Add prom scraper endpoint

[moleske]

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One more attempt at #240
Now we don't set up prom scraper mtls if any scraper property is missing

When cloudfoundry/cf-deployment#970 is merged, we won't need to check if the property is set

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• I have run CF Acceptance Tests on bosh lite

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: dalvarado / name: david (52fbedf)
• ✅ login: moleske / name: M. Oleske (7ed11a1)
• ✅ login: svkrieger / name: Sven Krieger (64c6cd6)

[sethboyles]

@moleske can we think about merging this now that cloudfoundry/cf-deployment#970 is merged?

[moleske]

Yes, we should merge this. I was previously waiting for ruby 3.1 things to be good and then the pipeline to be happy before merging. This is good to go whenever now

[moleske]

/easycla

[svkrieger]

I hope it's okay to directly push into this branch. I tried this out in a cf foundation and I could verify that the metrics got scraped by the prom_scraper job and were forwarded to Loggregator.

I removed all locations from the server config, which accepts the prom_scraper certs, except the metrics endpoint.
nginx will return a 404 if it receives a request on that port, which does not match the location /internal/v4/metrics. Alternatively we could add a default location, which returns a 403 - forbidden.

Additionally I replaced the catch-all server name with the actual internal server name. Will this endpoint be called by other consumers from outside, which might use other server names rather than the internal one? If not, I think we don't need a catch-all server name here.

[moleske]

I hope it's okay to directly push into this branch. I tried this out in a cf foundation and I could verify that the metrics got scraped by the prom_scraper job and were forwarded to Loggregator.

I'm thrilled you're updating this branch! We have not been able to dedicate people to working on this due to shifting priorities. So please go ahead and update to get it working!