[jira] [Updated] (ZOOKEEPER-1075) Zookeeper Server cannot join an existing ensemble if the existing ensemble doesn't already have a quorum

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

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-1075?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vishal Kathuria updated ZOOKEEPER-1075:
---------------------------------------

    Attachment: zk1075.txt

This is a simple patch to optimize the case when a server that would restore the quorum is coming up.

Instead of leader giving up and leader election happening, this change will make the new server join the existing ensemble.

> Zookeeper Server cannot join an existing ensemble if the existing ensemble doesn't already have a quorum
> --------------------------------------------------------------------------------------------------------
>
>                 Key: ZOOKEEPER-1075
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1075
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: leaderElection
>    Affects Versions: 3.3.2
>         Environment: Windows 7
>            Reporter: Vishal Kathuria
>         Attachments: zk1075.txt
>
>   Original Estimate: 48h
>  Remaining Estimate: 48h
>
> Here is the sequence of steps that reproduces the problem.
> On a 3 server ensemble,
> 1. Bring up two servers (say 1 and 2). Lets say 1 is leading.
> 2. Bring down 2
> 3. Bring up 2. 
> 4. 2 gets a notification from 1 that it is leading but 2 doesn't accept it as a leader since it cannot find one other node that thinks 1 is the leader.
> So the ensemble gets stuck where 2 isn't following. If at this point, 3 comes up, then one of 2 & 3 will become a leader and 1 will keep thinking it is the leader.
> I am working on a patch to fix this issue.

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