Add support for writing to a generic remote_write endpoint in Ruler

[GiedriusS]

Is your feature request related to a problem? Please describe.

I would like to use Cortex Ruler in a Thanos stack. Right now the Ruler component writes to ingesters in the ring.

Describe the solution you'd like

Cortex Ruler should be able to write directly to a generic remote_write endpoint.

Maybe the <ruler_config> configuration could look like this:

remote_write:
  url: "http://127.0.0.1/api/v1/receive"
  headers:
    a: b
  .. any extra things

And if this is provided it would only write through remote_write?

Describe alternatives you've considered

Implementing everything needed to make Thanos Receive ingesters behave like Cortex ones but that's a huge project by itself. Let's start small and add support for just remote writing in Cortex Ruler.

Additional context

Other issue on Thanos side: thanos-io/thanos#7905

[friedrichg]

I see great possibilities with this 🪄

are you willing to do first small PR for this? @GiedriusS

[GiedriusS]

Yes, will work on it 👍

[stale]

This issue has been automatically marked as stale because it has not had any activity in the past 60 days. It will be closed in 15 days if no further activity occurs. Thank you for your contributions.

[GiedriusS]

Bump