YARN-8333. Load balance YARN services using RegistryDNS multiple A records. Contributed by Eric Yang

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-registry/src/main/java/org/apache/hadoop/registry/server/dns/BaseServiceRecordProcessor.java

@@ -290,6 +290,26 @@ protected Name getContainerName()
           domain));
     }
 
+    /**
+     * Return the DNS name constructed from the component name.
+     *
+     * @return the DNS naem.
+     * @throws PathNotFoundException
+     * @throws TextParseException
+     */
+    protected Name getComponentName()
+        throws PathNotFoundException, TextParseException {
+      String service = RegistryPathUtils.lastPathEntry(
+          RegistryPathUtils.parentOf(RegistryPathUtils.parentOf(getPath())));
+      String component = getRecord().get("yarn:component").toLowerCase();
+      String user = RegistryPathUtils.getUsername(getPath());
+      return Name.fromString(MessageFormat.format("{0}.{1}.{2}.{3}",
+          component,
+          service,
+          user,
+          domain));
+    }
+
   }
 
   /**

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-registry/src/main/java/org/apache/hadoop/registry/server/dns/ContainerServiceRecordProcessor.java

@@ -242,7 +242,8 @@ public AContainerRecordDescriptor(String path,
       }
       try {
         this.setTarget(InetAddress.getByName(ip));
-        this.setNames(new Name[] {getContainerName(), getContainerIDName()});
+        this.setNames(new Name[] {getContainerName(), getContainerIDName(),
+            getComponentName()});
       } catch (Exception e) {
         throw new IllegalStateException(e);
       }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-registry/src/test/java/org/apache/hadoop/registry/server/dns/TestRegistryDNS.java

@@ -115,32 +115,47 @@ public class TestRegistryDNS extends Assert {
       + "}\n";
   static final String CONTAINER_RECORD = "{\n"
       + "  \"type\" : \"JSONServiceRecord\",\n"
-      + "  \"description\" : \"COMP-NAME\",\n"
+      + "  \"description\" : \"httpd-1\",\n"
       + "  \"external\" : [ ],\n"
       + "  \"internal\" : [ ],\n"
       + "  \"yarn:id\" : \"container_e50_1451931954322_0016_01_000002\",\n"
       + "  \"yarn:persistence\" : \"container\",\n"
       + "  \"yarn:ip\" : \"172.17.0.19\",\n"
-      + "  \"yarn:hostname\" : \"0a134d6329ba\"\n"
+      + "  \"yarn:hostname\" : \"host1\",\n"
+      + "  \"yarn:component\" : \"httpd\"\n"
+      + "}\n";
+
+  static final String CONTAINER_RECORD2 = "{\n"
+      + "  \"type\" : \"JSONServiceRecord\",\n"
+      + "  \"description\" : \"httpd-2\",\n"
+      + "  \"external\" : [ ],\n"
+      + "  \"internal\" : [ ],\n"
+      + "  \"yarn:id\" : \"container_e50_1451931954322_0016_01_000003\",\n"
+      + "  \"yarn:persistence\" : \"container\",\n"
+      + "  \"yarn:ip\" : \"172.17.0.20\",\n"
+      + "  \"yarn:hostname\" : \"host2\",\n"
+      + "  \"yarn:component\" : \"httpd\"\n"
       + "}\n";
 
   private static final String CONTAINER_RECORD_NO_IP = "{\n"
       + "  \"type\" : \"JSONServiceRecord\",\n"
-      + "  \"description\" : \"COMP-NAME\",\n"
+      + "  \"description\" : \"httpd-1\",\n"
       + "  \"external\" : [ ],\n"
       + "  \"internal\" : [ ],\n"
       + "  \"yarn:id\" : \"container_e50_1451931954322_0016_01_000002\",\n"
-      + "  \"yarn:persistence\" : \"container\"\n"
+      + "  \"yarn:persistence\" : \"container\",\n"
+      + "  \"yarn:component\" : \"httpd\"\n"
       + "}\n";
 
   private static final String CONTAINER_RECORD_YARN_PERSISTANCE_ABSENT = "{\n"
       + "  \"type\" : \"JSONServiceRecord\",\n"
-      + "  \"description\" : \"COMP-NAME\",\n"
+      + "  \"description\" : \"httpd-1\",\n"
       + "  \"external\" : [ ],\n"
       + "  \"internal\" : [ ],\n"
       + "  \"yarn:id\" : \"container_e50_1451931954322_0016_01_000003\",\n"
       + "  \"yarn:ip\" : \"172.17.0.19\",\n"
-      + "  \"yarn:hostname\" : \"0a134d6329bb\"\n"
+      + "  \"yarn:hostname\" : \"0a134d6329bb\",\n"
+      + "  \"yarn:component\" : \"httpd\""
       + "}\n";
 
   @Before
@@ -229,7 +244,7 @@ public void testContainerRegistration() throws Exception {
     assertEquals("wrong result", "172.17.0.19",
         ((ARecord) recs[0]).getAddress().getHostAddress());
 
-    recs = assertDNSQuery("comp-name.test1.root.dev.test.", 1);
+    recs = assertDNSQuery("httpd-1.test1.root.dev.test.", 1);
     assertTrue("not an ARecord", recs[0] instanceof ARecord);
   }
 
