Discovery plugin

[SuperQ]

Prometheus now supports built-time plugins.

It would be cool to convert the main package to a discovery plugin so that it could be built-in to Prometheus.

[maxbrunet]

Hey @SuperQ, thank you for letting me know, this sounds interesting.
Although I wonder how many users are building Prometheus from source or are willing to.

My opinion on Go plugins is not fully formed, but it does not seem straight forward to use for anything out-of-tree: https://www.reddit.com/r/golang/comments/b6h8qq/is_anyone_actually_using_go_plugins/ (could be outdated)
Otherwise file_sd has been a good option so far, I think the sidecar pattern is convenient and flexible for most.

I am open to consider a PR that would add this option.

[SuperQ]

Yes, we explored using actual Go plugins a couple times over the years and determined that they were unusable. This is why we went with the compile-time psudo-plugin thing. The compile-time option also means it would be easy to adopt the code in upstream Prometheus if it was popular enough.

Another way to do the sidecar is the new http_sd_configs option. Rather than having to directly attach the SD as a sidecar, you can run it as a separate service that exposes the targets as json over HTTP.

[anarcher]

Support for http_sd_configs would be great! :-)

[maxbrunet]

Thank you for your interest @anarcher, I have created a separate issue for that: #318, PR welcome :)