HDFS-3150. Add option for clients to contact DNs via hostname. Contributed by Eli Collins

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1373143 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -26,6 +26,8 @@ Release 2.0.1-alpha - UNRELEASED
 
     HDFS-3637. Add support for encrypting the DataTransferProtocol. (atm)
 
+    HDFS-3150. Add option for clients to contact DNs via hostname. (eli)
+
   IMPROVEMENTS
 
     HDFS-3390. DFSAdmin should print full stack traces of errors when DEBUG

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

@@ -86,11 +86,11 @@ protected boolean removeEldestEntry(
     }
 
     private synchronized ClientDatanodeProtocol getDatanodeProxy(
-        DatanodeInfo node, Configuration conf, int socketTimeout)
+        DatanodeInfo node, Configuration conf, int socketTimeout,
-        throws IOException {
+        boolean connectToDnViaHostname) throws IOException {
       if (proxy == null) {
         proxy = DFSUtil.createClientDatanodeProtocolProxy(node, conf,
-            socketTimeout);
+            socketTimeout, connectToDnViaHostname);
       }
       return proxy;
     }
@@ -156,14 +156,16 @@ private void removeBlockLocalPathInfo(ExtendedBlock b) {
    */
   static BlockReaderLocal newBlockReader(Configuration conf, String file,
       ExtendedBlock blk, Token<BlockTokenIdentifier> token, DatanodeInfo node,
-      int socketTimeout, long startOffset, long length) throws IOException {
+      int socketTimeout, long startOffset, long length,
+      boolean connectToDnViaHostname) throws IOException {
 
     LocalDatanodeInfo localDatanodeInfo = getLocalDatanodeInfo(node
         .getIpcPort());
     // check the cache first
     BlockLocalPathInfo pathinfo = localDatanodeInfo.getBlockLocalPathInfo(blk);
     if (pathinfo == null) {
-      pathinfo = getBlockPathInfo(blk, node, conf, socketTimeout, token);
+      pathinfo = getBlockPathInfo(blk, node, conf, socketTimeout, token,
+          connectToDnViaHostname);
     }
 
     // check to see if the file exists. It may so happen that the
@@ -241,11 +243,12 @@ private static synchronized LocalDatanodeInfo getLocalDatanodeInfo(int port) {
   
   private static BlockLocalPathInfo getBlockPathInfo(ExtendedBlock blk,
       DatanodeInfo node, Configuration conf, int timeout,
-      Token<BlockTokenIdentifier> token) throws IOException {
+      Token<BlockTokenIdentifier> token, boolean connectToDnViaHostname)
+          throws IOException {
     LocalDatanodeInfo localDatanodeInfo = getLocalDatanodeInfo(node.getIpcPort());
     BlockLocalPathInfo pathinfo = null;
     ClientDatanodeProtocol proxy = localDatanodeInfo.getDatanodeProxy(node,
-        conf, timeout);
+        conf, timeout, connectToDnViaHostname);
     try {
       // make RPC to local datanode to find local pathnames of blocks
       pathinfo = proxy.getBlockLocalPathInfo(blk, token);

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

@@ -49,6 +49,8 @@
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_ENCRYPT_DATA_TRANSFER_KEY;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_REPLICATION_DEFAULT;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_REPLICATION_KEY;
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_CLIENT_USE_DN_HOSTNAME;
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_CLIENT_USE_DN_HOSTNAME_DEFAULT;
 
 import java.io.BufferedOutputStream;
 import java.io.DataInputStream;
@@ -216,6 +218,7 @@ static class Conf {
     final String taskId;
     final FsPermission uMask;
     final boolean useLegacyBlockReader;
+    final boolean connectToDnViaHostname;
 
     Conf(Configuration conf) {
       maxFailoverAttempts = conf.getInt(
@@ -266,6 +269,8 @@ static class Conf {
       useLegacyBlockReader = conf.getBoolean(
           DFS_CLIENT_USE_LEGACY_BLOCKREADER,
           DFS_CLIENT_USE_LEGACY_BLOCKREADER_DEFAULT);
+      connectToDnViaHostname = conf.getBoolean(DFS_CLIENT_USE_DN_HOSTNAME,
+          DFS_CLIENT_USE_DN_HOSTNAME_DEFAULT);
     }
 
     private int getChecksumType(Configuration conf) {
@@ -476,6 +481,14 @@ String getClientName() {
     return clientName;
   }
 
+  /**
+   * @return whether the client should use hostnames instead of IPs
+   *    when connecting to DataNodes
+   */
+  boolean connectToDnViaHostname() {
+    return dfsClientConf.connectToDnViaHostname;
+  }
+
   void checkOpen() throws IOException {
     if (!clientRunning) {
       IOException result = new IOException("Filesystem closed");
@@ -732,12 +745,12 @@ public long renewDelegationToken(Token<DelegationTokenIdentifier> token)
    */
   static BlockReader getLocalBlockReader(Configuration conf,
       String src, ExtendedBlock blk, Token<BlockTokenIdentifier> accessToken,
-      DatanodeInfo chosenNode, int socketTimeout, long offsetIntoBlock)
+      DatanodeInfo chosenNode, int socketTimeout, long offsetIntoBlock,
-      throws InvalidToken, IOException {
+      boolean connectToDnViaHostname) throws InvalidToken, IOException {
     try {
       return BlockReaderLocal.newBlockReader(conf, src, blk, accessToken,
           chosenNode, socketTimeout, offsetIntoBlock, blk.getNumBytes()
-              - offsetIntoBlock);
+              - offsetIntoBlock, connectToDnViaHostname);
     } catch (RemoteException re) {
       throw re.unwrapRemoteException(InvalidToken.class,
           AccessControlException.class);
@@ -1464,7 +1477,8 @@ public HdfsFileStatus getFileLinkInfo(String src) throws IOException {
   public MD5MD5CRC32FileChecksum getFileChecksum(String src) throws IOException {
     checkOpen();
     return getFileChecksum(src, namenode, socketFactory,
-        dfsClientConf.socketTimeout, getDataEncryptionKey());
+        dfsClientConf.socketTimeout, getDataEncryptionKey(),
+        dfsClientConf.connectToDnViaHostname);
   }
   
