Rework handling of the pebble_ready event

[nrobinaubertin]

Overview

We discovered that in cases where the workload container gets restarted on its own, only a pebble_ready event would be thrown by juju and the container would not be correctly re-planned.
This PR handles pebble_ready event correctly and adds a named function for each event we listen to. This is a step towards "managing charm complexity", allows us to have more fine grained logging and handling of events.
During the creation of the PR, it was noted that the redis_relation_changed handler didn't try to setup discourse as needed, so it was added.

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation is generated using src-docs
• The documentation for charmhub is updated.
• The PR is tagged with appropriate label (urgent, trivial, complex)

[amandahla]

Out of curiosity: From the doc Lifecycle events, while deploying the charm, this happens: install -> config-changed -> start -> -pebble-ready

Would this make the set up discourse run twice?

[nrobinaubertin]

Out of curiosity: From the doc Lifecycle events, while deploying the charm, this happens: install -> config-changed -> start -> -pebble-ready

Would this make the set up discourse run twice?

Yes, indeed. This is probably why it is subject to timeouts here. I need to fix this

[jdkandersson]

Thanks for taking a step towards moving discourse to be compliant with the architecture guidance

[merkata]

Looks good, the comments are worth having a look at.

[amandahla]

While reading this I was thinking: "why not handle only pebble ready event?"

[nrobinaubertin]

While reading this I was thinking: "why not handle only pebble ready event?"

The pebble ready event can occur when the relations don't exist or are not ready. So if we don't defer, it doesn't allow us to be sure that the charm will go through the setup

[yanksyoon]

LGTM, minor comments and questions. Thank you!

[github-actions]

Test coverage for 4ebe987

Name              Stmts   Miss Branch BrPart  Cover   Missing
-------------------------------------------------------------
src/charm.py        324     32     84     12    89%   137, 163, 173, 181-182, 338->343, 526-528, 533-534, 545-547, 552-553, 565-567, 572-573, 585-587, 612-614, 654->exit, 664->exit, 694-700, 726->exit, 740-741, 751->exit, 765
src/database.py      30      1      8      1    95%   56
-------------------------------------------------------------
TOTAL               354     33     92     13    90%

Static code analysis report

Run started:2023-11-29 15:16:08.049764

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 1903
  Total lines skipped (#nosec): 1
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
  Total issues (by severity):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
  Total issues (by confidence):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
Files skipped (0):