Comment 2 for bug 1938708

A reproducer for this is quite simple: forcefully powering of a follower (replica) unit and powering it back on results in a unit being blocked with mysql starting but reporting the following in the error.log:

* [Server] Error reading GTIDs from relaylog: -1
* [Repl] Error reading relay log event for channel 'group_replication_applier': corrupted data in log event
* [Repl] Slave SQL for channel 'group_replication_applier': Relay log read failure: Could not parse relay log event entry. The possible reasons are: the master's binary log is corrupted (you can check this by running 'mysqlbinlog' on the binary log), the slave's relay log is corrupted (you can check this by running 'mysqlbinlog' on the relay log), a network problem, the server was unable to fetch a keyring key required to open an encrypted relay log file, or a bug in the master's or slave's MySQL code. If you want to check the master's binary log or slave's relay log, you will be able to know their names by issuing 'SHOW SLAVE STATUS' on this slave. Error_code: MY-013121
* [Repl] Plugin group_replication reported: 'The applier thread execution was aborted. Unable to process more transactions, this member will now leave the group.'
* [Repl] Plugin group_replication reported: 'Fatal error during execution on the Applier process of Group Replication. The server will now leave the group.'
* [Repl] Plugin group_replication reported: '[GCS] The member is already leaving or joining a group.'
* [Repl] Plugin group_replication reported: 'Unable to confirm whether the server has left the group or not. Check performance_schema.replication_group_members to check group membership information.'
* [Repl] Plugin group_replication reported: 'The server was automatically set into read only mode after an error was detected.'
* [Repl] Error running query, slave SQL thread aborted. Fix the problem, and restart the slave SQL thread with "SLAVE START". We stopped at log 'FIRST' position 0
2022-07-18T14:51:17.013502Z 0 [Warning] [MY-011735] [Repl] Plugin group_replication reported: '[GCS] Shutting down an outgoing connection. This happens because something might be wrong on a bi-directional connection to node 10.10.20.32:33061. Please check the connection status to this member'
* [Repl] Plugin group_replication reported: 'There was a previous plugin error while the member joined the group. The member will now exit the group.'

https://paste.ubuntu.com/p/8xPkRDXHDB/ (juju status and error.log before and after power events)

https://paste.ubuntu.com/p/dq2kr7znzv/ (full juju show-status-log for the affected unit)

18 Jul 2022 17:51:23+03:00 juju-unit executing running start hook
18 Jul 2022 17:51:56+03:00 juju-unit executing running leader-settings-changed hook
18 Jul 2022 17:52:24+03:00 juju-unit idle
18 Jul 2022 18:21:55+03:00 workload blocked Cluster is inaccessible from this instance. Please check logs for details.

https://paste.ubuntu.com/p/H83HdMcVQK/ (cluster-status action output)