   @InterfaceAudience.Private
@@ -1510,7 +1524,8 @@ public DataEncryptionKey getDataEncryptionKey()
    */
   public static MD5MD5CRC32FileChecksum getFileChecksum(String src,
       ClientProtocol namenode, SocketFactory socketFactory, int socketTimeout,
-      DataEncryptionKey encryptionKey) throws IOException {
+      DataEncryptionKey encryptionKey, boolean connectToDnViaHostname)
+      throws IOException {
     //get all block locations
     LocatedBlocks blockLocations = callGetBlockLocations(namenode, src, 0, Long.MAX_VALUE);
     if (null == blockLocations) {
@@ -1548,9 +1563,11 @@ public static MD5MD5CRC32FileChecksum getFileChecksum(String src,
         try {
           //connect to a datanode
           sock = socketFactory.createSocket();
-          NetUtils.connect(sock,
+          String dnAddr = datanodes[j].getXferAddr(connectToDnViaHostname);
-              NetUtils.createSocketAddr(datanodes[j].getXferAddr()),
+          if (LOG.isDebugEnabled()) {
-              timeout);
+            LOG.debug("Connecting to datanode " + dnAddr);
+          }
+          NetUtils.connect(sock, NetUtils.createSocketAddr(dnAddr), timeout);
           sock.setSoTimeout(timeout);
 
           OutputStream unbufOut = NetUtils.getOutputStream(sock);

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

@@ -52,6 +52,8 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final String  DFS_CLIENT_WRITE_REPLACE_DATANODE_ON_FAILURE_POLICY_DEFAULT = "DEFAULT";
   public static final String  DFS_CLIENT_SOCKET_CACHE_CAPACITY_KEY = "dfs.client.socketcache.capacity";
   public static final int     DFS_CLIENT_SOCKET_CACHE_CAPACITY_DEFAULT = 16;
+  public static final String  DFS_CLIENT_USE_DN_HOSTNAME = "dfs.client.use.datanode.hostname";
+  public static final boolean DFS_CLIENT_USE_DN_HOSTNAME_DEFAULT = false;
 
   // HA related configuration
   public static final String  DFS_CLIENT_FAILOVER_PROXY_PROVIDER_KEY_PREFIX = "dfs.client.failover.proxy.provider";
@@ -81,6 +83,8 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final boolean DFS_DATANODE_SYNC_BEHIND_WRITES_DEFAULT = false;
   public static final String  DFS_DATANODE_DROP_CACHE_BEHIND_READS_KEY = "dfs.datanode.drop.cache.behind.reads";
   public static final boolean DFS_DATANODE_DROP_CACHE_BEHIND_READS_DEFAULT = false;
+  public static final String  DFS_DATANODE_USE_DN_HOSTNAME = "dfs.datanode.use.datanode.hostname";
+  public static final boolean DFS_DATANODE_USE_DN_HOSTNAME_DEFAULT = false;
 
   public static final String  DFS_NAMENODE_HTTP_PORT_KEY = "dfs.http.port";
   public static final int     DFS_NAMENODE_HTTP_PORT_DEFAULT = 50070;

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

@@ -199,7 +199,8 @@ private long readBlockLength(LocatedBlock locatedblock) throws IOException {
       
       try {
         cdp = DFSUtil.createClientDatanodeProtocolProxy(
-        datanode, dfsClient.conf, dfsClient.getConf().socketTimeout, locatedblock);
+            datanode, dfsClient.conf, dfsClient.getConf().socketTimeout,
+            dfsClient.getConf().connectToDnViaHostname, locatedblock);
         
         final long n = cdp.getReplicaVisibleLength(locatedblock.getBlock());
         
@@ -716,8 +717,12 @@ private DNAddrPair chooseDataNode(LocatedBlock block)
       DatanodeInfo[] nodes = block.getLocations();
       try {
         DatanodeInfo chosenNode = bestNode(nodes, deadNodes);
-        InetSocketAddress targetAddr = 
+        final String dnAddr =
-          NetUtils.createSocketAddr(chosenNode.getXferAddr());
+            chosenNode.getXferAddr(dfsClient.connectToDnViaHostname());
+        if (DFSClient.LOG.isDebugEnabled()) {
+          DFSClient.LOG.debug("Connecting to datanode " + dnAddr);
+        }
+        InetSocketAddress targetAddr = NetUtils.createSocketAddr(dnAddr);
         return new DNAddrPair(chosenNode, targetAddr);
       } catch (IOException ie) {
         String blockInfo = block.getBlock() + " file=" + src;
@@ -875,7 +880,8 @@ protected BlockReader getBlockReader(InetSocketAddress dnAddr,
     
     if (dfsClient.shouldTryShortCircuitRead(dnAddr)) {
       return DFSClient.getLocalBlockReader(dfsClient.conf, src, block,
-          blockToken, chosenNode, dfsClient.hdfsTimeout, startOffset);
+          blockToken, chosenNode, dfsClient.hdfsTimeout, startOffset,
+          dfsClient.connectToDnViaHostname());
     }
     
     IOException err = null;
@@ -1183,7 +1189,7 @@ static DatanodeInfo bestNode(DatanodeInfo nodes[],
     throw new IOException("No live nodes contain current block");
   }
 
