DPE-5540 Skip plugin install for not file found

[paulomach]

Issue

1. config_change hook will try to install plugins if configuration diff so indicates, even if plugins files are not available.
2. admin address enabled charms revisions will fail to connect to mysqld case it's not restarted

Case:
refresh ran without pre-upgrade-check - so snap is not updated (no plugin files) but config changed is triggered.

Solution

1. Check for plugin file before try install. Skip if file not found
2. Ensure mysqld restarts on post refresh config_change event

[shayancanonical]

looks good. still confused about the symptoms of the issue - if the charm would enter an error state previously, i would recommend adding a test that runs upgrade without pre-upgrade-check to ensure that things start up normally. thoughts?

[carlcsaposs-canonical]

looks good short-term

when adding refresh v3, would recommend not modifying plugins while a refresh is in progress

[taurus-forever]

LGTM here, ACK to Shayan: adding a test to run refresh without pre-upgrade-check will help us returning here for the following candidate revisions.

[taurus-forever]

... if the charm would enter an error state previously...

Yes, see https://warthogs.atlassian.net/browse/DPE-5540

Update: the ticket has no juju status output and I do not remeber the state. Will post better ticket the next time. AFAIK, refresh was in error state, yes.

[paulomach]

looks good. still confused about the symptoms of the issue - if the charm would enter an error state previously, i would recommend adding a test that runs upgrade without pre-upgrade-check to ensure that things start up normally. thoughts?

You are right. I will include a test before merge