {overrideRequest});
+  }
+
+  private void registerAndLoadRegistrations(
+      List<MembershipState> registrationList) throws IOException {
+    // Populate
+    assertTrue(synchronizeRecords(
+        getStateStore(), registrationList, MembershipState.class));
+
+    // Load into cache
+    assertTrue(getStateStore().loadCache(MembershipStore.class, true));
+  }
+
+  private MembershipState createRegistration(String ns, String nn,
+      String router, FederationNamenodeServiceState state) throws IOException {
+    MembershipState record = MembershipState.newInstance(
+        router, ns,
+        nn, "testcluster", "testblock-" + ns, "testrpc-"+ ns + nn,
+        "testservice-"+ ns + nn, "testlifeline-"+ ns + nn,
+        "testweb-" + ns + nn, state, false);
+    return record;
+  }
+
+  @Test
+  public void testRegistrationMajorityQuorum()
+      throws InterruptedException, IOException {
+
+    // Populate the state store with a set of non-matching elements
+    // 1) ns0:nn0 - Standby (newest)
+    // 2) ns0:nn0 - Active (oldest)
+    // 3) ns0:nn0 - Active (2nd oldest)
+    // 4) ns0:nn0 - Active (3nd oldest element, newest active element)
+    // Verify the selected entry is the newest majority opinion (4)
+    String ns = "ns0";
+    String nn = "nn0";
+
+    // Active - oldest
+    MembershipState report = createRegistration(
+        ns, nn, ROUTERS[1], FederationNamenodeServiceState.ACTIVE);
+    assertTrue(namenodeHeartbeat(report));
+    Thread.sleep(1000);
+
+    // Active - 2nd oldest
+    report = createRegistration(
+        ns, nn, ROUTERS[2], FederationNamenodeServiceState.ACTIVE);
+    assertTrue(namenodeHeartbeat(report));
+    Thread.sleep(1000);
+
+    // Active - 3rd oldest, newest active element
+    report = createRegistration(
+        ns, nn, ROUTERS[3], FederationNamenodeServiceState.ACTIVE);
+    assertTrue(namenodeHeartbeat(report));
+
+    // standby - newest overall
+    report = createRegistration(
+        ns, nn, ROUTERS[0], FederationNamenodeServiceState.STANDBY);
+    assertTrue(namenodeHeartbeat(report));
+
+    // Load and calculate quorum
+    assertTrue(getStateStore().loadCache(MembershipStore.class, true));
+
+    // Verify quorum entry
+    MembershipState quorumEntry = getNamenodeRegistration(
+        report.getNameserviceId(), report.getNamenodeId());
+    assertNotNull(quorumEntry);
+    assertEquals(quorumEntry.getRouterId(), ROUTERS[3]);
+  }
+
+  @Test
+  public void testRegistrationQuorumExcludesExpired()
+      throws InterruptedException, IOException {
+
+    // Populate the state store with some expired entries and verify the expired
+    // entries are ignored.
+    // 1) ns0:nn0 - Active
+    // 2) ns0:nn0 - Expired
+    // 3) ns0:nn0 - Expired
+    // 4) ns0:nn0 - Expired
+    // Verify the selected entry is the active entry
+    List<MembershipState> registrationList = new ArrayList<>();
+    String ns = "ns0";
+    String nn = "nn0";
+    String rpcAddress = "testrpcaddress";
+    String serviceAddress = "testserviceaddress";
+    String lifelineAddress = "testlifelineaddress";
+    String blockPoolId = "testblockpool";
+    String clusterId = "testcluster";
+    String webAddress = "testwebaddress";
+    boolean safemode = false;
+
+    // Active
+    MembershipState record = MembershipState.newInstance(
+        ROUTERS[0], ns, nn, clusterId, blockPoolId,
+        rpcAddress, serviceAddress, lifelineAddress, webAddress,
+        FederationNamenodeServiceState.ACTIVE, safemode);
+    registrationList.add(record);
+
+    // Expired
+    record = MembershipState.newInstance(
+        ROUTERS[1], ns, nn, clusterId, blockPoolId,
+        rpcAddress, serviceAddress, lifelineAddress, webAddress,
+        FederationNamenodeServiceState.EXPIRED, safemode);
+    registrationList.add(record);
+
+    // Expired
+    record = MembershipState.newInstance(
+        ROUTERS[2], ns, nn, clusterId, blockPoolId,
+        rpcAddress, serviceAddress, lifelineAddress, webAddress,
+        FederationNamenodeServiceState.EXPIRED, safemode);
+    registrationList.add(record);
+
+    // Expired
+    record = MembershipState.newInstance(
+        ROUTERS[3], ns, nn, clusterId, blockPoolId,
