[jira] [Commented] (SOLR-14371) Zk StatusHandler should know about dynamic zk config

["Jan Høydahl (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-14371?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17073223#comment-17073223 ] 

Jan Høydahl commented on SOLR-14371:
------------------------------------

The PR is now ready for broader review, for those interested.

Since embedded ZK and ZK in tests are hardcoded to a standalone variant, and big code changes are needed to spin up a Quorum, there are no unit tests for the new {{getConfig()}} method in {{SolrZkClient}}. I have tested manually with an external zk cluster that it works though.

Here is a condensed summary of the current PR

* If zk quorum has dynamic reconfiguration, the ZkStatus handler and Admin UI view will now display info for each of the currently active Zookeepers, even if they differ from initial ZK_HOST
* That meanns you can configure ZK_HOST with a single LB address in front of all ZKs (like Solr Operator for k8s) and it will "just work"
* New info in JSON response and UI: {{dynamicReconfig=true/false}}
* New info for each ZK host: {{role=participant/follower}}


> Zk StatusHandler should know about dynamic zk config
> ----------------------------------------------------
>
>                 Key: SOLR-14371
>                 URL: https://issues.apache.org/jira/browse/SOLR-14371
>             Project: Solr
>          Issue Type: Bug
>      Security Level: Public(Default Security Level. Issues are Public) 
>            Reporter: Jan Høydahl
>            Assignee: Jan Høydahl
>            Priority: Major
>          Time Spent: 50m
>  Remaining Estimate: 0h
>
> With zk 3.5 it supports dynamic reconfig, which is used by the solr-operator for Kubernetes. Then Solr is given a zkHost of one url pointing to a LB (Service) in front of all zookeepers, and the zkclient will then fetch list of all zookeepers from special zknode /zookeeper/config and reconfigure itself with connection to all zk nodes listed. So you can then scale up/down number of zk nodes dynamically without restarting solr.
> However, the Admin UI displays errors since it believes it is connected to only one zk, which is contradictory to what zk itself reports. We need to make ZookeeperStatusHandler aware of dynamic reconfig so it asks zkclient what current zkHost is instead of relying on Zk_HOST static setting.



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