prometheus: Revive the prometheus plugin

[cdecker]

I also added myself as maintainer in the CODEOWNERS file.

[chrisguida]

Excited to see this PR! Will try it out soon :)

[daywalker90]

Tests are flaky, i saw some "address already in use" in one of them.

[chrisguida]

Interesting, looks like this is only broken on 23.11

[chrisguida]

Gonna update the CI to add 24.08 and remove 23.11, then this should be good to go

[chrisguida]

@cdecker any suggestions on how to use this? I'm not familiar with the prometheus protocol.

I think this is fine to merge since this plugin was already in the plugins repo, just archived due to failing tests, which this PR fixes.

ACK 78b17da

[cdecker]

Sure, the plugin just exposes the /metrics URL on a given port (concurrent tests are causing the flakiness), and then you configure your prometheus server to scrape that endpoint, which puts the metrics in its timeseries DB. It's a very lightweight way of collecting metrics in a scalable way.

[mikemoniker]

Taking a look at this, I have a raspiblitz running cln, going to clone the prometheus plugin branch in and run prometheus and point it at the endpoint.

[mikemoniker]

I was able to install prometheus and get it to ingest the metrics and display them on port 9100. I had some difficulties with poetry and raspiblitz.

Since raspiblitz does everything with pip install --user, but I did not find an equivalent for poetry, I had to edit the shebang of the prometheus.py to use the venv python executable. @cdecker, I am curious how you run this on your system. Is there a more reproducible way? So it can be easier for future users.