[SOLR-17096] Support for Cluster Singleton plugins in solr.xml

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 9.5
• Component/s: Plugin system
• Assignee: Unassigned
• Reporter: Paul McArthur
• Created: 04/Dec/23 18:07
• Updated: 23/Jul/24 18:00
• Resolved: 18/Jan/24 19:12

Description

How-to: use <clusterSingleton name="myClusterSingleton" class="com.acme.MyClusterSingleton"/>
And set the config solr.cluster.plugin.edit.enabled to false, thus disabling mutable cluster plugins in ZK.

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This issue is related to, and follows on from SOLR-15782.

It should be possible to install and manage the configuration of a cluster singleton plugin in an immutable deployment of SolrCloud. SOLR-15782 discusses the merits of declaring such plugin configurations in solr.xml, and it's implementation provides scope to declare the Replica Placement plugin there.

 

While this approach could work generally for plugins with associated factories that are used to create instances of the plugin when required at runtime  (like the Replica Placement Plugin), it does not provide a solution for cluster singleton plugins which are only instantiated by having a configuration declared in the ZooKeeper cluster properties, which are managed solely by invocation of the /cluster/plugin edit APIs.

It is undesirable to invoke the /cluster/plugin edit APIs with an immutable deployment, and instead any modification to the cluster singleton configurations should occur via a new deployment with the changes declared in solr.xml

Issue Links

• causes: SOLR-17377 ClusterSingleton defined in solr.xml cannot be loaded from a module
• is related to: SOLR-15782 Configure custom node/container handlers in solr.xml
• links to: GitHub Pull Request #2126