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https://issues.apache.org/jira/browse/SOLR-17519?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17912145#comment-17912145
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David Smiley commented on SOLR-17519:
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bq. (ZK) so this probably was never an issue even with nodes movements or
migrations
Yes; assuming the ZK nodes are stable.
Another reason to exclusively use the configured Solr URLs (s) is that the
operator might want to use a load balancer (may even _already_ be using one),
not actually directly a Solr node itself. It might be a single dependable URL.
> CloudSolrClient with HTTP ClusterState can forget live nodes and then fail
> --------------------------------------------------------------------------
>
> Key: SOLR-17519
> URL: https://issues.apache.org/jira/browse/SOLR-17519
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Components: SolrCloud, SolrJ
> Reporter: David Smiley
> Priority: Major
> Labels: newdev, pull-request-available
> Time Spent: 2h
> Remaining Estimate: 0h
>
> When using CloudSolrClient with HTTP URLs to Solr for the cluster state:
> If all live nodes disappear temporarily (hard cluster restart?), the client
> can permanently fail to talk to the cluster, and thus would need to be
> restarted to recover.
> Credit [~ilan] on the dev list:
> {quote}The current implementation removes non live nodes from the set of
> nodes to connect to. Getting the live nodes requires connecting to a specific
> node in the cluster that is therefore live when that happens. Worst case, if
> there is a single node up in the cluster, the client ends with a single node
> in its connection candidates list. For the issue to manifest, that Solr node
> then has to go down. Subsequently, even if other nodes are up, the client
> only has the address of a down node and can't connect.
> The fix is not a big deal. Nodes initially passed as configuration to the
> client should never be removed from the set of candidate nodes to connect to,
> even if they are not live. Other live nodes could be added to that set (and
> removed from it if we so desire when they are no longer live) to increase
> resiliency in case the cluster does have live nodes but all initially
> configured nodes are not live. The design issue is treating the configured
> set of nodes to connect to and the set of live nodes as one thing.
> {quote}
> See org.apache.solr.client.solrj.impl.BaseHttpClusterStateProvider
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