-  /** Utility class to encapsulate data node info and its ip address. */
+  /** Utility class to encapsulate data node info and its address. */
   static class DNAddrPair {
     DatanodeInfo info;
     InetSocketAddress addr;

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

@@ -1100,7 +1100,7 @@ private boolean createBlockOutputStream(DatanodeInfo[] nodes, long newGS,
           if (ie instanceof InvalidEncryptionKeyException && refetchEncryptionKey > 0) {
             DFSClient.LOG.info("Will fetch a new encryption key and retry, " 
                 + "encryption key was invalid when connecting to "
-                + nodes[0].getXferAddr() + " : " + ie);
+                + nodes[0] + " : " + ie);
             // The encryption key used is invalid.
             refetchEncryptionKey--;
             dfsClient.clearDataEncryptionKey();
@@ -1112,7 +1112,8 @@ private boolean createBlockOutputStream(DatanodeInfo[] nodes, long newGS,
           // find the datanode that matches
           if (firstBadLink.length() != 0) {
             for (int i = 0; i < nodes.length; i++) {
-              if (nodes[i].getXferAddr().equals(firstBadLink)) {
+              // NB: Unconditionally using the xfer addr w/o hostname
+              if (firstBadLink.equals(nodes[i].getXferAddr())) {
                 errorIndex = i;
                 break;
               }
@@ -1216,11 +1217,11 @@ private void setLastException(IOException e) {
    */
   static Socket createSocketForPipeline(final DatanodeInfo first,
       final int length, final DFSClient client) throws IOException {
-    if(DFSClient.LOG.isDebugEnabled()) {
+    final String dnAddr = first.getXferAddr(client.connectToDnViaHostname());
-      DFSClient.LOG.debug("Connecting to datanode " + first);
+    if (DFSClient.LOG.isDebugEnabled()) {
+      DFSClient.LOG.debug("Connecting to datanode " + dnAddr);
     }
-    final InetSocketAddress isa =
+    final InetSocketAddress isa = NetUtils.createSocketAddr(dnAddr);
-      NetUtils.createSocketAddr(first.getXferAddr());
     final Socket sock = client.socketFactory.createSocket();
     final int timeout = client.getDatanodeReadTimeout(length);
     NetUtils.connect(sock, isa, client.getRandomLocalInterfaceAddr(), timeout);

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

@@ -847,17 +847,17 @@ public static int roundBytesToGB(long bytes) {
   /** Create a {@link ClientDatanodeProtocol} proxy */
   public static ClientDatanodeProtocol createClientDatanodeProtocolProxy(
       DatanodeID datanodeid, Configuration conf, int socketTimeout,
-      LocatedBlock locatedBlock) throws IOException {
+      boolean connectToDnViaHostname, LocatedBlock locatedBlock) throws IOException {
     return new ClientDatanodeProtocolTranslatorPB(datanodeid, conf, socketTimeout,
-             locatedBlock);
+        connectToDnViaHostname, locatedBlock);
   }
   
   /** Create {@link ClientDatanodeProtocol} proxy using kerberos ticket */
   static ClientDatanodeProtocol createClientDatanodeProtocolProxy(
-      DatanodeID datanodeid, Configuration conf, int socketTimeout)
+      DatanodeID datanodeid, Configuration conf, int socketTimeout,
-      throws IOException {
+      boolean connectToDnViaHostname) throws IOException {
     return new ClientDatanodeProtocolTranslatorPB(
-        datanodeid, conf, socketTimeout);
+        datanodeid, conf, socketTimeout, connectToDnViaHostname);
   }
   
   /** Create a {@link ClientDatanodeProtocol} proxy */

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/DatanodeID.java

@@ -104,7 +104,7 @@ public String getXferAddr() {
   /**
    * @return IP:ipcPort string
    */
-  public String getIpcAddr() {
+  private String getIpcAddr() {
     return ipAddr + ":" + ipcPort;
   }
 
@@ -122,6 +122,29 @@ public String getXferAddrWithHostname() {
     return hostName + ":" + xferPort;
   }
 
+  /**
+   * @return hostname:ipcPort
+   */
+  private String getIpcAddrWithHostname() {
+    return hostName + ":" + ipcPort;
+  }
+
+  /**
+   * @param useHostname true to use the DN hostname, use the IP otherwise
+   * @return name:xferPort
+   */
+  public String getXferAddr(boolean useHostname) {
+    return useHostname ? getXferAddrWithHostname() : getXferAddr();
+  }
+
+  /**
+   * @param useHostname true to use the DN hostname, use the IP otherwise
+   * @return name:ipcPort
+   */
+  public String getIpcAddr(boolean useHostname) {
+    return useHostname ? getIpcAddrWithHostname() : getIpcAddr();
+  }
+
   /**
    * @return data storage ID.
    */

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientDatanodeProtocolTranslatorPB.java

@@ -73,10 +73,10 @@ public class ClientDatanodeProtocolTranslatorPB implements
       RefreshNamenodesRequestProto.newBuilder().build();
 
   public ClientDatanodeProtocolTranslatorPB(DatanodeID datanodeid,
-      Configuration conf, int socketTimeout, LocatedBlock locatedBlock)
+      Configuration conf, int socketTimeout, boolean connectToDnViaHostname,
-      throws IOException {
+      LocatedBlock locatedBlock) throws IOException {
     rpcProxy = createClientDatanodeProtocolProxy( datanodeid, conf, 
-                  socketTimeout, locatedBlock);
+                  socketTimeout, connectToDnViaHostname, locatedBlock);
   }
   
