MySQL backups not working on some environments where alternative methods did in the past

[Paul Goins]

I'm trying to run:

  juju-backup-all -l info -A -o <BACKUP_DIR> --exclude-controller-backup

However, the MySQL backup doesn't work:

  2022-02-28 22:40:41,026 ERROR jujubackupall.process [foundations-maas openstack mysql] App backup not completed: ['action "set-pxc-strict-mode" not defined on unit "mysql/0"'].

The mysql charm deployed is percona-cluster-286, which lacks that action.

We have a different script already in place which is successfully backing up mysql. It's using this procedure to back things up successfully:

* juju run-action -m <model> --wait <mysql-unit> backup compress=True"
* juju ssh -m <model> <mysql-unit> 'sudo tar -zcf /opt/backups/mysqlbackup.tar.gz --remove-files /opt/backups/mysql'
* juju scp -m <model> <mysql-unit>:/opt/backups/mysqlbackup.tar.gz <local_path>/mysql-<date>.tar.gz

However, I can see that the charm here expects newer behavior, relying on the set-pxc-strict-mode and mysqldump actions instead.

This bug may be primarily documenting the issue; I'm not sure if we actually want to provide support for older charms such as this one, or instead encourage users to upgrade to newer versions of charms. Perhaps the fix is a version check on the percona-cluster charm to ensure it's new enough to run the actions this charm expects?