Prometheus resource limitation?

disclaimer: I haven’t try it out yet. planning to move from heroku to here. :man_bowing:t2: just doing a POC now.

I have read this instrumentation (Metrics on Fly · Fly Docs) and it said that we can have custom metrics on my own apps. I don’t have much, it’s around 100-ish metrics.

I want to know pricing plan for Prometheus? if it’s 100% free, how long are logs kept? or the safest way to permanently keep those data is having my own self-hosted prometheus and loki :smiling_face_with_tear:

Same question asking here but no-one answer (Logging retention policies).