   public ClientDatanodeProtocolTranslatorPB(InetSocketAddress addr,
@@ -90,11 +90,17 @@ public ClientDatanodeProtocolTranslatorPB(InetSocketAddress addr,
    * @param datanodeid Datanode to connect to.
    * @param conf Configuration.
    * @param socketTimeout Socket timeout to use.
+   * @param connectToDnViaHostname connect to the Datanode using its hostname
    * @throws IOException
    */
   public ClientDatanodeProtocolTranslatorPB(DatanodeID datanodeid,
-      Configuration conf, int socketTimeout) throws IOException {
+      Configuration conf, int socketTimeout, boolean connectToDnViaHostname)
-    InetSocketAddress addr = NetUtils.createSocketAddr(datanodeid.getIpcAddr());
+      throws IOException {
+    final String dnAddr = datanodeid.getIpcAddr(connectToDnViaHostname);
+    InetSocketAddress addr = NetUtils.createSocketAddr(dnAddr);
+    if (LOG.isDebugEnabled()) {
+      LOG.debug("Connecting to datanode " + dnAddr + " addr=" + addr);
+    }
     rpcProxy = createClientDatanodeProtocolProxy(addr,
         UserGroupInformation.getCurrentUser(), conf,
         NetUtils.getDefaultSocketFactory(conf), socketTimeout);
@@ -102,10 +108,11 @@ public ClientDatanodeProtocolTranslatorPB(DatanodeID datanodeid,
 
   static ClientDatanodeProtocolPB createClientDatanodeProtocolProxy(
       DatanodeID datanodeid, Configuration conf, int socketTimeout,
-      LocatedBlock locatedBlock) throws IOException {
+      boolean connectToDnViaHostname, LocatedBlock locatedBlock) throws IOException {
-    InetSocketAddress addr = NetUtils.createSocketAddr(datanodeid.getIpcAddr());
+    final String dnAddr = datanodeid.getIpcAddr(connectToDnViaHostname);
+    InetSocketAddress addr = NetUtils.createSocketAddr(dnAddr);
     if (LOG.isDebugEnabled()) {
-      LOG.debug("ClientDatanodeProtocol addr=" + addr);
+      LOG.debug("Connecting to datanode " + dnAddr + " addr=" + addr);
     }
     
     // Since we're creating a new UserGroupInformation here, we know that no

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DNConf.java

@@ -55,7 +55,7 @@ class DNConf {
   final boolean dropCacheBehindReads;
   final boolean syncOnClose;
   final boolean encryptDataTransfer;
-  
+  final boolean connectToDnViaHostname;
 
   final long readaheadLength;
   final long heartBeatInterval;
@@ -97,7 +97,9 @@ public DNConf(Configuration conf) {
     dropCacheBehindReads = conf.getBoolean(
         DFSConfigKeys.DFS_DATANODE_DROP_CACHE_BEHIND_READS_KEY,
         DFSConfigKeys.DFS_DATANODE_DROP_CACHE_BEHIND_READS_DEFAULT);
-    
+    connectToDnViaHostname = conf.getBoolean(
+        DFSConfigKeys.DFS_DATANODE_USE_DN_HOSTNAME,
+        DFSConfigKeys.DFS_DATANODE_USE_DN_HOSTNAME_DEFAULT);
     this.blockReportInterval = conf.getLong(DFS_BLOCKREPORT_INTERVAL_MSEC_KEY,
     DFS_BLOCKREPORT_INTERVAL_MSEC_DEFAULT);
     

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java

@@ -279,6 +279,7 @@ public static InetSocketAddress createSocketAddr(String target) {
   private Configuration conf;
 
   private final String userWithLocalPathAccess;
+  private boolean connectToDnViaHostname;
   ReadaheadPool readaheadPool;
 
   /**
@@ -299,8 +300,11 @@ public static InetSocketAddress createSocketAddr(String target) {
            final SecureResources resources) throws IOException {
     super(conf);
 
-    this.userWithLocalPathAccess = conf
+    this.userWithLocalPathAccess =
-        .get(DFSConfigKeys.DFS_BLOCK_LOCAL_PATH_ACCESS_USER_KEY);
+        conf.get(DFSConfigKeys.DFS_BLOCK_LOCAL_PATH_ACCESS_USER_KEY);
+    this.connectToDnViaHostname = conf.getBoolean(
+        DFSConfigKeys.DFS_DATANODE_USE_DN_HOSTNAME,
+        DFSConfigKeys.DFS_DATANODE_USE_DN_HOSTNAME_DEFAULT);
     try {
       hostName = getHostName(conf);
       LOG.info("Configured hostname is " + hostName);
@@ -882,7 +886,7 @@ public String getDisplayName() {
   /**
    * NB: The datanode can perform data transfer on the streaming
    * address however clients are given the IPC IP address for data
-   * transfer, and that may be be a different address.
+   * transfer, and that may be a different address.
    * 
    * @return socket address for data transfer
    */
@@ -929,12 +933,12 @@ DatanodeProtocolClientSideTranslatorPB connectToNN(
   }
 
   public static InterDatanodeProtocol createInterDataNodeProtocolProxy(
-      DatanodeID datanodeid, final Configuration conf, final int socketTimeout)
+      DatanodeID datanodeid, final Configuration conf, final int socketTimeout,
-    throws IOException {
+      final boolean connectToDnViaHostname) throws IOException {
-    final InetSocketAddress addr =
+    final String dnAddr = datanodeid.getIpcAddr(connectToDnViaHostname);
-      NetUtils.createSocketAddr(datanodeid.getIpcAddr());
+    final InetSocketAddress addr = NetUtils.createSocketAddr(dnAddr);
-    if (InterDatanodeProtocol.LOG.isDebugEnabled()) {
+    if (LOG.isDebugEnabled()) {
-      InterDatanodeProtocol.LOG.debug("InterDatanodeProtocol addr=" + addr);
+      LOG.debug("Connecting to datanode " + dnAddr + " addr=" + addr);
     }
     final UserGroupInformation loginUgi = UserGroupInformation.getLoginUser();
     try {
@@ -1390,8 +1394,11 @@ public void run() {
       final boolean isClient = clientname.length() > 0;
       
