Add basic metrics

lib/wiki/application.ex

@@ -14,9 +14,11 @@ defmodule Wiki.Application do
       # Start the PubSub system
       {Phoenix.PubSub, name: Wiki.PubSub},
       # Start the Endpoint (http/https)
-      WikiWeb.Endpoint
+      WikiWeb.Endpoint,
       # Start a worker by calling: Wiki.Worker.start_link(arg)
       # {Wiki.Worker, arg}
+      {Wiki.MetricStorage, WikiWeb.Telemetry.metrics()},
+      Wiki.MetricGenerator
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html

lib/wiki/metric_generator.ex

@@ -0,0 +1,34 @@
+defmodule Wiki.MetricGenerator do
+  use GenServer
+  alias Wiki.Repo
+  alias Wiki.Content.{Page, PageLink, Upload}
+
+  def start_link(state) do
+    GenServer.start_link(__MODULE__, state, name: __MODULE__)
+  end
+
+  @impl true
+  def init(state) do
+    update_metrics()
+
+    # 5 minutes
+    Process.send_after(self(), :update, 5 * 60 * 1000)
+
+    {:ok, state}
+  end
+
+  @impl true
+  def handle_info(:update, state) do
+    update_metrics()
+    {:noreply, state}
+  end
+
+  def update_metrics do
+    pages = Repo.aggregate(Page, :count)
+    uploads = Repo.aggregate(Upload, :count)
+    links = Repo.aggregate(PageLink, :count)
+    :telemetry.execute([:wiki, :pages], %{count: pages})
+    :telemetry.execute([:wiki, :uploads], %{count: uploads})
+    :telemetry.execute([:wiki, :links], %{count: links})
+  end
+end

lib/wiki/metric_storage.ex

@@ -0,0 +1,66 @@
+defmodule Wiki.MetricStorage do
+  use GenServer
+
+  @history_buffer_size 50
+
+  def metrics_history(metric) do
+    GenServer.call(__MODULE__, {:data, metric})
+  end
+
+  def start_link(args) do
+    GenServer.start_link(__MODULE__, args, name: __MODULE__)
+  end
+
+  @impl true
+  def init(metrics) do
+    Process.flag(:trap_exit, true)
+
+    metric_histories_map =
+      metrics
+      |> Enum.map(fn metric ->
+        attach_handler(metric)
+        {metric, CircularBuffer.new(@history_buffer_size)}
+      end)
+      |> Map.new()
+
+    {:ok, metric_histories_map}
+  end
+
+  @impl true
+  def terminate(_, metrics) do
+    for metric <- metrics do
+      :telemetry.detach({__MODULE__, metric, self()})
+    end
+
+    :ok
+  end
+
+  defp attach_handler(%{event_name: name_list} = metric) do
+    :telemetry.attach(
+      {__MODULE__, metric, self()},
+      name_list,
+      &__MODULE__.handle_event/4,
+      metric
+    )
+  end
+
+  def handle_event(_event_name, data, metadata, metric) do
+    if data = Phoenix.LiveDashboard.extract_datapoint_for_metric(metric, data, metadata) do
+      GenServer.cast(__MODULE__, {:telemetry_metric, data, metric})
+    end
+  end
+
+  @impl true
+  def handle_cast({:telemetry_metric, data, metric}, state) do
+    {:noreply, update_in(state[metric], &CircularBuffer.insert(&1, data))}
+  end
+
+  @impl true
+  def handle_call({:data, metric}, _from, state) do
+    if history = state[metric] do
+      {:reply, CircularBuffer.to_list(history), state}
+    else
+      {:reply, [], state}
+    end
+  end
+end

lib/wiki_web/router.ex

@@ -56,7 +56,9 @@ defmodule WikiWeb.Router do
   scope "/", WikiWeb do
     pipe_through [:browser, :require_authenticated_user, :require_admin_user]
 
-    live_dashboard "/dashboard", metrics: WikiWeb.Telemetry
+    live_dashboard "/dashboard",
+      metrics: WikiWeb.Telemetry,
+      metrics_history: {Wiki.MetricStorage, :metrics_history, []}
   end
 
   scope "/", WikiWeb do

lib/wiki_web/telemetry.ex

@@ -21,6 +21,11 @@ defmodule WikiWeb.Telemetry do
 
   def metrics do
     [
+      # Wiki Metrics
+      last_value("wiki.pages.count"),
+      last_value("wiki.uploads.count"),
+      last_value("wiki.links.count"),
+
       # Phoenix Metrics
       summary("phoenix.endpoint.stop.duration",
         unit: {:native, :millisecond}

mix.exs

@@ -47,7 +47,8 @@ defmodule Wiki.MixProject do
       {:jason, "~> 1.0"},
       {:plug_cowboy, "~> 2.0"},
       {:phx_gen_auth, "~> 0.4.0", only: :dev, runtime: false},
-      {:earmark, "~> 1.4.10"}
+      {:earmark, "~> 1.4.10"},
+      {:circular_buffer, "~> 0.3.0"}
     ]
   end
 

mix.lock

@@ -1,6 +1,7 @@
 %{
   "argon2_elixir": {:hex, :argon2_elixir, "2.3.0", "e251bdafd69308e8c1263e111600e6d68bd44f23d2cccbe43fcb1a417a76bc8e", [:make, :mix], [{:comeonin, "~> 5.3", [hex: :comeonin, repo: "hexpm", optional: false]}, {:elixir_make, "~> 0.6", [hex: :elixir_make, repo: "hexpm", optional: false]}], "hexpm", "28ccb63bff213aecec1f7f3dde9648418b031f822499973281d8f494b9d5a3b3"},
   "bcrypt_elixir": {:hex, :bcrypt_elixir, "2.2.0", "3df902b81ce7fa8867a2ae30d20a1da6877a2c056bfb116fd0bc8a5f0190cea4", [:make, :mix], [{:comeonin, "~> 5.3", [hex: :comeonin, repo: "hexpm", optional: false]}, {:elixir_make, "~> 0.6", [hex: :elixir_make, repo: "hexpm", optional: false]}], "hexpm", "762be3fcb779f08207531bc6612cca480a338e4b4357abb49f5ce00240a77d1e"},
+  "circular_buffer": {:hex, :circular_buffer, "0.3.0", "3eaa7e349ab07cff53dd1c25eb179ac14913fe1e407762260402a291dac4af96", [:mix], [], "hexpm", "f582b2ce394f8965cadf43c5b140f399b83dc8404aef701cb41c928c4bac1943"},
   "comeonin": {:hex, :comeonin, "5.3.1", "7fe612b739c78c9c1a75186ef2d322ce4d25032d119823269d0aa1e2f1e20025", [:mix], [], "hexpm", "d6222483060c17f0977fad1b7401ef0c5863c985a64352755f366aee3799c245"},
   "connection": {:hex, :connection, "1.0.4", "a1cae72211f0eef17705aaededacac3eb30e6625b04a6117c1b2db6ace7d5976", [:mix], [], "hexpm", "4a0850c9be22a43af9920a71ab17c051f5f7d45c209e40269a1938832510e4d9"},
   "cowboy": {:hex, :cowboy, "2.8.0", "f3dc62e35797ecd9ac1b50db74611193c29815401e53bac9a5c0577bd7bc667d", [:rebar3], [{:cowlib, "~> 2.9.1", [hex: :cowlib, repo: "hexpm", optional: false]}, {:ranch, "~> 1.7.1", [hex: :ranch, repo: "hexpm", optional: false]}], "hexpm", "4643e4fba74ac96d4d152c75803de6fad0b3fa5df354c71afdd6cbeeb15fac8a"},