+        rpcAddress, serviceAddress, lifelineAddress, webAddress,
+        FederationNamenodeServiceState.EXPIRED, safemode);
+    registrationList.add(record);
+    registerAndLoadRegistrations(registrationList);
+
+    // Verify quorum entry chooses active membership
+    MembershipState quorumEntry = getNamenodeRegistration(
+        record.getNameserviceId(), record.getNamenodeId());
+    assertNotNull(quorumEntry);
+    assertEquals(ROUTERS[0], quorumEntry.getRouterId());
+  }
+
+  @Test
+  public void testRegistrationQuorumAllExpired() throws IOException {
+
+    // 1) ns0:nn0 - Expired (oldest)
+    // 2) ns0:nn0 - Expired
+    // 3) ns0:nn0 - Expired
+    // 4) ns0:nn0 - Expired
+    // Verify no entry is either selected or cached
+    List<MembershipState> registrationList = new ArrayList<>();
+    String ns = NAMESERVICES[0];
+    String nn = NAMENODES[0];
+    String rpcAddress = "testrpcaddress";
+    String serviceAddress = "testserviceaddress";
+    String lifelineAddress = "testlifelineaddress";
+    String blockPoolId = "testblockpool";
+    String clusterId = "testcluster";
+    String webAddress = "testwebaddress";
+    boolean safemode = false;
+    long startingTime = Time.now();
+
+    // Expired
+    MembershipState record = MembershipState.newInstance(
+        ROUTERS[0], ns, nn, clusterId, blockPoolId,
+        rpcAddress, webAddress, lifelineAddress, webAddress,
+        FederationNamenodeServiceState.EXPIRED, safemode);
+    record.setDateModified(startingTime - 10000);
+    registrationList.add(record);
+
+    // Expired
+    record = MembershipState.newInstance(
+        ROUTERS[1], ns, nn, clusterId, blockPoolId,
+        rpcAddress, serviceAddress, lifelineAddress, webAddress,
+        FederationNamenodeServiceState.EXPIRED, safemode);
+    record.setDateModified(startingTime);
+    registrationList.add(record);
+
+    // Expired
+    record = MembershipState.newInstance(
+        ROUTERS[2], ns, nn, clusterId, blockPoolId,
+        rpcAddress, serviceAddress, lifelineAddress, webAddress,
+        FederationNamenodeServiceState.EXPIRED, safemode);
+    record.setDateModified(startingTime);
+    registrationList.add(record);
+
+    // Expired
+    record = MembershipState.newInstance(
+        ROUTERS[3], ns, nn, clusterId, blockPoolId,
+        rpcAddress, serviceAddress, lifelineAddress, webAddress,
+        FederationNamenodeServiceState.EXPIRED, safemode);
+    record.setDateModified(startingTime);
+    registrationList.add(record);
+
+    registerAndLoadRegistrations(registrationList);
+
+    // Verify no entry is found for this nameservice
+    assertNull(getNamenodeRegistration(
+        record.getNameserviceId(), record.getNamenodeId()));
+  }
+
+  @Test
+  public void testRegistrationNoQuorum()
+      throws InterruptedException, IOException {
+
+    // Populate the state store with a set of non-matching elements
+    // 1) ns0:nn0 - Standby (newest)
+    // 2) ns0:nn0 - Standby (oldest)
+    // 3) ns0:nn0 - Active (2nd oldest)
+    // 4) ns0:nn0 - Active (3nd oldest element, newest active element)
+    // Verify the selected entry is the newest entry (1)
+    MembershipState report1 = createRegistration(
+        NAMESERVICES[0], NAMENODES[0], ROUTERS[1],
+        FederationNamenodeServiceState.STANDBY);
+    assertTrue(namenodeHeartbeat(report1));
+    Thread.sleep(100);
+    MembershipState report2 = createRegistration(
+        NAMESERVICES[0], NAMENODES[0], ROUTERS[2],
+        FederationNamenodeServiceState.ACTIVE);
+    assertTrue(namenodeHeartbeat(report2));
+    Thread.sleep(100);
+    MembershipState report3 = createRegistration(
+        NAMESERVICES[0], NAMENODES[0], ROUTERS[3],
+        FederationNamenodeServiceState.ACTIVE);
+    assertTrue(namenodeHeartbeat(report3));
+    Thread.sleep(100);
+    MembershipState report4 = createRegistration(
+        NAMESERVICES[0], NAMENODES[0], ROUTERS[0],
+        FederationNamenodeServiceState.STANDBY);
+    assertTrue(namenodeHeartbeat(report4));
+
+    // Load and calculate quorum
+    assertTrue(getStateStore().loadCache(MembershipStore.class, true));
+
+    // Verify quorum entry uses the newest data, even though it is standby
+    MembershipState quorumEntry = getNamenodeRegistration(
