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https://issues.apache.org/jira/browse/SOLR-10284?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15938890#comment-15938890
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Ben DeMott commented on SOLR-10284:
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bq. Keep it simple? boolean allowStandaloneZk = numZkHosts == 1;
Totally agree, just wasn't sure if there were any corner cases that this would
disagree with, sounds like a plan.
I'll update here with my progress on the patch and any further notes/questions.
Thanks for the input.
> Solr connection to Standalone node in Ensemble causes cluster failure
> ---------------------------------------------------------------------
>
> Key: SOLR-10284
> URL: https://issues.apache.org/jira/browse/SOLR-10284
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Components: SolrCloud
> Affects Versions: 6.3, 6.4
> Environment: Solrcloud, with Zookeeper <any version>
> Reporter: Ben DeMott
>
> I posted this issue on the Dev mailing list and was encouraged to create a
> Jira ticket. This isn't a bug per-se.
> Solr connects / reconnects to "Standalone" Zookeeper nodes, within an
> ensemble cluster, which causes absolute havoc.
> I work for Dice.com, as one of the core search developers.
> I'm happy to write a patch, as we'll probably do that internally anyways. I
> just want to get consensus from the community about how to provide the best
> solution.
> My original email describing the issue:
> http://mail-archives.apache.org/mod_mbox/lucene-dev/201703.mbox/raw/%3CCACbtCQ2cSPA8NbnqCbXZE9nZdT40xFHjpUhAOqUnd%3DqZaRMEsA%40mail.gmail.com%3E/2
> Proposed Solution:
> My thought was an explicit setting in solr.in.sh "ZK_STANDALONE" (which would
> default to TRUE for the solr.in.sh file found next to bin/solr). Upon
> connection or reconnection of the Zookeeper Client, it would ask the server
> "are you standalone", and disconnect if it is and ZK_STANDALONE=false, and
> try the next host. If all hosts are in standalone, an error would be shown -
> "No zookeeper hosts available, that aren't in standalone operation - The
> setting ZK_STANDALONE=false prevents connecting to a standalone Zookeeper"
> In order to urge users to use the setting, I would possibly also have a
> warning shown in the logs, if your ZK_HOSTS is set, has multiple hosts in the
> connection string, and ZK_STANDALONE is not false.
> I can't think of any implicit way to internalize a setting.... Other than....
> ZK_HOSTS connection string setting has multiple hosts, there should be no
> scenario in which any node is standalone, so you could assume there should be
> no standalone servers. But maybe an explicit setting is preferable.
> This solution should be:
> 1.) backwards compatible
> 2.) have very little performance impact (1 extra call upon connection to ZK)
> 3.) isolated to one part of the code.
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