feat: expose system metrics (#4)

Use prom_ex to expose system metrics to prometheus and create dashboards.

Co-authored-by: Joao P Dubas <joao.dubas@gmail.com>
Reviewed-on: #4

lib/wabanex/application.ex

@@ -7,6 +7,8 @@ defmodule Wabanex.Application do
 
   def start(_type, _args) do
     children = [
+      # Start the PromEx supervisor
+      Wabanex.PromEx,
       # Start the Ecto repository
       Wabanex.Repo,
       # Start the Telemetry supervisor

lib/wabanex/prom_ex.ex

@@ -0,0 +1,102 @@
+defmodule Wabanex.PromEx do
+  @moduledoc """
+  Be sure to add the following to finish setting up PromEx:
+
+  1. Update your configuration (config.exs, dev.exs, prod.exs, releases.exs, etc) to
+     configure the necessary bit of PromEx. Be sure to check out `PromEx.Config` for
+     more details regarding configuring PromEx:
+     ```
+     config :wabanex, Wabanex.PromEx,
+       disabled: false,
+       manual_metrics_start_delay: :no_delay,
+       drop_metrics_groups: [],
+       grafana: :disabled,
+       metrics_server: :disabled
+     ```
+
+  2. Add this module to your application supervision tree. It should be one of the first
+     things that is started so that no Telemetry events are missed. For example, if PromEx
+     is started after your Repo module, you will miss Ecto's init events and the dashboards
+     will be missing some data points:
+     ```
+     def start(_type, _args) do
+       children = [
+         Wabanex.PromEx,
+
+         ...
+       ]
+
+       ...
+     end
+     ```
+
+  3. Update your `endpoint.ex` file to expose your metrics (or configure a standalone
+     server using the `:metrics_server` config options). Be sure to put this plug before
+     your `Plug.Telemetry` entry so that you can avoid having calls to your `/metrics`
+     endpoint create their own metrics and logs which can pollute your logs/metrics given
+     that Prometheus will scrape at a regular interval and that can get noisy:
+     ```
+     defmodule WabanexWeb.Endpoint do
+       use Phoenix.Endpoint, otp_app: :wabanex
+
+       ...
+
+       plug PromEx.Plug, prom_ex_module: Wabanex.PromEx
+
+       ...
+     end
+     ```
+
+  4. Update the list of plugins in the `plugins/0` function return list to reflect your
+     application's dependencies. Also update the list of dashboards that are to be uploaded
+     to Grafana in the `dashboards/0` function.
+  """
+
+  use PromEx, otp_app: :wabanex
+
+  alias PromEx.Plugins
+
+  @impl true
+  def plugins do
+    [
+      # PromEx built in plugins
+      Plugins.Application,
+      Plugins.Beam,
+      # {Plugins.Phoenix, router: WabanexWeb.Router, endpoint: WabanexWeb.Endpoint},
+      Plugins.Ecto,
+      # Plugins.Oban,
+      # Plugins.PhoenixLiveView,
+      Plugins.Absinthe
+      # Plugins.Broadway,
+
+      # Add your own PromEx metrics plugins
+      # Wabanex.Users.PromExPlugin
+    ]
+  end
+
+  @impl true
+  def dashboard_assigns do
+    [
+      datasource_id: "prometheus",
+      default_selected_interval: "30s"
+    ]
+  end
+
+  @impl true
+  def dashboards do
+    [
+      # PromEx built in Grafana dashboards
+      {: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"},
+      {:prom_ex, "absinthe.json"}
+      # {:prom_ex, "broadway.json"},
+
+      # Add your dashboard definitions here with the format: {:otp_app, "path_in_priv"}
+      # {:wabanex, "/grafana_dashboards/user_metrics.json"}
+    ]
+  end
+end

lib/wabanex_web/endpoint.ex

@@ -16,6 +16,8 @@ defmodule WabanexWeb.Endpoint do
 
   socket "/live", Phoenix.LiveView.Socket, websocket: [connect_info: [session: @session_options]]
 
+  plug PromEx.Plug, prom_ex_module: Wabanex.PromEx
+
   # Serve at "/" the static files from "priv/static" directory.
   #
   # You should set gzip to true if you are running phx.digest

lib/wabanex_web/schema/types/custom/date_range.ex

@@ -17,10 +17,11 @@ defmodule WabanexWeb.Schema.Types.Custom.DateRange do
   end
 
   @spec serialize_range(PgRanges.DateRange.t()) :: String.t()
-  @spec serialize_range(list(DateTime.t() | nil)) :: String.t()
+  @spec serialize_range(list(DateTime.t() | nil | atom)) :: String.t()
   defp serialize_range(%PgRanges.DateRange{lower: start_range, upper: end_range}),
     do: serialize_range([start_range, end_range])
 
+  defp serialize_range([start_range, :unbound]), do: serialize_range([start_range, nil])
   defp serialize_range([start_range, nil]), do: "#{Date.to_iso8601(start_range)},"
 
   defp serialize_range([start_range, end_range]),