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https://issues.apache.org/jira/browse/ZOOKEEPER-2189?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14570286#comment-14570286
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Hongchao Deng commented on ZOOKEEPER-2189:
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I think they are talking about a central registry to contain server list. Just
like "discovery.etcd.io" or DMV...
However, this is like asking the root of root. ZK is the root of knowledge for
most distributed systems. Are we expecting a root for ZK too?
Anyway, JIRA is moved to ZOOKEEPER-2203. Let's move discussion there. Do me a
favor and let me clean up the mess caused by my mistake...
> multiple leaders can be elected when configs conflict
> -----------------------------------------------------
>
> Key: ZOOKEEPER-2189
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2189
> Project: ZooKeeper
> Issue Type: Bug
> Components: leaderElection
> Affects Versions: 3.5.0
> Reporter: Akihiro Suda
>
> This sequence leads the ensemble to a split-brain state:
> * Start server 1 (config=1:participant, 2:participant, 3:participant)
> * Start server 2 (config=1:participant, 2:participant, 3:participant)
> * 1 and 2 believe 2 is the leader
> * Start server 3 (config=1:observer, 2:observer, 3:participant)
> * 3 believes 3 is the leader, although 1 and 2 still believe 2 is the leader
> Such a split-brain ensemble is very unstable.
> Znodes can be lost easily:
> * Create some znodes on 2
> * Restart 1 and 2
> * 1, 2 and 3 can think 3 is the leader
> * znodes created on 2 are lost, as 1 and 2 sync with 3
> I consider this behavior as a bug and that ZK should fail gracefully if a
> participant is listed as an observer in the config.
> In current implementation, ZK cannot detect such an invalid config, as
> FastLeaderElection.sendNotification() sends notifications to only voting
> members and hence there is no message from observers(1 and 2) to the new
> voter (3).
> I think FastLeaderElection.sendNotification() should send notifications to
> all the members and FastLeaderElection.Messenger.WorkerReceiver.run() should
> verify acks.
> Any thoughts?
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