Jira should remove old jar files of plugins from the shared home as part of an upgrade task when using ZDU

Problem Definition

Plugins jar files that are used by Jira Data Center are located in <jira-shared-home>/plugins/installed-plugins folder.
The jar files located there are copied to each node during startup to the plugins cache.

During zero downtime upgrades (ZDU), Jira won't delete old files from the <jira-shared-home>/plugins/installed-plugins, since other nodes may still use these files.
During startup you may notice entries in the atlassian-jira.log similar to the below:

2021-08-17 17:01:20,480-0300 localhost-startStop-1 INFO      [c.a.j.application.install.PluginBundleInstaller] Application plugin '/shared-home/plugins/installed-plugins/jira-transition-triggers-plugin-8.5.9.jar' is currently locked by an in-progress Zero Downtime Upgrade, skipping clean up of old version

If you rely on ZDU since it was introduced, you may have more than 5 jar files of the same plugin on <jira-shared-home>/plugins/installed-plugins which are copied to each node during startup.

Suggested Solution

On ZDU, upgrade tasks are executed after all nodes are on the target version.
There should be an upgrade task to delete old files from <jira-shared-home>/plugins/installed-plugins, keeping only current ones.

Workaround

Review files <jira-shared-home>/plugins/installed-plugins folder and manually delete the old (duplicates) jar files.
Perform a rolling restart, clearing the plugins cache on each node.

Run the following on each node.

1. Stop Jira following your standard procedure.
2. Delete the following folders.

   <jira-local-home>/plugins/.bundled-plugins
   <jira-local-home>/plugins/.osgi-plugins
   

3. Start Jira following your standard procedure.