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From "Jack Krupansky" <>
Subject Re: Minimum HA Setup with SolrCloud
Date Thu, 06 Dec 2012 22:25:24 GMT
Slightly more recent link:

-- Jack Krupansky

-----Original Message----- 
From: Jack Krupansky
Sent: Thursday, December 06, 2012 5:21 PM
Subject: Re: Minimum HA Setup with SolrCloud


If 1 is the minimum, what is the 3 "minimum" all about?

The zk web page does say "Three ZooKeeper servers is the minimum recommended
size for an ensemble, and we also recommend that they run on separate
machines" - but it does say "recommended".

But back to the original question - it sounds as if 4 nodes would the
recommended minimum number of nodes if you want to tolerate one machine
going down and maintaining that 3 zookeeper recommended minimum ensemble.

>From the zookeeper web page:

"For reliable ZooKeeper service, you should deploy ZooKeeper in a cluster
known as an ensemble. As long as a majority of the ensemble are up, the
service will be available. Because Zookeeper requires a majority, it is best
to use an odd number of machines. For example, with four machines ZooKeeper
can only handle the failure of a single machine; if two machines fail, the
remaining two machines do not constitute a majority. However, with five
machines ZooKeeper can handle the failure of two machines."


-- Jack Krupansky

-----Original Message----- 
From: Otis Gospodnetic
Sent: Thursday, December 06, 2012 4:39 PM
Subject: Re: Minimum HA Setup with SolrCloud

1 is the minimum :)
2 makes no sense.
3 must be the most common number in the zoo.

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On Thu, Dec 6, 2012 at 9:46 AM, Jack Krupansky

> "but if those same machines are running zookeeper, you need 3."
> And one of those 3 can go down? I thought 3 was the minimum number of
> zookeepers.
> -- Jack Krupansky
> -----Original Message----- From: Mark Miller
> Sent: Thursday, December 06, 2012 9:30 AM
> To:
> Subject: Re: Minimum HA Setup with SolrCloud
> It depends on if you are running embedded zk or an external zk ensemble.
> One leader and a replica is all you need for Solr to allow on machine to
> go down - but if those same machines are running zookeeper, you need 3.
> You could also run zookeeper on one external machine and then it would be
> fine if you lost one solr node - but if you the one external zk node went
> down you would lose the ability to do updates until it was brought back 
> up.
> - Mark
> On Dec 6, 2012, at 2:46 AM, Thomas Heigl <> wrote:
>  Hey all,
>> I'm in the process of migrating a single Solr 4.0 instace to a SolrCloud
>> setup for availability reasons.
>> After studying the wiki page for SolrCloud I'm not sure what the absolute
>> minimum setup is that would allow for one machine to go down.
>> Would it be enough to have one shard with one leader and one replica?
>> Could
>> this setup tolerate one of the instances going down? Or do I need three
>> instance because Zookeeper needs a quorum of instances?
>> Cheers,
>> Thomas

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