Note: All commands are written for juju >= v.3.0
If you are using an earlier version, check the Juju 3.0 Release Notes.
Perform a minor rollback
Example: MySQL 8.0.34 → MySQL 8.0.33
(including charm revision bump: e.g Revision 43 → Revision 42)
After a juju refresh, if there are any version incompatibilities in charm revisions, its dependencies, or any other unexpected failure in the upgrade process, the process will be halted and enter a failure state.
Even if the underlying MySQL cluster continue to work, it’s important to roll back the charm to a previous revision so that an update can be attempted after further inspection of the failure.
Warning: Do NOT trigger rollback during the running upgrade action! It may cause an unpredictable MySQL cluster state!
Summary of the rollback steps
- Prepare the Charmed MySQL application for the in-place rollback.
- Roll back. Once started, all units in a cluster will be executed sequentially. The rollback will be aborted (paused) if the unit rollback has failed.
- Check. Make sure the charm and cluster are in healthy state again.
Step 1: Prepare
To execute a rollback, we use a similar procedure to the upgrade. The difference is the charm revision to upgrade to. In this guide’s example, we will refresh the charm back to revision 182.
It is necessary to re-run pre-upgrade-check action on the leader unit in order to enter the upgrade recovery state:
juju run mysql/leader pre-upgrade-check
Step 2: Rollback
When using charm from charmhub:
juju refresh mysql --revision=182
When deploying from a local charm file, one must have the previous revision charm file and run the following command:
juju refresh mysql --path=./mysql_ubuntu-22.04-amd64.charm
where
mysql_ubuntu-22.04-amd64.charmis the previous revision charm file.
The first unit will be rolled out and should rejoin the cluster after settling down. After the refresh command, the juju controller revision for the application will be back in sync with the running Charmed MySQL revision.
Step 3: Check
Future improvements are planned to check the state on pods/clusters on a low level.
For now, check juju status to make sure the cluster state is OK.