3 is the minimum if you want to allow a node to go down. 1 is the minimum if you want the thing to work at all - but if the 1 goes down, ZooKeeper may stop working…
- Mark On Dec 6, 2012, at 2:21 PM, Jack Krupansky <j...@basetechnology.com> wrote: > 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 > -- > Performance Monitoring - http://sematext.com/spm/index.html > Search Analytics - http://sematext.com/search-analytics/index.html > > > > > 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 >>> >> >
