HDFS-6731. Merging change r1612715 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1612718 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -102,6 +102,9 @@ Release 2.6.0 - UNRELEASED
     HDFS-6704. Fix the command to launch JournalNode in HDFS-HA document.
     (Akira AJISAKA via jing9)
 
+    HDFS-6731. Run "hdfs zkfc-formatZK" on a server in a non-namenode will cause
+    a null pointer exception. (Masatake Iwasaki via brandonli)
+
 Release 2.5.0 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DFSZKFailoverController.java

@@ -122,6 +122,11 @@ public class DFSZKFailoverController extends ZKFailoverController {
           "HA is not enabled for this namenode.");
     }
     String nnId = HAUtil.getNameNodeId(localNNConf, nsId);
+    if (nnId == null) {
+      String msg = "Could not get the namenode ID of this node. " +
+          "You may run zkfc on the node other than namenode.";
+      throw new HadoopIllegalArgumentException(msg);
+    }
     NameNode.initializeGenericKeys(localNNConf, nsId, nnId);
     DFSUtil.setGenericConf(localNNConf, nsId, nnId, ZKFC_CONF_KEYS);