[ https://issues.apache.org/jira/browse/HDFS-4463?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Colin Patrick McCabe moved HADOOP-9275 to HDFS-4463:
----------------------------------------------------

          Component/s:     (was: ha)
                       ha
    Affects Version/s:     (was: 2.0.2-alpha)
                       2.0.2-alpha
                  Key: HDFS-4463  (was: HADOOP-9275)
              Project: Hadoop HDFS  (was: Hadoop Common)
    
> ActiveStandbyElector can join election even before Service HEALTHY, and results in null data at ActiveBreadCrumb
> ----------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-4463
>                 URL: https://issues.apache.org/jira/browse/HDFS-4463
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: ha
>    Affects Versions: 2.0.2-alpha
>            Reporter: Vinay
>            Assignee: Vinay
>            Priority: Critical
>
> ActiveStandbyElector can store null at ActiveBreadCrumb in the below race condition. At further all failovers will fail resulting NPE.
> 1. ZKFC restarted.
> 2. due to less machine busy, first zk connection is expired even before the health monitoring returned the status.
> 3. On re-establishment transitionToActive will be called, at this time appData will be null,
> 4. So now ActiveBreadCrumb will have null.
> 5. After this any failovers will fail throwing 
> {noformat}java.lang.NullPointerException
> 	at org.apache.hadoop.util.StringUtils.byteToHexString(StringUtils.java:171)
> 	at org.apache.hadoop.ha.ActiveStandbyElector.fenceOldActive(ActiveStandbyElector.java:892)
> 	at org.apache.hadoop.ha.ActiveStandbyElector.becomeActive(ActiveStandbyElector.java:797)
> 	at org.apache.hadoop.ha.ActiveStandbyElector.processResult(ActiveStandbyElector.java:475)
> 	at org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:545)
> 	at org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:497){noformat}
> Should not join the election before service is HEALTHY

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