Raghu S commented on ZOOKEEPER-107:

Ben, to be honest, I wasn't thinking batch addition/deletion. I was thinking we 
will allow only one node to join or leave the cluster at a time, in which case 
we won't end up in a split brain.

One thing I am still missing is, how do we plan to reconcile the divergence in 
conifguration info during leader election if we use ZAB? With ZAB, we go ahead 
and write to the log as soon as a PROPOSAL is sent. COMMIT is used only to 
notify the servers that the a majority have logged the update and the clients 
can start reading the new update. So I am not really seeing how this will help 
configuration change. Now in the example that you bring up, if D, E and F have 
logged the new view and all the nodes are brought up after a power cycle, a 
split brain could still occur, no? Should we allow only one node to be 
added/deleted at a time?

> Allow dynamic changes to server cluster membership
> --------------------------------------------------
>                 Key: ZOOKEEPER-107
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-107
>             Project: Zookeeper
>          Issue Type: Improvement
>          Components: server
>            Reporter: Patrick Hunt
>         Attachments: SimpleAddition.rtf
> Currently cluster membership is statically defined, adding/removing hosts 
> to/from the server cluster dynamically needs to be supported.

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