       try {
-        InetSocketAddress curTarget = 
+        final String dnAddr = targets[0].getXferAddr(connectToDnViaHostname);
-          NetUtils.createSocketAddr(targets[0].getXferAddr());
+        InetSocketAddress curTarget = NetUtils.createSocketAddr(dnAddr);
+        if (LOG.isDebugEnabled()) {
+          LOG.debug("Connecting to datanode " + dnAddr);
+        }
         sock = newSocket();
         NetUtils.connect(sock, curTarget, dnConf.socketTimeout);
         sock.setSoTimeout(targets.length * dnConf.socketTimeout);
@@ -1847,7 +1854,7 @@ private void recoverBlock(RecoveringBlock rBlock) throws IOException {
         DatanodeRegistration bpReg = bpos.bpRegistration;
         InterDatanodeProtocol datanode = bpReg.equals(id)?
             this: DataNode.createInterDataNodeProtocolProxy(id, getConf(),
-                dnConf.socketTimeout);
+                dnConf.socketTimeout, dnConf.connectToDnViaHostname);
         ReplicaRecoveryInfo info = callInitReplicaRecovery(datanode, rBlock);
         if (info != null &&
             info.getGenerationStamp() >= block.getGenerationStamp() &&

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataXceiver.java

@@ -86,7 +86,7 @@ class DataXceiver extends Receiver implements Runnable {
   private final DataNode datanode;
   private final DNConf dnConf;
   private final DataXceiverServer dataXceiverServer;
-
+  private final boolean connectToDnViaHostname;
   private long opStartTime; //the start time of receiving an Op
   private final SocketInputWrapper socketIn;
   private OutputStream socketOut;
@@ -113,6 +113,7 @@ private DataXceiver(Socket s,
     this.isLocal = s.getInetAddress().equals(s.getLocalAddress());
     this.datanode = datanode;
     this.dataXceiverServer = dataXceiverServer;
+    this.connectToDnViaHostname = datanode.getDnConf().connectToDnViaHostname;
     remoteAddress = s.getRemoteSocketAddress().toString();
     localAddress = s.getLocalSocketAddress().toString();
 
@@ -404,7 +405,10 @@ public void writeBlock(final ExtendedBlock block,
       if (targets.length > 0) {
         InetSocketAddress mirrorTarget = null;
         // Connect to backup machine
-        mirrorNode = targets[0].getXferAddr();
+        mirrorNode = targets[0].getXferAddr(connectToDnViaHostname);
+        if (LOG.isDebugEnabled()) {
+          LOG.debug("Connecting to datanode " + mirrorNode);
+        }
         mirrorTarget = NetUtils.createSocketAddr(mirrorNode);
         mirrorSock = datanode.newSocket();
         try {
@@ -457,7 +461,8 @@ public void writeBlock(final ExtendedBlock block,
           if (isClient) {
             BlockOpResponseProto.newBuilder()
               .setStatus(ERROR)
-              .setFirstBadLink(mirrorNode)
+               // NB: Unconditionally using the xfer addr w/o hostname
+              .setFirstBadLink(targets[0].getXferAddr())
               .build()
               .writeDelimitedTo(replyOut);
             replyOut.flush();
@@ -729,8 +734,11 @@ public void replaceBlock(final ExtendedBlock block,
     
     try {
       // get the output stream to the proxy
-      InetSocketAddress proxyAddr =
+      final String dnAddr = proxySource.getXferAddr(connectToDnViaHostname);
-        NetUtils.createSocketAddr(proxySource.getXferAddr());
+      if (LOG.isDebugEnabled()) {
+        LOG.debug("Connecting to datanode " + dnAddr);
+      }
+      InetSocketAddress proxyAddr = NetUtils.createSocketAddr(dnAddr);
       proxySock = datanode.newSocket();
       NetUtils.connect(proxySock, proxyAddr, dnConf.socketTimeout);
       proxySock.setSoTimeout(dnConf.socketTimeout);
@@ -891,6 +899,7 @@ private void checkAccess(DataOutputStream out, final boolean reply,
             if (mode == BlockTokenSecretManager.AccessMode.WRITE) {
               DatanodeRegistration dnR = 
                 datanode.getDNRegistrationForBP(blk.getBlockPoolId());
+              // NB: Unconditionally using the xfer addr w/o hostname
               resp.setFirstBadLink(dnR.getXferAddr());
             }
             resp.build().writeDelimitedTo(out);

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FileChecksumServlets.java

@@ -127,7 +127,7 @@ public void doGet(HttpServletRequest request, HttpServletResponse response
             datanode, conf, getUGI(request, conf));
         final ClientProtocol nnproxy = dfs.getNamenode();
         final MD5MD5CRC32FileChecksum checksum = DFSClient.getFileChecksum(
-            path, nnproxy, socketFactory, socketTimeout, dfs.getDataEncryptionKey());
+            path, nnproxy, socketFactory, socketTimeout, dfs.getDataEncryptionKey(), false);
         MD5MD5CRC32FileChecksum.write(xml, checksum);
       } catch(IOException ioe) {
         writeXml(ioe, path, xml);

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

@@ -53,7 +53,7 @@
   <name>dfs.datanode.address</name>
   <value>0.0.0.0:50010</value>
   <description>
-    The address where the datanode server will listen to.
+    The datanode server address and port for data transfer.
     If the port is 0 then the server will start on a free port.
   </description>
 </property>
@@ -920,6 +920,22 @@
   </description>
 </property>
 