+        report1.getNameserviceId(), report1.getNamenodeId());
+    assertNotNull(quorumEntry);
+    assertEquals(ROUTERS[0], quorumEntry.getRouterId());
+    assertEquals(
+        FederationNamenodeServiceState.STANDBY, quorumEntry.getState());
+  }
+
+  @Test
+  public void testRegistrationExpired()
+      throws InterruptedException, IOException {
+
+    // Populate the state store with a single NN element
+    // 1) ns0:nn0 - Active
+    // Wait for the entry to expire without heartbeating
+    // Verify the NN entry is populated as EXPIRED internally in the state store
+
+    MembershipState report = createRegistration(
+        NAMESERVICES[0], NAMENODES[0], ROUTERS[0],
+        FederationNamenodeServiceState.ACTIVE);
+    assertTrue(namenodeHeartbeat(report));
+
+    // Load cache
+    assertTrue(getStateStore().loadCache(MembershipStore.class, true));
+
+    // Verify quorum and entry
+    MembershipState quorumEntry = getNamenodeRegistration(
+        report.getNameserviceId(), report.getNamenodeId());
+    assertNotNull(quorumEntry);
+    assertEquals(ROUTERS[0], quorumEntry.getRouterId());
+    assertEquals(FederationNamenodeServiceState.ACTIVE, quorumEntry.getState());
+
+    // Wait past expiration (set in conf to 5 seconds)
+    Thread.sleep(6000);
+    // Reload cache
+    assertTrue(getStateStore().loadCache(MembershipStore.class, true));
+
+    // Verify entry is now expired and is no longer in the cache
+    quorumEntry = getNamenodeRegistration(NAMESERVICES[0], NAMENODES[0]);
+    assertNull(quorumEntry);
+
+    // Verify entry is now expired and can't be used by RPC service
+    quorumEntry = getNamenodeRegistration(
+        report.getNameserviceId(), report.getNamenodeId());
+    assertNull(quorumEntry);
+
+    // Heartbeat again, updates dateModified
+    assertTrue(namenodeHeartbeat(report));
+    // Reload cache
+    assertTrue(getStateStore().loadCache(MembershipStore.class, true));
+
+    // Verify updated entry marked as active and is accessible to RPC server
+    quorumEntry = getNamenodeRegistration(
+        report.getNameserviceId(), report.getNamenodeId());
+    assertNotNull(quorumEntry);
+    assertEquals(ROUTERS[0], quorumEntry.getRouterId());
+    assertEquals(FederationNamenodeServiceState.ACTIVE, quorumEntry.getState());
+  }
+
+  /**
+   * Get a single namenode membership record from the store.
+   *
+   * @param nsId The HDFS nameservice ID to search for
+   * @param nnId The HDFS namenode ID to search for
+   * @return The single NamenodeMembershipRecord that matches the query or null
+   *         if not found.
+   * @throws IOException if the query could not be executed.
+   */
+  private MembershipState getNamenodeRegistration(
+      final String nsId, final String nnId) throws IOException {
+
+    MembershipState partial = MembershipState.newInstance();
+    partial.setNameserviceId(nsId);
+    partial.setNamenodeId(nnId);
+    GetNamenodeRegistrationsRequest request =
+        GetNamenodeRegistrationsRequest.newInstance(partial);
+    GetNamenodeRegistrationsResponse response =
+        membershipStore.getNamenodeRegistrations(request);
+
+    List<MembershipState> results = response.getNamenodeMemberships();
+    if (results != null && results.size() == 1) {
+      MembershipState record = results.get(0);
+      return record;
+    }
+    return null;
+  }
+
+  /**
+   * Register a namenode heartbeat with the state store.
+   *
+   * @param store FederationMembershipStateStore instance to retrieve the
+   *          membership data records.
+   * @param namenode A fully populated namenode membership record to be
+   *          committed to the data store.
+   * @return True if successful, false otherwise.
+   * @throws IOException if the state store query could not be performed.
+   */
+  private boolean namenodeHeartbeat(MembershipState namenode)
+      throws IOException {
+
+    NamenodeHeartbeatRequest request =
+        NamenodeHeartbeatRequest.newInstance(namenode);
+    NamenodeHeartbeatResponse response =
+        membershipStore.namenodeHeartbeat(request);
+    return response.getResult();
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/federation/store/driver/TestStateStoreDriverBase.java

