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From Pushkar Raste <>
Subject Re: Spread SolrCloud across two locations
Date Wed, 24 May 2017 22:35:19 GMT
A setup I have used in the past was to have an observer I  DC2. If DC1 one
goes boom you need manual intervention to change observer's role to make it
a follower.

When DC1 comes back up change on instance in DC2 to make it a observer

On May 24, 2017 6:15 PM, "Jan Høydahl" <> wrote:

> Sure, ZK does by design not support a two-node/two-location setup. But
> still, users may want/need to deploy that,
> and my question was if there are smart ways to make such a setup as little
> painful as possible in case of failure.
> Take the example of DC1: 3xZK and DC2: 2xZK again. And then DC1 goes BOOM.
> Without an active action DC2 would be read-only
> What if then the Ops personnel in DC2 could, with a single script/command,
> instruct DC2 to resume “master” role:
> - Add a 3rd DC2 ZK to the two existing, reconfigure and let them sync up.
> - Rolling restart of Solr nodes with new ZK_HOST string
> Of course, they would also then need to make sure that DC1 does not boot
> up again before compatible change has been done there too.
> --
> Jan Høydahl, search solution architect
> Cominvent AS -
> > 23. mai 2017 kl. 18.56 skrev Shawn Heisey <>:
> >
> > On 5/23/2017 10:12 AM, Susheel Kumar wrote:
> >> Hi Jan, FYI - Since last year, I have been running a Solr 6.0 cluster
> in one of lower env with 6 shards/replica in dc1 & 6 shard/replica in dc2
> (each shard replicated cross data center) with 3 ZK in dc1 and 2 ZK in dc2.
> (I didn't have the availability of 3rd data center for ZK so went with only
> 2 data center with above configuration) and so far no issues. Its been
> running fine, indexing, replicating data, serving queries etc. So in my
> test, setting up single cluster across two zones/data center works without
> any issue when there is no or very minimal latency (in my case around 30ms
> one way
> >
> > With that setup, if dc2 goes down, you're all good, but if dc1 goes
> down, you're not.
> >
> > There aren't enough ZK servers in dc2 to maintain quorum when dc1 is
> unreachable, and SolrCloud is going to go read-only.  Queries would most
> likely work, but you would not be able to change the indexes at all.
> >
> > ZooKeeper with N total servers requires int((N/2)+1) servers to be
> operational to maintain quorum.  This means that with five total servers,
> three must be operational and able to talk to each other, or ZK cannot
> guarantee that there is no split-brain, so quorum is lost.
> >
> > ZK in two data centers will never be fully fault-tolerant. There is no
> combination of servers that will work properly.  You must have three data
> centers for a geographically fault-tolerant cluster.  Solr would be
> optional in the third data center.  ZK must be installed in all three.
> >
> > Thanks,
> > Shawn
> >

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