+<property>
+  <name>dfs.client.use.datanode.hostname</name>
+  <value>false</value>
+  <description>Whether clients should use datanode hostnames when
+    connecting to datanodes.
+  </description>
+</property>
+
+<property>
+  <name>dfs.datanode.use.datanode.hostname</name>
+  <value>false</value>
+  <description>Whether datanodes should use datanode hostnames when
+    connecting to other datanodes for data transfer.
+  </description>
+</property>
+
 <property>
   <name>dfs.client.local.interfaces</name>
   <value></value>

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSCluster.java

@@ -144,6 +144,7 @@ public static class Builder {
     private boolean setupHostsFile = false;
     private MiniDFSNNTopology nnTopology = null;
     private boolean checkExitOnShutdown = true;
+    private boolean checkDataNodeHostConfig = false;
     
     public Builder(Configuration conf) {
       this.conf = conf;
@@ -253,6 +254,14 @@ public Builder checkExitOnShutdown(boolean val) {
       return this;
     }
 
+    /**
+     * Default: false
+     */
+    public Builder checkDataNodeHostConfig(boolean val) {
+      this.checkDataNodeHostConfig = val;
+      return this;
+    }
+    
     /**
      * Default: null
      */
@@ -316,7 +325,8 @@ private MiniDFSCluster(Builder builder) throws IOException {
                        builder.waitSafeMode,
                        builder.setupHostsFile,
                        builder.nnTopology,
-                       builder.checkExitOnShutdown);
+                       builder.checkExitOnShutdown,
+                       builder.checkDataNodeHostConfig);
   }
   
   public class DataNodeProperties {
@@ -550,7 +560,7 @@ public MiniDFSCluster(int nameNodePort,
     initMiniDFSCluster(conf, numDataNodes, format,
         manageNameDfsDirs, true, manageDataDfsDirs, operation, racks, hosts,
         simulatedCapacities, null, true, false,
-        MiniDFSNNTopology.simpleSingleNN(nameNodePort, 0), true);
+        MiniDFSNNTopology.simpleSingleNN(nameNodePort, 0), true, false);
   }
 
   private void initMiniDFSCluster(
@@ -560,7 +570,8 @@ private void initMiniDFSCluster(
       StartupOption operation, String[] racks,
       String[] hosts, long[] simulatedCapacities, String clusterId,
       boolean waitSafeMode, boolean setupHostsFile,
-      MiniDFSNNTopology nnTopology, boolean checkExitOnShutdown)
+      MiniDFSNNTopology nnTopology, boolean checkExitOnShutdown,
+      boolean checkDataNodeHostConfig)
   throws IOException {
     ExitUtil.disableSystemExit();
 
@@ -616,7 +627,7 @@ private void initMiniDFSCluster(
 
     // Start the DataNodes
     startDataNodes(conf, numDataNodes, manageDataDfsDirs, operation, racks,
-        hosts, simulatedCapacities, setupHostsFile);
+        hosts, simulatedCapacities, setupHostsFile, false, checkDataNodeHostConfig);
     waitClusterUp();
     //make sure ProxyUsers uses the latest conf
     ProxyUsers.refreshSuperUserGroupsConfiguration(conf);
@@ -957,7 +968,21 @@ public synchronized void startDataNodes(Configuration conf, int numDataNodes,
                              long[] simulatedCapacities,
                              boolean setupHostsFile) throws IOException {
     startDataNodes(conf, numDataNodes, manageDfsDirs, operation, racks, hosts,
-                   simulatedCapacities, setupHostsFile, false);
+        simulatedCapacities, setupHostsFile, false, false);
+  }
+
+  /**
+   * @see MiniDFSCluster#startDataNodes(Configuration, int, boolean, StartupOption,
+   * String[], String[], long[], boolean, boolean, boolean)
+   */
+  public synchronized void startDataNodes(Configuration conf, int numDataNodes,
+      boolean manageDfsDirs, StartupOption operation, 
+      String[] racks, String[] hosts,
+      long[] simulatedCapacities,
+      boolean setupHostsFile,
+      boolean checkDataNodeAddrConfig) throws IOException {
+    startDataNodes(conf, numDataNodes, manageDfsDirs, operation, racks, hosts,
+        simulatedCapacities, setupHostsFile, checkDataNodeAddrConfig, false);
   }
 
   /**
@@ -983,19 +1008,25 @@ public synchronized void startDataNodes(Configuration conf, int numDataNodes,
    * @param simulatedCapacities array of capacities of the simulated data nodes
    * @param setupHostsFile add new nodes to dfs hosts files
    * @param checkDataNodeAddrConfig if true, only set DataNode port addresses if not already set in config
+   * @param checkDataNodeHostConfig if true, only set DataNode hostname key if not already set in config
    *
    * @throws IllegalStateException if NameNode has been shutdown
    */
   public synchronized void startDataNodes(Configuration conf, int numDataNodes,
-                             boolean manageDfsDirs, StartupOption operation, 
+      boolean manageDfsDirs, StartupOption operation, 
-                             String[] racks, String[] hosts,
+      String[] racks, String[] hosts,
-                             long[] simulatedCapacities,
+      long[] simulatedCapacities,
-                             boolean setupHostsFile,
+      boolean setupHostsFile,
-                             boolean checkDataNodeAddrConfig) throws IOException {
+      boolean checkDataNodeAddrConfig,
+      boolean checkDataNodeHostConfig) throws IOException {
     if (operation == StartupOption.RECOVER) {
       return;
     }
-    conf.set(DFS_DATANODE_HOST_NAME_KEY, "127.0.0.1");
+    if (checkDataNodeHostConfig) {
+      conf.setIfUnset(DFS_DATANODE_HOST_NAME_KEY, "127.0.0.1");
+    } else {
+      conf.set(DFS_DATANODE_HOST_NAME_KEY, "127.0.0.1");
+    }
 
     int curDatanodesNum = dataNodes.size();
     // for mincluster's the default initialDelay for BRs is 0

