HDFS-4269. Datanode rejects all datanode registrations from localhost in single-node developer setup on Windows. Contributed by Chris Nauroth.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1420492 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -269,6 +269,9 @@ Trunk (Unreleased)
     HDFS-4260 Fix HDFS tests to set test dir to a valid HDFS path as opposed
     to the local build path (Chri Nauroth via Sanjay)
 
+    HDFS-4269. Datanode rejects all datanode registrations from localhost
+    in single-node developer setup on Windows. (Chris Nauroth via suresh)
+
 Release 2.0.3-alpha - Unreleased 
 
   INCOMPATIBLE CHANGES

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

@@ -633,7 +633,9 @@ public class DatanodeManager {
       // Mostly called inside an RPC, update ip and peer hostname
       String hostname = dnAddress.getHostName();
       String ip = dnAddress.getHostAddress();
-      if (hostname.equals(ip)) {
+      if (!isNameResolved(dnAddress)) {
+        // Reject registration of unresolved datanode to prevent performance
+        // impact of repetitive DNS lookups later.
         LOG.warn("Unresolved datanode registration from " + ip);
         throw new DisallowedDatanodeException(nodeReg);
       }
@@ -1061,6 +1063,22 @@ public class DatanodeManager {
     }
     return names;
   }
+
+  /**
+   * Checks if name resolution was successful for the given address.  If IP
+   * address and host name are the same, then it means name resolution has
+   * failed.  As a special case, the loopback address is also considered
+   * acceptable.  This is particularly important on Windows, where 127.0.0.1 does
+   * not resolve to "localhost".
+   * 
+   * @param address InetAddress to check
+   * @return boolean true if name resolution successful or address is loopback
+   */
+  private static boolean isNameResolved(InetAddress address) {
+    String hostname = address.getHostName();
+    String ip = address.getHostAddress();
+    return !hostname.equals(ip) || address.isLoopbackAddress();
+  }
   
   private void setDatanodeDead(DatanodeDescriptor node) {
     node.setLastUpdate(0);