@@ -268,7 +283,7 @@ public void testRecordTTL() throws Exception {
         ((ARecord) recs[0]).getAddress().getHostAddress());
     assertEquals("wrong ttl", 30L, recs[0].getTTL());
 
-    recs = assertDNSQuery("comp-name.test1.root.dev.test.", 1);
+    recs = assertDNSQuery("httpd-1.test1.root.dev.test.", 1);
     assertTrue("not an ARecord", recs[0] instanceof ARecord);
 
     assertEquals("wrong ttl", 30L, recs[0].getTTL());
@@ -286,7 +301,7 @@ public void testReverseLookup() throws Exception {
     // start assessing whether correct records are available
     Record[] recs = assertDNSQuery("19.0.17.172.in-addr.arpa.", Type.PTR, 1);
     assertEquals("wrong result",
-        "comp-name.test1.root.dev.test.",
+        "httpd-1.test1.root.dev.test.",
         ((PTRRecord) recs[0]).getTarget().toString());
   }
 
@@ -312,7 +327,7 @@ public void testReverseLookupInLargeNetwork() throws Exception {
     // start assessing whether correct records are available
     Record[] recs = assertDNSQuery("19.0.17.172.in-addr.arpa.", Type.PTR, 1);
     assertEquals("wrong result",
-        "comp-name.test1.root.dev.test.",
+        "httpd-1.test1.root.dev.test.",
         ((PTRRecord) recs[0]).getTarget().toString());
   }
 
@@ -490,7 +505,7 @@ public void testAAAALookup() throws Exception {
     assertEquals("wrong result", "172.17.0.19",
         ((AAAARecord) recs[0]).getAddress().getHostAddress());
 
-    recs = assertDNSQuery("comp-name.test1.root.dev.test.", Type.AAAA, 1);
+    recs = assertDNSQuery("httpd-1.test1.root.dev.test.", Type.AAAA, 1);
     assertTrue("not an ARecord", recs[0] instanceof AAAARecord);
   }
 
@@ -565,13 +580,13 @@ public void testReadMasterFile() throws Exception {
     assertEquals("wrong result", "172.17.0.19",
         ((ARecord) recs[0]).getAddress().getHostAddress());
 
-    recs = assertDNSQuery("comp-name.test1.root.dev.test.", 1);
+    recs = assertDNSQuery("httpd-1.test1.root.dev.test.", 1);
     assertTrue("not an ARecord", recs[0] instanceof ARecord);
 
     // lookup dyanmic reverse records
     recs = assertDNSQuery("19.0.17.172.in-addr.arpa.", Type.PTR, 1);
     assertEquals("wrong result",
-        "comp-name.test1.root.dev.test.",
+        "httpd-1.test1.root.dev.test.",
         ((PTRRecord) recs[0]).getTarget().toString());
 
     // now lookup static reverse records
@@ -649,6 +664,27 @@ public void testExternalCNAMERecord() throws Exception {
         assertDNSQueryNotNull("mail.yahoo.com.", Type.CNAME);
   }
 
+  @Test
+  public void testMultiARecord() throws Exception {
+    ServiceRecord record = getMarshal().fromBytes("somepath",
+        CONTAINER_RECORD.getBytes());
+    ServiceRecord record2 = getMarshal().fromBytes("somepath",
+        CONTAINER_RECORD2.getBytes());
+    getRegistryDNS().register(
+        "/registry/users/root/services/org-apache-slider/test1/components/"
+            + "ctr-e50-1451931954322-0016-01-000002",
+        record);
+    getRegistryDNS().register(
+        "/registry/users/root/services/org-apache-slider/test1/components/"
+            + "ctr-e50-1451931954322-0016-01-000003",
+        record2);
+
+    // start assessing whether correct records are available
+    Record[] recs =
+        assertDNSQuery("httpd.test1.root.dev.test.", 2);
+    assertTrue("not an ARecord", recs[0] instanceof ARecord);
+    assertTrue("not an ARecord", recs[1] instanceof ARecord);
+  }
   public RegistryDNS getRegistryDNS() {
     return registryDNS;
   }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/markdown/yarn-service/ServiceDiscovery.md

@@ -65,6 +65,18 @@ Note that YARN service framework assigns `COMPONENT_INSTANCE_NAME` for each cont
 assigned `0` since it is the first and only instance for the `hbasemaster` component. In case of `regionserver` component, it can have multiple containers
  and so be named as such: `regionserver-0`, `regionserver-1`, `regionserver-2` ... etc
 
+Each YARN service component also has Multi-A Records for container fault tolerance or load balancing via RegistryDNS.  The naming format is defined as:
+```
+${COMPONENT_NAME}.${SERVICE_NAME}.${USER}.${DOMAIN}
+```
+
+For example, a component named www for application app launched by Chuck with 3 containers will have DNS records that look like:
+```
+www.app.chuck.example.com IN A 123.123.123.1
+www.app.chuck.example.com IN A 123.123.123.1
+www.app.chuck.example.com IN A 123.123.123.1
+```
+
 `Disclaimer`: The DNS implementation is still experimental. It should not be used as a fully-functional DNS.