Switch to PromEx for prometheus metrics

Recommending use of the separate HTTP server for exposing the metrics
and securing it externally on your firewall or reverse proxy. It will
listen on port 4021 by default.

lib/pleroma/application.ex

@@ -54,7 +54,6 @@ defmodule Pleroma.Application do
     Config.DeprecationWarnings.warn()
     Pleroma.Web.Plugs.HTTPSecurityPlug.warn_if_disabled()
     Pleroma.ApplicationRequirements.verify!()
-    setup_instrumenters()
     load_custom_modules()
     Pleroma.Docs.JSON.compile()
     limiters_setup()
@@ -91,6 +90,7 @@ defmodule Pleroma.Application do
     # Define workers and child supervisors to be supervised
     children =
       [
+        Pleroma.PromEx,
         Pleroma.Repo,
         Config.TransferTask,
         Pleroma.Emoji,
@@ -170,29 +170,6 @@ defmodule Pleroma.Application do
     end
   end
 
-  defp setup_instrumenters do
-    require Prometheus.Registry
-
-    if Application.get_env(:prometheus, Pleroma.Repo.Instrumenter) do
-      :ok =
-        :telemetry.attach(
-          "prometheus-ecto",
-          [:pleroma, :repo, :query],
-          &Pleroma.Repo.Instrumenter.handle_event/4,
-          %{}
-        )
-
-      Pleroma.Repo.Instrumenter.setup()
-    end
-
-    Pleroma.Web.Endpoint.MetricsExporter.setup()
-    Pleroma.Web.Endpoint.PipelineInstrumenter.setup()
-
-    # Note: disabled until prometheus-phx is integrated into prometheus-phoenix:
-    # Pleroma.Web.Endpoint.Instrumenter.setup()
-    PrometheusPhx.setup()
-  end
-
   defp cachex_children do
     [
       build_cachex("used_captcha", ttl_interval: seconds_valid_interval()),