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From Shawn Heisey <apa...@elyograg.org>
Subject Re: Zookeeper Ensemble Automation
Date Thu, 05 Jan 2017 20:41:16 GMT
On 1/5/2017 11:19 AM, Washko, Daniel wrote:
> Thanks for the reply Shawn. I would like to clarify something though.
> Right now, the Dynamic Reconfiguration of Zookeeper works for
> Zookeeper – that is adding/removing nodes automatically without having
> to reconfigure each zookeeper node manually. Once Zookeeper is out of
> Alpha then Solr will be updated to take advantage of the Dynamic
> Reconfiguration capability of Zookeeper and auto-discover any changes.
> Is that correct?

I am not sure whether my understanding is correct, but if it is, then I
don't think a zookeeper 3.4.x client (like the one in Solr) will notice
that the server list (with servers running 3.5.x) has changed. 
Depending on exactly how the membership changed, the SolrCloud instance
might not be able to maintain a viable ZK quorum.  If it loses quorum,
SolrCloud goes read-only.

After ZK 3.5 goes through the beta phase and reaches stable, then Solr
will get the upgrade, and we will make sure that the dynamic
reconfiguration works.  It's a feature that we definitely want, though
we may wait for the second or third stable release before we upgrade to
be absolutely certain that it's solid.

There are a couple of questions I do not know the answer to:  1) Whether
any code changes will be required in Solr to take advantage of dynamic
reconfiguration after the dependency upgrade.  2) Whether a Solr
instance with the 3.5 client could be told about only one ZK server,
then discover the whole cluster and connect to all the servers.  Can a
more knowledgeable member of this community answer these questions for me?


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