[HADOOP-9459] ActiveStandbyElector can join election even before Service HEALTHY, and results in null data at ActiveBreadCrumb

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 2.0.2-alpha
• Fix Version/s: 2.1.0-beta
• Component/s: ha
• Hadoop Flags: Reviewed
• Assignee: Vinayakumar B
• Reporter: Vinayakumar B
• Created: 01/Feb/13 12:34
• Updated: 03/Sep/14 22:47
• Resolved: 14/May/13 06:44

Description

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 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

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)

Should not join the election before service is HEALTHY