@@ -31,11 +31,14 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Random;
 
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState;
 import org.apache.hadoop.hdfs.server.federation.store.FederationStateStoreTestUtils;
 import org.apache.hadoop.hdfs.server.federation.store.StateStoreService;
 import org.apache.hadoop.hdfs.server.federation.store.records.BaseRecord;
+import org.apache.hadoop.hdfs.server.federation.store.records.MembershipState;
 import org.apache.hadoop.hdfs.server.federation.store.records.Query;
 import org.apache.hadoop.hdfs.server.federation.store.records.QueryResult;
 import org.junit.AfterClass;
@@ -54,6 +57,8 @@ public class TestStateStoreDriverBase {
   private static StateStoreService stateStore;
   private static Configuration conf;
 
+  private static final Random RANDOM = new Random();
+
 
   /**
    * Get the State Store driver.
@@ -78,29 +83,47 @@ public static void tearDownCluster() {
    */
   public static void getStateStore(Configuration config) throws Exception {
     conf = config;
-    stateStore = FederationStateStoreTestUtils.getStateStore(conf);
+    stateStore = FederationStateStoreTestUtils.newStateStore(conf);
   }
 
+  private String generateRandomString() {
+    String randomString = "/randomString-" + RANDOM.nextInt();
+    return randomString;
+  }
+
+  @SuppressWarnings("rawtypes")
+  private <T extends Enum> T generateRandomEnum(Class<T> enumClass) {
+    int x = RANDOM.nextInt(enumClass.getEnumConstants().length);
+    T data = enumClass.getEnumConstants()[x];
+    return data;
+  }
+
+  @SuppressWarnings("unchecked")
   private <T extends BaseRecord> T generateFakeRecord(Class<T> recordClass)
       throws IllegalArgumentException, IllegalAccessException, IOException {
 
-    // TODO add record
+    if (recordClass == MembershipState.class) {
+      return (T) MembershipState.newInstance(generateRandomString(),
+          generateRandomString(), generateRandomString(),
+          generateRandomString(), generateRandomString(),
+          generateRandomString(), generateRandomString(),
+          generateRandomString(), generateRandomString(),
+          generateRandomEnum(FederationNamenodeServiceState.class), false);
+    }
+
     return null;
   }
 
   /**
    * Validate if a record is the same.
    *
-   * @param original
-   * @param committed
+   * @param original Original record.
+   * @param committed Committed record.
    * @param assertEquals Assert if the records are equal or just return.
-   * @return
-   * @throws IllegalArgumentException
-   * @throws IllegalAccessException
+   * @return If the record is successfully validated.
    */
   private boolean validateRecord(
-      BaseRecord original, BaseRecord committed, boolean assertEquals)
-          throws IllegalArgumentException, IllegalAccessException {
+      BaseRecord original, BaseRecord committed, boolean assertEquals) {
 
     boolean ret = true;
 
