No. Zero downtime upgrade (ZDU) is available only for the enterprise editions of Jira,  Jira Software Data Center and Jira Service Management Data Center , versions 7.3 or later.

Yes, you can upgrade to any Jira version after 7.3, as long as you stay within the same platform release, like the 7.x line.

When you choose to skip multiple feature release versions (e.g. 7.3 to 7.6), make sure to test the upgrade in a staging environment. With every release, Atlassian tests the upgrade path from previous version to newest version (upgrading a single feature release version only). Zero downtime upgrade (ZDU), however, doesn’t have any constraints that wouldn’t let it you skip multiple versions during an upgrade.

Yes, you can upgrade to any Jira version after 7.3, as long as you stay within the same platform release, for example the 7.x line.

When you choose to skip multiple versions (e.g. 7.3 to 7.6), make sure to test the upgrade in a staging environment. With every release, we’re testing the upgrade from previous version to current version (upgrading through a single version only), as it’s impossible to test all possible combinations. Zero downtime upgrade (ZDU), however, doesn’t have any constraints that wouldn’t let it go through multiple versions.

No. Zero downtime upgrade (ZDU) isn’t supported for upgrading between platform releases (e.g. between the 7.x line and the 8.x line).

That’s because platform releases introduce fundamental changes to how Jira works, and require a normal upgrade. Once you move to the new platform release line, you can use zero downtime upgrade to upgrade to this platform’s feature and bug fix releases (e.g. from 8.0 to 8.1).

Here’s an overview of the differences between platform, feature, and bug fix releases:

Yes; just like with other upgrade methods, you should always back up your database prior to the upgrade, preferably using the database native tools.

Yes, you can roll back to your previous version at any point before finalizing the upgrade (it’s the last step of the upgrade process).

For the database, the database schema will be updated after you upgrade the first node, and these changes won’t be reverted. This shouldn’t be a problem, though, as schema changes are backward compatible and can work with your previous version.

After  finalizing the upgrade,  a non-upgraded node won’t be allowed to join the cluster, and will be locked on startup. In a case like this, you can shut it down, upgrade the node, and then attempt to rejoin it with the rest of the Data Center cluster.

During the upgrade, each node will be shut down (one at a time), upgraded, and then started again. Once a particular node is unavailable, the traffic and the load will shift to remaining nodes, which could affect performance. We recommend that you don’t schedule your zero downtime upgrade at the same time as your peak traffic hours. However, you can still expect that you will have continuity of service when you choose to run your upgrade using ZDU.

No. In feature and bug fix releases, where zero downtime upgrade (ZDU) is supported, new versions don’t introduce changes that would require an automatic re-index.

We recommend upgrading apps separately, after the Jira Data Center cluster has been upgraded.

During the zero downtime upgrade, Jira freezes all apps for nodes that are still running the original version of Jira. This means that even if you upgrade apps during the upgrade, all Jira nodes that weren’t yet upgraded will continue to run the old version of the apps. Once you upgrade a particular node, it will immediately pick up the upgraded, compatible apps.

If you’re an app developer and need more details, go here.

Yes, you can roll back to your previous version at any point before finalizing the upgrade (it’s the last step of the upgrade process).

For the database, the database schema will be updated after you upgrade the first node, and these changes won’t be reverted. This shouldn’t be a problem, though, as schema changes are backward compatible and can work with your previous version.

Yes. We’re tracking bugs that might affect ZDU on our public Jira instance, all labeled with affects-zdu. You can view them here