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From "Sundaram, Dinesh" <>
Subject RE: Solrcloud with Master/Slave
Date Fri, 05 Jan 2018 17:12:24 GMT
Thanks Shawn and Erick. I guess now we are in same track. So two independent solrcloud nodes
are allowed to sync up via master/slave method without referring any external/embedded zookeepers.
I need to use -cloud in the command while starting solr otherwise I'm not able to see the
admin console. That console is really cool for tracking solr activities.

Dinesh Sundaram
MBS Platform Engineering


-----Original Message-----
From: Erick Erickson []
Sent: Friday, January 5, 2018 10:58 AM
To: solr-user <>
Subject: Re: Solrcloud with Master/Slave

One slight correction. Solr will run perfectly fine with a single ZooKeeper.
The recommendation for 3 is that running with a single ZooKeeper creates a single point of
failure, i.e. if that node goes down for any reason your Solr cluster won't be able to update
anything at all. You can still query, maybe, for a while.

Two ZooKeepers will also run, but as Shawn says that's essentially totally wasting one of
them as it doesn't buy you anything and makes your system _less_ robust.


On Fri, Jan 5, 2018 at 7:57 AM, Shawn Heisey <> wrote:

> On 1/4/2018 9:01 AM, Sundaram, Dinesh wrote:
> > Thanks Shawn for your prompt response. Assume I have solrcloud A
> > server
> with 1 node runs on 8983 port and solrcloud B server with 1 node runs
> on 8983, here I want to synch up the collection between solrcloud A
> and B using the below replication handler. Is this advisable to use at
> the solrcloud B ?
> >
> > <requestHandler name="/replication" class="solr.ReplicationHandler" >
> >     <lst name="slave">
> >         <str name="masterUrl">
> >         <str name="pollInterval">00:00:20</str>
> >     </lst>
> > </requestHandler>
> One of the things I said in my last reply, at the beginning of a
> paragraph so it should have been quite prominent, was "you can't mix
> master-slave replication and SolrCloud."  What part of that was not clear?
> You need to be running standalone mode (not cloud) if you want to use
> master-slave replication.
> When things are set up correctly, SolrCloud will automatically keep
> multiple replicas in sync, and copy the index to new replicas when
> they are created.  There is no need to manage it with replication config.
> For replicating from one SolrCloud cluster to another, there is CDCR
> as Erick described.
> Another thing Erick mentioned:  What you actually have when you start
> Solr the way you did is two completely independent SolrCloud clusters,
> each of which only has one Solr server.  Each solr instance is running
> a zookeeper server embedded within it.  There is no redundancy or
> fault tolerance of any kind.
> If you want to run a fault-tolerant SolrCloud, you will need three
> separate servers.  The smallest possible setup would have both Solr
> and ZooKeeper running on two of those servers (as separate processes).
> The Solr instances would be started with a -z option (or the ZKHOST
> environment variable) to locate the three ZK servers, and without the
> -cloud option.  The third server, which can be a much smaller system,
> would only run ZooKeeper.  You may also need a load balancer,
> depending on what software your clients are using.
> The requirement of three servers comes from ZooKeeper, not Solr.  A
> two-server ZK ensemble is actually *less* reliable than a single
> server, so it's not recommended.  I don't know if they even allow such
> a setup to work.
> Thanks,
> Shawn
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