Critical Description
org.apache.curator.framework.recipes.leader.LeaderLatch#getLeader() throws KeeperException with Code#NONODE intermittently as mentioned in the stack trace below. It may be possible participant's ephemeral ZK node is removed because its connection/session is closed.
You can see the below code at https://github.com/apache/curator/blob/master/curator-recipes/src/main/java/org/apache/curator/framework/recipes/leader/LeaderLatch.java#L451
public Participant getLeader() throws Exception
{
Collection<String> participantNodes = LockInternals.getParticipantNodes(client, latchPath, LOCK_NAME, sorter);
return LeaderSelector.getLeader(client, participantNodes);
}
I guess it hits a race condition where a participant node is retrieved but when it invokes LeaderSelector#getLeader() it would have been removed because of session timeout and it throws KeeperException with NoNode code. It does not retry as the RetryLoop retries only for connection/session timeouts. But in this case, NoNode should have been retried. I could not find any APIs on CuratorClient to configure the kind of KeeperException codes to be retried. It may be good to have a way to take what kind of errors should be retried in org.apache.curator.framework.CuratorFrameworkFactory.Builder APIs.
Intermittent Exception found with the stack trace:
2016-11-15 06:09:33.954 o.a.s.d.nimbus [ERROR] Error when processing event
org.apache.storm.shade.org.apache.zookeeper.KeeperException$NoNodeException: KeeperErrorCode = NoNode for /storm/leader-lock/_c_97c09eed-5bba-4ac8-a05f-abdc4e8e95cf-latch-0000000002
at org.apache.storm.shade.org.apache.zookeeper.KeeperException.create(KeeperException.java:111)
at org.apache.storm.shade.org.apache.zookeeper.KeeperException.create(KeeperException.java:51)
at org.apache.storm.shade.org.apache.zookeeper.ZooKeeper.getData(ZooKeeper.java:1155)
at org.apache.storm.shade.org.apache.curator.framework.imps.GetDataBuilderImpl$4.call(GetDataBuilderImpl.java:304)
at org.apache.storm.shade.org.apache.curator.framework.imps.GetDataBuilderImpl$4.call(GetDataBuilderImpl.java:293)
at org.apache.storm.shade.org.apache.curator.RetryLoop.callWithRetry(RetryLoop.java:108)
at org.apache.storm.shade.org.apache.curator.framework.imps.GetDataBuilderImpl.pathInForeground(GetDataBuilderImpl.java:290)
at org.apache.storm.shade.org.apache.curator.framework.imps.GetDataBuilderImpl.forPath(GetDataBuilderImpl.java:281)
at org.apache.storm.shade.org.apache.curator.framework.imps.GetDataBuilderImpl.forPath(GetDataBuilderImpl.java:42)
at org.apache.storm.shade.org.apache.curator.framework.recipes.leader.LeaderSelector.participantForPath(LeaderSelector.java:375)
at org.apache.storm.shade.org.apache.curator.framework.recipes.leader.LeaderSelector.getLeader(LeaderSelector.java:346)
at org.apache.storm.shade.org.apache.curator.framework.recipes.leader.LeaderLatch.getLeader(LeaderLatch.java:454)
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