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From Hans Jespersen <h...@confluent.io>
Subject Re: Having 4 Node Kafka Cluster
Date Mon, 06 Mar 2017 11:20:48 GMT
Jens,

I think you are correct that a 4 node zookeeper ensemble can be made to work but it will be
slightly less resilient than a 3 node ensemble because it can only tolerate 1 failure (same
as a 3 node ensemble) and the likelihood of node failures is higher because there is 1 more
node that could fail.
So it SHOULD be an odd number of zookeeper nodes (not MUST).

-hans


> On Mar 6, 2017, at 12:20 AM, Jens Rantil <jens.rantil@tink.se> wrote:
> 
> Hi Hans,
> 
>> On Mon, Mar 6, 2017 at 12:10 AM, Hans Jespersen <hans@confluent.io> wrote:
>> 
>> A 4 node zookeeper ensemble will not even work. It MUST be an odd number
>> of zookeeper nodes to start.
> 
> 
> Are you sure about that? If Zookeer doesn't run with four nodes, that means
> a running ensemble of three can't be live-migrated to other nodes (because
> that's done by increasing the ensemble and then reducing it in the case of
> 3-node ensembles). IIRC, you can run four Zookeeper nodes, but that means
> quorum will be three nodes, so there's no added benefit in terms of
> availability since you can only loose one node just like with a three node
> cluster.
> 
> Cheers,
> Jens
> 
> 
> -- 
> Jens Rantil
> Backend engineer
> Tink AB
> 
> Email: jens.rantil@tink.se
> Phone: +46 708 84 18 32
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> 
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