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestDFSClientRetries.java

@@ -763,7 +763,7 @@ public void testClientDNProtocolTimeout() throws IOException {
 
     try {
       proxy = DFSUtil.createClientDatanodeProtocolProxy(
-          fakeDnId, conf, 500, fakeBlock);
+          fakeDnId, conf, 500, false, fakeBlock);
 
       proxy.getReplicaVisibleLength(new ExtendedBlock("bpid", 1));
       fail ("Did not get expected exception: SocketTimeoutException");

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestDistributedFileSystem.java

@@ -417,7 +417,6 @@ public void testFileChecksum() throws Exception {
 
     final Configuration conf = getTestConfiguration();
     conf.setBoolean(DFSConfigKeys.DFS_WEBHDFS_ENABLED_KEY, true);
-    conf.set(DFSConfigKeys.DFS_DATANODE_HOST_NAME_KEY, "localhost");
 
     final MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).numDataNodes(2).build();
     final FileSystem hdfs = cluster.getFileSystem();

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestFileCreation.java

@@ -171,7 +171,14 @@ public void testServerDefaults() throws IOException {
 
   @Test
   public void testFileCreation() throws IOException {
-    checkFileCreation(null);
+    checkFileCreation(null, false);
+  }
+
+  /** Same test but the client should use DN hostnames */
+  @Test
+  public void testFileCreationUsingHostname() throws IOException {
+    assumeTrue(System.getProperty("os.name").startsWith("Linux"));
+    checkFileCreation(null, true);
   }
 
   /** Same test but the client should bind to a local interface */
@@ -180,10 +187,10 @@ public void testFileCreationSetLocalInterface() throws IOException {
     assumeTrue(System.getProperty("os.name").startsWith("Linux"));
 
     // The mini cluster listens on the loopback so we can use it here
-    checkFileCreation("lo");
+    checkFileCreation("lo", false);
 
     try {
-      checkFileCreation("bogus-interface");
+      checkFileCreation("bogus-interface", false);
       fail("Able to specify a bogus interface");
     } catch (UnknownHostException e) {
       assertEquals("No such interface bogus-interface", e.getMessage());
@@ -193,16 +200,28 @@ public void testFileCreationSetLocalInterface() throws IOException {
   /**
    * Test if file creation and disk space consumption works right
    * @param netIf the local interface, if any, clients should use to access DNs
+   * @param useDnHostname whether the client should contact DNs by hostname
    */
-  public void checkFileCreation(String netIf) throws IOException {
+  public void checkFileCreation(String netIf, boolean useDnHostname)
+      throws IOException {
     Configuration conf = new HdfsConfiguration();
     if (netIf != null) {
       conf.set(DFSConfigKeys.DFS_CLIENT_LOCAL_INTERFACES, netIf);
     }
+    conf.setBoolean(DFSConfigKeys.DFS_CLIENT_USE_DN_HOSTNAME, useDnHostname);
+    if (useDnHostname) {
+      // Since the mini cluster only listens on the loopback we have to
+      // ensure the hostname used to access DNs maps to the loopback. We
+      // do this by telling the DN to advertise localhost as its hostname
+      // instead of the default hostname.
+      conf.set(DFSConfigKeys.DFS_DATANODE_HOST_NAME_KEY, "localhost");
+    }
     if (simulatedStorage) {
       SimulatedFSDataset.setFactory(conf);
     }
-    MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf).build();
+    MiniDFSCluster cluster = new MiniDFSCluster.Builder(conf)
+      .checkDataNodeHostConfig(true)
+      .build();
     FileSystem fs = cluster.getFileSystem();
     try {
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestHftpFileSystem.java

@@ -92,7 +92,6 @@ public static void setUp() throws IOException {
     RAN.setSeed(seed);
 
     config = new Configuration();
-    config.set(DFSConfigKeys.DFS_DATANODE_HOST_NAME_KEY, "localhost");
     cluster = new MiniDFSCluster.Builder(config).numDataNodes(2).build();
     hdfs = cluster.getFileSystem();
     blockPoolId = cluster.getNamesystem().getBlockPoolId();

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestMiniDFSCluster.java

@@ -20,6 +20,7 @@
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assume.assumeTrue;
 
 import java.io.File;
 
@@ -41,6 +42,7 @@ public class TestMiniDFSCluster {
   private static final String CLUSTER_2 = "cluster2";
   private static final String CLUSTER_3 = "cluster3";
   private static final String CLUSTER_4 = "cluster4";
+  private static final String CLUSTER_5 = "cluster5";
   protected String testDataPath;
   protected File testDataDir;
   @Before
@@ -125,4 +127,25 @@ public void testIsClusterUpAfterShutdown() throws Throwable {
       }  
     }
   }
+
+  /** MiniDFSCluster should not clobber dfs.datanode.hostname if requested */
+  @Test(timeout=100000)
+  public void testClusterSetDatanodeHostname() throws Throwable {
+    assumeTrue(System.getProperty("os.name").startsWith("Linux"));
+    Configuration conf = new HdfsConfiguration();
+    conf.set(DFSConfigKeys.DFS_DATANODE_HOST_NAME_KEY, "MYHOST");
+    File testDataCluster5 = new File(testDataPath, CLUSTER_5);
+    String c5Path = testDataCluster5.getAbsolutePath();
+    conf.set(MiniDFSCluster.HDFS_MINIDFS_BASEDIR, c5Path);
+    MiniDFSCluster cluster5 = new MiniDFSCluster.Builder(conf)
+      .numDataNodes(1)
+      .checkDataNodeHostConfig(true)
+      .build();
+    try {
+      Assert.assertEquals("DataNode hostname config not respected", "MYHOST",
+          cluster5.getDataNodes().get(0).getDatanodeId().getHostName());
+    } finally {
+      MiniDFSCluster.shutdownCluster(cluster5);
+    }
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestShortCircuitLocalRead.java

