Rewind.
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."
See:
http://zookeeper.apache.org/doc/r3.1.2/zookeeperAdmin.html
-- Jack Krupansky
-----Original Message-----
From: Otis Gospodnetic
Sent: Thursday, December 06, 2012 4:39 PM
To: solr-user@lucene.apache.org
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.
Otis
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On Thu, Dec 6, 2012 at 9:46 AM, Jack Krupansky
<j...@basetechnology.com>wrote:
"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: solr-user@lucene.apache.org
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 <tho...@umschalt.com> 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
