[Enhancement] Add Prometheus support (#556)

* Added prometheus to deps list

* WIP - screwing around with Prometheus and grafana

* Added basic prometheus config

* Updated docs in prom_ex module

* Updated README

lib/pinchflat/application.ex

@@ -11,6 +11,7 @@ defmodule Pinchflat.Application do
     check_and_update_timezone()
 
     children = [
+      Pinchflat.PromEx,
       PinchflatWeb.Telemetry,
       Pinchflat.Repo,
       # Must be before startup tasks

lib/pinchflat/prom_ex.ex

@@ -0,0 +1,40 @@
+defmodule Pinchflat.PromEx do
+  @moduledoc """
+  Configuration for the PromEx library which provides Prometheus metrics
+  """
+
+  use PromEx, otp_app: :pinchflat
+
+  alias PromEx.Plugins
+
+  @impl true
+  def plugins do
+    [
+      Plugins.Application,
+      Plugins.Beam,
+      {Plugins.Phoenix, router: PinchflatWeb.Router, endpoint: PinchflatWeb.Endpoint},
+      Plugins.Ecto,
+      Plugins.Oban,
+      Plugins.PhoenixLiveView
+    ]
+  end
+
+  @impl true
+  def dashboard_assigns do
+    [
+      default_selected_interval: "30s"
+    ]
+  end
+
+  @impl true
+  def dashboards do
+    [
+      {:prom_ex, "application.json"},
+      {:prom_ex, "beam.json"},
+      {:prom_ex, "phoenix.json"},
+      {:prom_ex, "ecto.json"},
+      {:prom_ex, "oban.json"},
+      {:prom_ex, "phoenix_live_view.json"}
+    ]
+  end
+end

lib/pinchflat_web/endpoint.ex

@@ -32,6 +32,8 @@ defmodule PinchflatWeb.Endpoint do
     plug Phoenix.Ecto.CheckRepoStatus, otp_app: :pinchflat
   end
 
+  plug PromEx.Plug, prom_ex_module: Pinchflat.PromEx
+
   plug Phoenix.LiveDashboard.RequestLogger,
     param_key: "request_logger",
     cookie_key: "request_logger"