@@ -246,7 +246,7 @@ public void testGetBlockLocalPathInfo() throws IOException, InterruptedException
             @Override
             public ClientDatanodeProtocol run() throws Exception {
               return DFSUtil.createClientDatanodeProtocolProxy(dnInfo, conf,
-                  60000);
+                  60000, false);
             }
           });
       
@@ -264,7 +264,7 @@ public ClientDatanodeProtocol run() throws Exception {
             @Override
             public ClientDatanodeProtocol run() throws Exception {
               return DFSUtil.createClientDatanodeProtocolProxy(dnInfo, conf,
-                  60000);
+                  60000, false);
             }
           });
       try {

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/security/token/block/TestBlockToken.java

@@ -304,7 +304,7 @@ public void testBlockTokenRpcLeak() throws Exception {
       long endTime = Time.now() + 3000;
       while (Time.now() < endTime) {
         proxy = DFSUtil.createClientDatanodeProtocolProxy(fakeDnId, conf, 1000,
-            fakeBlock);
+            false, fakeBlock);
         assertEquals(block3.getBlockId(), proxy.getReplicaVisibleLength(block3));
         if (proxy != null) {
           RPC.stopProxy(proxy);

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/DataNodeTestUtils.java

@@ -105,10 +105,13 @@ public static DatanodeProtocolClientSideTranslatorPB spyOnBposToNN(
   }
 
   public static InterDatanodeProtocol createInterDatanodeProtocolProxy(
-      DataNode dn, DatanodeID datanodeid, final Configuration conf
+      DataNode dn, DatanodeID datanodeid, final Configuration conf,
-      ) throws IOException {
+      boolean connectToDnViaHostname) throws IOException {
+    if (connectToDnViaHostname != dn.getDnConf().connectToDnViaHostname) {
+      throw new AssertionError("Unexpected DN hostname configuration");
+    }
     return DataNode.createInterDataNodeProtocolProxy(datanodeid, conf,
-        dn.getDnConf().socketTimeout);
+        dn.getDnConf().socketTimeout, dn.getDnConf().connectToDnViaHostname);
   }
   
   public static void shutdownBlockScanner(DataNode dn) {

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/TestInterDatanodeProtocol.java

@@ -29,6 +29,7 @@
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.hdfs.DFSClientAdapter;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
 import org.apache.hadoop.hdfs.DFSTestUtil;
 import org.apache.hadoop.hdfs.DistributedFileSystem;
 import org.apache.hadoop.hdfs.HdfsConfiguration;
@@ -59,6 +60,8 @@
 import org.junit.Assert;
 import org.junit.Test;
 
+import static org.junit.Assume.assumeTrue;
+
 /**
  * This tests InterDataNodeProtocol for block handling. 
  */
@@ -125,17 +128,42 @@ public static LocatedBlock getLastLocatedBlock(
     return blocks.get(blocks.size() - 1);
   }
 
+  /** Test block MD access via a DN */
+  @Test
+  public void testBlockMetaDataInfo() throws Exception {
+    checkBlockMetaDataInfo(false);
+  }
+
+  /** The same as above, but use hostnames for DN<->DN communication */
+  @Test
+  public void testBlockMetaDataInfoWithHostname() throws Exception {
+    assumeTrue(System.getProperty("os.name").startsWith("Linux"));
+    checkBlockMetaDataInfo(true);
+  }
+
   /**
    * The following test first creates a file.
    * It verifies the block information from a datanode.
-   * Then, it updates the block with new information and verifies again. 
+   * Then, it updates the block with new information and verifies again.
+   * @param useDnHostname whether DNs should connect to other DNs by hostname
    */
-  @Test
+  private void checkBlockMetaDataInfo(boolean useDnHostname) throws Exception {
-  public void testBlockMetaDataInfo() throws Exception {
     MiniDFSCluster cluster = null;
 
+    conf.setBoolean(DFSConfigKeys.DFS_DATANODE_USE_DN_HOSTNAME, useDnHostname);
+    if (useDnHostname) {
+      // Since the mini cluster only listens on the loopback we have to
+      // ensure the hostname used to access DNs maps to the loopback. We
+      // do this by telling the DN to advertise localhost as its hostname
+      // instead of the default hostname.
+      conf.set(DFSConfigKeys.DFS_DATANODE_HOST_NAME_KEY, "localhost");
+    }
+
     try {
-      cluster = new MiniDFSCluster.Builder(conf).numDataNodes(3).build();
+      cluster = new MiniDFSCluster.Builder(conf)
+        .numDataNodes(3)
+        .checkDataNodeHostConfig(true)
+        .build();
       cluster.waitActive();
 
       //create a file
@@ -154,7 +182,7 @@ public void testBlockMetaDataInfo() throws Exception {
       //connect to a data node
       DataNode datanode = cluster.getDataNode(datanodeinfo[0].getIpcPort());
       InterDatanodeProtocol idp = DataNodeTestUtils.createInterDatanodeProtocolProxy(
-          datanode, datanodeinfo[0], conf);
+          datanode, datanodeinfo[0], conf, useDnHostname);
       
       //stop block scanner, so we could compare lastScanTime
       DataNodeTestUtils.shutdownBlockScanner(datanode);
@@ -364,7 +392,7 @@ public void testInterDNProtocolTimeout() throws Throwable {
 
     try {
       proxy = DataNode.createInterDataNodeProtocolProxy(
-          dInfo, conf, 500);
+          dInfo, conf, 500, false);
       proxy.initReplicaRecovery(new RecoveringBlock(
           new ExtendedBlock("bpid", 1), null, 100));
       fail ("Expected SocketTimeoutException exception, but did not get.");