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https://issues.apache.org/jira/browse/ZOOKEEPER-2988?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16458844#comment-16458844
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Brian Nixon commented on ZOOKEEPER-2988:
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[~hanm] thanks for merging it to 3.5 too, I'll shut down that second pr. This
bug is applicable to 3.4 as well - imo it's a worse danger on that branch since
its easy for configuration files to be stale. I'll fix up pr 478 for the 3.4
branch to reflect the comments I got on pr 476 so it can be ready for review.
> NPE triggered if server receives a vote for a server id not in their voting
> view
> --------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-2988
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2988
> Project: ZooKeeper
> Issue Type: Bug
> Components: leaderElection
> Affects Versions: 3.5.3, 3.4.11
> Reporter: Brian Nixon
> Assignee: Brian Nixon
> Priority: Minor
> Fix For: 3.5.4, 3.6.0
>
>
> We've observed the following behavior in elections when a node is lagging
> behind the quorum in its view of the ensemble topology.
> - Node A is operating with node B in its voting view, but without view of
> node C.
> - B votes for C.
> - A then switches its vote to C, but throws a NPE when attempting to connect.
> This causes the QuorumPeer to spin up a Follower only to immediately have it
> shutdown by the exception.
> Ideally, A would not advertise a vote for a server that it will not follow.
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