HDFS-14017. [SBN read] ObserverReadProxyProviderWithIPFailover should work with HA configuration. Contributed by Chen Liang.

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/client/HdfsClientConfigKeys.java

@@ -192,6 +192,9 @@ public interface HdfsClientConfigKeys {
   String DFS_PROVIDED_ALIASMAP_INMEMORY_RPC_ADDRESS =
       "dfs.provided.aliasmap.inmemory.dnrpc-address";
 
+  String DFS_CLIENT_FAILOVER_IPFAILOVER_VIRTUAL_ADDRESS =
+      Failover.PREFIX + "ipfailover.virtual-address";
+
   /**
    * These are deprecated config keys to client code.
    */

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/server/namenode/ha/ObserverReadProxyProviderWithIPFailover.java

@@ -17,24 +17,99 @@
  */
 package org.apache.hadoop.hdfs.server.namenode.ha;
 
-import java.io.IOException;
 import java.net.URI;
 
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hdfs.protocol.ClientProtocol;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static org.apache.hadoop.hdfs.client.HdfsClientConfigKeys.DFS_CLIENT_FAILOVER_IPFAILOVER_VIRTUAL_ADDRESS;
 
 /**
- * ObserverReadProxyProvider with IPFailoverProxyProvider
- * as the failover method.
+ * Extends {@link ObserverReadProxyProvider} to support NameNode IP failover.
+ *
+ * For Observer reads a client needs to know physical addresses of all
+ * NameNodes, so that it could switch between active and observer nodes
+ * for write and read requests.
+ *
+ * Traditional {@link IPFailoverProxyProvider} works with a virtual
+ * address of the NameNode. If active NameNode fails the virtual address
+ * is assigned to the standby NameNode, and IPFailoverProxyProvider, which
+ * keeps talking to the same virtual address is in fact now connects to
+ * the new physical server.
+ *
+ * To combine these behaviors ObserverReadProxyProviderWithIPFailover
+ * should both
+ * <ol>
+ * <li> Maintain all physical addresses of NameNodes in order to allow
+ * observer reads, and
+ * <li> Should rely on the virtual address of the NameNode in order to
+ * perform failover by assuming that the virtual address always points
+ * to the active NameNode.
+ * </ol>
+ *
+ * An example of a configuration to leverage
+ * ObserverReadProxyProviderWithIPFailover
+ * should include the following values:
+ * <pre>{@code
+ * fs.defaultFS = hdfs://mycluster
+ * dfs.nameservices = mycluster
+ * dfs.ha.namenodes.mycluster = ha1,ha2
+ * dfs.namenode.rpc-address.mycluster.ha1 = nn01-ha1.com:8020
+ * dfs.namenode.rpc-address.mycluster.ha2 = nn01-ha2.com:8020
+ * dfs.client.failover.ipfailover.virtual-address.mycluster = nn01.com:8020
+ * dfs.client.failover.proxy.provider.mycluster =
+ *     org.apache...ObserverReadProxyProviderWithIPFailover
+ * }</pre>
+ * Here {@code nn01.com:8020} is the virtual address of the active NameNode,
+ * while {@code nn01-ha1.com:8020} and {@code nn01-ha2.com:8020}
+ * are the physically addresses the two NameNodes.
+ *
+ * With this configuration, client will use
+ * ObserverReadProxyProviderWithIPFailover, which creates proxies for both
+ * nn01-ha1 and nn01-ha2, used for read/write RPC calls, but for the failover,
+ * it relies on the virtual address nn01.com
  */
-public class
-ObserverReadProxyProviderWithIPFailover<T extends ClientProtocol>
-extends ObserverReadProxyProvider<T> {
 
+public class ObserverReadProxyProviderWithIPFailover<T extends ClientProtocol>
+    extends ObserverReadProxyProvider<T> {
+  private static final Logger LOG = LoggerFactory.getLogger(
+      ObserverReadProxyProviderWithIPFailover.class);
+
+  /**
+   * By default ObserverReadProxyProviderWithIPFailover
+   * uses {@link IPFailoverProxyProvider} for failover.
+   */
   public ObserverReadProxyProviderWithIPFailover(
-      Configuration conf, URI uri, Class<T> xface,
-      HAProxyFactory<T> factory) throws IOException {
-    super(conf, uri, xface, factory,
-        new IPFailoverProxyProvider<T>(conf, uri, xface,factory));
+      Configuration conf, URI uri, Class<T> xface, HAProxyFactory<T> factory) {
+    this(conf, uri, xface, factory,
+        new IPFailoverProxyProvider<>(conf,
+            getFailoverVirtualIP(conf, uri.getHost()), xface, factory));
+  }
+
+  @Override
+  public boolean useLogicalURI() {
+    return true;
+  }
+
+  public ObserverReadProxyProviderWithIPFailover(
+      Configuration conf, URI uri, Class<T> xface, HAProxyFactory<T> factory,
+      AbstractNNFailoverProxyProvider<T> failoverProxy) {
+    super(conf, uri, xface, factory, failoverProxy);
+  }
+
+  private static URI getFailoverVirtualIP(
+      Configuration conf, String nameServiceID) {
+    String configKey = DFS_CLIENT_FAILOVER_IPFAILOVER_VIRTUAL_ADDRESS
+        + "." + nameServiceID;
+    String virtualIP = conf.get(configKey);
+    LOG.info("Name service ID {} will use virtual IP {} for failover",
+        nameServiceID, virtualIP);
+    if (virtualIP == null) {
+      throw new IllegalArgumentException("Virtual IP for failover not found,"
+          + "misconfigured " + configKey + "?");
+    }
+    return URI.create(virtualIP);
   }
-}
+}