Add initial flask app

[cbartz]

Applicable spec: ISD-116 (internal)

Overview

Add the initial flask application. Only the webhook receiving functionality is included. The webhooks are logged into files in a certain directory, which will then be transmitted automatically to Loki using cos integration.

Follow-up PRs will include:

• Webhook validation using secrets
• The 12-factor charm
• Log file rotation
• Log configuration with gunicorn (for app logs, not webhook logs)
• Using poetry (requires Enable poetry workflow operator-workflows#236 to be merged)

Rationale

A webhook router application is required as defined in the specification.

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)

There is no charm yet, so there are no docs on charmhub.

[cbartz]

@weiiwang01 Can you take a look, please? Thanks.

[jdkandersson]

I think it looks good once the comments from Weii are addressed :)

[github-actions]

Test coverage for 4756523

Name         Stmts   Miss Branch BrPart  Cover   Missing
--------------------------------------------------------
src/app.py      32      3      2      1    88%   65-67
--------------------------------------------------------
TOTAL           32      3      2      1    88%

Static code analysis report

Run started:2024-03-12 12:05:53.451122

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 173
  Total lines skipped (#nosec): 3
  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):

[jdkandersson]

I'll put the note here as well, we were looking into this, and it seems there is the gunicorn way available as well: https://www.google.com/url?q=https://trstringer.com/logging-flask-gunicorn-the-manageable-way/&sa=D&source=docs&ust=1710249238666567&usg=AOvVaw210jtoz0IaFpGgAiZ48V_m

[cbartz]

I'll put the note here as well, we were looking into this, and it seems there is the gunicorn way available as well: https://www.google.com/url?q=https://trstringer.com/logging-flask-gunicorn-the-manageable-way/&sa=D&source=docs&ust=1710249238666567&usg=AOvVaw210jtoz0IaFpGgAiZ48V_m

@jdkandersson
Thanks, but regarding the webhook logs, I would like to distinguish between gunicorn/app logs and those to separate them more easily in COS (e.g. to filter just for /var/log/whrouter/*.log filename in Grafana).
Regarding the application logs, this might be the way to go, though I think this should be added once we have the charm code (which is responsible for installing gunicorn and running flask via it).