[jira] [Created] (HADOOP-9275) ActiveStandbyElector can join election even before Service HEALTHY, and results in null data at ActiveBreadCrumb

["Vinay (JIRA)" <ji...@apache.org>]

Vinay created HADOOP-9275:
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             Summary: ActiveStandbyElector can join election even before Service HEALTHY, and results in null data at ActiveBreadCrumb
                 Key: HADOOP-9275
                 URL: https://issues.apache.org/jira/browse/HADOOP-9275
             Project: Hadoop Common
          Issue Type: Bug
    Affects Versions: 2.0.2-alpha
            Reporter: Vinay
            Assignee: Vinay


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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