New users sometimes not created for shared-db peers

[Paul Goins]

This is possibly, but not necessarily, related to https://bugs.launchpad.net/charm-percona-cluster/+bug/1906711. The issue did occur at the same time.

I had an issue where a gnocchi unit related to percona-cluster was not able to log in. Upon closer inspection, I saw that while the password had been shared via the relation data, no user record was present in MySQL itself to allow the login from the new unit.

Workaround: I had to manually create the user record in MySQL to allow the logins to work:

  create user '<app name>'@'<app unit ip>' identified by password '<hash copied from user record of peer>'

[Paul Goins (vultaire)]

Actually, the above was not adequate. The above created the missing user, but there's also grants necessary.

[Paul Goins (vultaire)]

Additionally needed:

GRANT ALL PRIVILEGES ON `{db_name}`.* TO '{db_user}'@'{remote_ip}' IDENTIFIED BY '{password}'