Configure Finch pools

[patmaddox]

Change description

This adds a finch_pools key to the Grafana config, to be passed as the pools key to Finch.start_link/1.

What problem does this solve?

We connect to our Grafana instance over an HTTP proxy. Configuring a proxy in Finch requires passing connection opts to the underlying Mint library.

Example usage

config :our_app, OurApp.PromEx,
  disabled: false,
  grafana: [
    host: System.fetch_env!("GRAFANA_HOST"),
    auth_token: System.fetch_env!("GRAFANA_API_KEY"),
    finch_pools: %{
      default: [
        conn_opts: [
          proxy: {:http, "localhost", 8080, []}
        ]
      ]
    }
  ],

Additional details and screenshots

This bumps the Finch dependency, because v0.12.0 adds "support for Mint.UnsafeProxy connections". I opted to bump to the latest 0.13.0.

Checklist

• I have added unit tests to cover my changes.
• I have added documentation to cover my changes.
• My changes have passed unit tests and have been tested E2E in an example project.

[patmaddox]

I opted for finch_pools rather than finch: [ pools: ... ] for two reasons:

1. Finch.start_link/1 only defines two options: name and pools. If they add more options at some point, this could get messy - but if that happened, we could consider changing this to just finch.
2. More importantly, PromEx.grafana_client_child_spec/4 passes :name to GrafanaClient.child_spec/, which passes it to Finch.

This would lead to some ambiguity if you did e.g. finch: [ name: MyApp, pools: %{ ... }].

It's possible to address - maybe just set a default name if the Finch options key doesn't exist. I just don't know that it's worth it at this point.

finch: [ pools: ... ] is more future-proof though, and I think would be straightforward to do.

Any preference on which it should be?

[akoutmos]

I think the way that you have it now it fine given that finch doesn't provide any other configuration options that need to be leveraged. Will merge in as soon as CI passes :)

[coveralls]

Coverage increased (+0.1%) to 79.431% when pulling 2e4c646 on patmaddox:finch_pools into c2e0924 on akoutmos:master.