@@ -131,7 +154,7 @@ private boolean validateRecord(
   }
 
   public static void removeAll(StateStoreDriver driver) throws IOException {
-    // TODO add records to remove
+    driver.removeAll(MembershipState.class);
   }
 
   public <T extends BaseRecord> void testInsert(
@@ -139,17 +162,20 @@ public <T extends BaseRecord> void testInsert(
           throws IllegalArgumentException, IllegalAccessException, IOException {
 
     assertTrue(driver.removeAll(recordClass));
-    QueryResult<T> records = driver.get(recordClass);
-    assertTrue(records.getRecords().isEmpty());
+    QueryResult<T> queryResult0 = driver.get(recordClass);
+    List<T> records0 = queryResult0.getRecords();
+    assertTrue(records0.isEmpty());
 
     // Insert single
     BaseRecord record = generateFakeRecord(recordClass);
     driver.put(record, true, false);
 
     // Verify
-    records = driver.get(recordClass);
-    assertEquals(1, records.getRecords().size());
-    validateRecord(record, records.getRecords().get(0), true);
+    QueryResult<T> queryResult1 = driver.get(recordClass);
+    List<T> records1 = queryResult1.getRecords();
+    assertEquals(1, records1.size());
+    T record0 = records1.get(0);
+    validateRecord(record, record0, true);
 
     // Insert multiple
     List<T> insertList = new ArrayList<>();
@@ -160,8 +186,9 @@ public <T extends BaseRecord> void testInsert(
     driver.putAll(insertList, true, false);
 
     // Verify
-    records = driver.get(recordClass);
-    assertEquals(11, records.getRecords().size());
+    QueryResult<T> queryResult2 = driver.get(recordClass);
+    List<T> records2 = queryResult2.getRecords();
+    assertEquals(11, records2.size());
   }
 
   public <T extends BaseRecord> void testFetchErrors(StateStoreDriver driver,
@@ -319,23 +346,23 @@ public <T extends BaseRecord> void testRemove(
 
   public void testInsert(StateStoreDriver driver)
       throws IllegalArgumentException, IllegalAccessException, IOException {
-    // TODO add records
+    testInsert(driver, MembershipState.class);
   }
 
   public void testPut(StateStoreDriver driver)
       throws IllegalArgumentException, ReflectiveOperationException,
       IOException, SecurityException {
-    // TODO add records
+    testPut(driver, MembershipState.class);
   }
 
   public void testRemove(StateStoreDriver driver)
       throws IllegalArgumentException, IllegalAccessException, IOException {
-    // TODO add records
+    testRemove(driver, MembershipState.class);
   }
 
   public void testFetchErrors(StateStoreDriver driver)
       throws IllegalArgumentException, IllegalAccessException, IOException {
-    // TODO add records
+    testFetchErrors(driver, MembershipState.class);
   }
 
   /**

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/federation/store/records/TestMembershipState.java

