It is not possible to upgrade Jira using Zero downtime upgrade method (ZDU) between major releases (example: from version 7.x to 8.x or from version 8.x to 9.x)

The documentation does not make this limitation clear. This is currently in the header of the documentation:

https://confluence.atlassian.com/adminjiraserver/upgrading-jira-data-center-with-zero-downtime-938846953.html

Zero downtime upgrade is not available when upgrading from Jira 7.x to Jira 8.x. You'll need to use one of the regular methods. If you're already on Jira 8.x, you can use zero downtime to upgrade to any later version.

The text above is misleading and can indicate to customers that it is OK to ZDU from 8.x to 9.x which is not the case. Customers that attempts to perform a ZDU from 8.x to 9.x will receive the following error and upgrade won't complete:

2022-10-22 18:37:26,709-0700 main ERROR [c.a.jira.startup.LauncherContextListener] Unable to start JIRA. java.lang.IllegalStateException: Your node with Jira version 9.3.0 will not start up with version 8.22.4 because Jira does not support zero downtime upgrades between major releases. See https://docs.atlassian.com/jira/jadm-docs-080/Upgrading+Jira+applications. at com.atlassian.jira.startup.ClusterNodeVersionCheckLauncher.verifyMajorVersion(ClusterNodeVersionCheckLauncher.java:85) at com.atlassian.jira.startup.ClusterNodeVersionCheckLauncher.start(ClusterNodeVersionCheckLauncher.java:71) at com.atlassian.jira.startup.DefaultJiraLauncher.lambda$postDbLaunch$2(DefaultJiraLauncher.java:142) at com.atlassian.jira.config.database.DatabaseConfigurationManagerImpl.doNowOrEnqueue(DatabaseConfigurationManagerImpl.java:307)

Expected behaviour

Improve Jira Zero Downtime Upgrade (ZDU) documentation to make it clear the limitation to use ZDU between major releases