HDFS-16540. Data locality is lost when DataNode pod restarts in kubernetes (#4170)

This reverts the previous commit 4e47eb66d1
undone so I could reapply with the '.' after the HDFS-16540 as is done
in all other commits.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeManager.java

@@ -1171,6 +1171,7 @@ public void registerDatanode(DatanodeRegistration nodeReg)
         nodeN = null;
       }
   
+      boolean updateHost2DatanodeMap = false;
       if (nodeS != null) {
         if (nodeN == nodeS) {
           // The same datanode has been just restarted to serve the same data 
@@ -1189,7 +1190,11 @@ public void registerDatanode(DatanodeRegistration nodeReg)
             nodes with its data cleared (or user can just remove the StorageID
             value in "VERSION" file under the data directory of the datanode,
             but this is might not work if VERSION file format has changed 
-         */        
+         */
+          // Check if nodeS's host information is same as nodeReg's, if not,
+          // it needs to update host2DatanodeMap accordringly.
+          updateHost2DatanodeMap = !nodeS.getXferAddr().equals(nodeReg.getXferAddr());
+
           NameNode.stateChangeLog.info("BLOCK* registerDatanode: " + nodeS
               + " is replaced by " + nodeReg + " with the same storageID "
               + nodeReg.getDatanodeUuid());
@@ -1199,6 +1204,11 @@ nodes with its data cleared (or user can just remove the StorageID
         try {
           // update cluster map
           getNetworkTopology().remove(nodeS);
+
+          // Update Host2DatanodeMap
+          if (updateHost2DatanodeMap) {
+            getHost2DatanodeMap().remove(nodeS);
+          }
           if(shouldCountVersion(nodeS)) {
             decrementVersionCount(nodeS.getSoftwareVersion());
           }
@@ -1217,6 +1227,11 @@ nodes with its data cleared (or user can just remove the StorageID
             nodeS.setDependentHostNames(
                 getNetworkDependenciesWithDefault(nodeS));
           }
+
+          if (updateHost2DatanodeMap) {
+            getHost2DatanodeMap().add(nodeS);
+          }
+
           getNetworkTopology().add(nodeS);
           resolveUpgradeDomain(nodeS);
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestDatanodeManager.java

@@ -138,6 +138,35 @@ public void testNumVersionsCorrectAfterReregister()
         mapToCheck.get("version1").intValue(), 1);
   }
 
+  /**
+   * This test checks that if a node is re-registered with a different ip, its
+   * host2DatanodeMap is correctly updated with the new ip.
+   */
+  @Test
+  public void testHost2NodeMapCorrectAfterReregister()
+          throws IOException, InterruptedException {
+    //Create the DatanodeManager which will be tested
+    FSNamesystem fsn = Mockito.mock(FSNamesystem.class);
+    Mockito.when(fsn.hasWriteLock()).thenReturn(true);
+    Configuration conf = new Configuration();
+    DatanodeManager dm = mockDatanodeManager(fsn, conf);
+
+    String storageID = "someStorageID1";
+    String ipOld = "someIPOld" + storageID;
+    String ipNew = "someIPNew" + storageID;
+
+    dm.registerDatanode(new DatanodeRegistration(
+            new DatanodeID(ipOld, "", storageID, 9000, 0, 0, 0),
+            null, null, "version"));
+
+    dm.registerDatanode(new DatanodeRegistration(
+            new DatanodeID(ipNew, "", storageID, 9000, 0, 0, 0),
+            null, null, "version"));
+
+    assertNull("should be no node with old ip", dm.getDatanodeByHost(ipOld));
+    assertNotNull("should be a node with new ip", dm.getDatanodeByHost(ipNew));
+  }
+
   /**
    * This test sends a random sequence of node registrations and node removals
    * to the DatanodeManager (of nodes with different IDs and versions), and