@@ -0,0 +1,129 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hdfs.server.federation.store.records;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.IOException;
+
+import org.apache.hadoop.hdfs.server.federation.resolver.FederationNamenodeServiceState;
+import org.apache.hadoop.hdfs.server.federation.store.driver.StateStoreSerializer;
+import org.junit.Test;
+
+/**
+ * Test the Membership State records.
+ */
+public class TestMembershipState {
+
+  private static final String ROUTER = "router";
+  private static final String NAMESERVICE = "nameservice";
+  private static final String NAMENODE = "namenode";
+  private static final String CLUSTER_ID = "cluster";
+  private static final String BLOCKPOOL_ID = "blockpool";
+  private static final String RPC_ADDRESS = "rpcaddress";
+  private static final String SERVICE_ADDRESS = "serviceaddress";
+  private static final String LIFELINE_ADDRESS = "lifelineaddress";
+  private static final String WEB_ADDRESS = "webaddress";
+  private static final boolean SAFE_MODE = false;
+
+  private static final long DATE_CREATED = 100;
+  private static final long DATE_MODIFIED = 200;
+
+  private static final long NUM_BLOCKS = 300;
+  private static final long NUM_FILES = 400;
+  private static final int NUM_DEAD = 500;
+  private static final int NUM_ACTIVE = 600;
+  private static final int NUM_DECOM = 700;
+  private static final int NUM_DECOM_ACTIVE = 800;
+  private static final int NUM_DECOM_DEAD = 900;
+  private static final long NUM_BLOCK_MISSING = 1000;
+
+  private static final long TOTAL_SPACE = 1100;
+  private static final long AVAILABLE_SPACE = 1200;
+
+  private static final FederationNamenodeServiceState STATE =
+      FederationNamenodeServiceState.ACTIVE;
+
+  private MembershipState createRecord() throws IOException {
+
+    MembershipState record = MembershipState.newInstance(
+        ROUTER, NAMESERVICE, NAMENODE, CLUSTER_ID,
+        BLOCKPOOL_ID, RPC_ADDRESS, SERVICE_ADDRESS, LIFELINE_ADDRESS,
+        WEB_ADDRESS, STATE, SAFE_MODE);
+    record.setDateCreated(DATE_CREATED);
+    record.setDateModified(DATE_MODIFIED);
+
+    MembershipStats stats = MembershipStats.newInstance();
+    stats.setNumOfBlocks(NUM_BLOCKS);
+    stats.setNumOfFiles(NUM_FILES);
+    stats.setNumOfActiveDatanodes(NUM_ACTIVE);
+    stats.setNumOfDeadDatanodes(NUM_DEAD);
+    stats.setNumOfDecommissioningDatanodes(NUM_DECOM);
+    stats.setNumOfDecomActiveDatanodes(NUM_DECOM_ACTIVE);
+    stats.setNumOfDecomDeadDatanodes(NUM_DECOM_DEAD);
+    stats.setNumOfBlocksMissing(NUM_BLOCK_MISSING);
+    stats.setTotalSpace(TOTAL_SPACE);
+    stats.setAvailableSpace(AVAILABLE_SPACE);
+    record.setStats(stats);
+    return record;
+  }
+
+  private void validateRecord(MembershipState record) throws IOException {
+
+    assertEquals(ROUTER, record.getRouterId());
+    assertEquals(NAMESERVICE, record.getNameserviceId());
+    assertEquals(CLUSTER_ID, record.getClusterId());
+    assertEquals(BLOCKPOOL_ID, record.getBlockPoolId());
+    assertEquals(RPC_ADDRESS, record.getRpcAddress());
+    assertEquals(WEB_ADDRESS, record.getWebAddress());
+    assertEquals(STATE, record.getState());
+    assertEquals(SAFE_MODE, record.getIsSafeMode());
+    assertEquals(DATE_CREATED, record.getDateCreated());
+    assertEquals(DATE_MODIFIED, record.getDateModified());
+
+    MembershipStats stats = record.getStats();
+    assertEquals(NUM_BLOCKS, stats.getNumOfBlocks());
+    assertEquals(NUM_FILES, stats.getNumOfFiles());
+    assertEquals(NUM_ACTIVE, stats.getNumOfActiveDatanodes());
+    assertEquals(NUM_DEAD, stats.getNumOfDeadDatanodes());
+    assertEquals(NUM_DECOM, stats.getNumOfDecommissioningDatanodes());
+    assertEquals(NUM_DECOM_ACTIVE, stats.getNumOfDecomActiveDatanodes());
+    assertEquals(NUM_DECOM_DEAD, stats.getNumOfDecomDeadDatanodes());
+    assertEquals(TOTAL_SPACE, stats.getTotalSpace());
+    assertEquals(AVAILABLE_SPACE, stats.getAvailableSpace());
+  }
+
+  @Test
+  public void testGetterSetter() throws IOException {
+    MembershipState record = createRecord();
+    validateRecord(record);
+  }
+
+  @Test
+  public void testSerialization() throws IOException {
+
+    MembershipState record = createRecord();
+
+    StateStoreSerializer serializer = StateStoreSerializer.getSerializer();
+    String serializedString = serializer.serializeString(record);
+    MembershipState newRecord =
+        serializer.deserialize(serializedString, MembershipState.class);
+
+    validateRecord(newRecord);
+  }
+}