Hi - Again, hiring a simple VM at a third location without a Solr cloud sounds like the simplest solution. It keeps the quorum tight and sound. This simple solution is the one i would try first.
Or am i completely missing something and sound like an idiot? Could be, of course. Regards, Markus -----Original message----- > From:Jan Høydahl <jan....@cominvent.com> > Sent: Thursday 25th May 2017 0:15 > To: solr-user@lucene.apache.org > Subject: Re: Spread SolrCloud across two locations > > 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 - www.cominvent.com > > > 23. mai 2017 kl. 18.56 skrev Shawn Heisey <elyog...@elyograg.org>: > > > > 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 > > > >
