Provide metrics on root URL

lib/kafkaex_lag_exporter_web/endpoint.ex

@@ -0,0 +1,45 @@
+defmodule KafkaexLagExporterWeb.Endpoint do
+  use Phoenix.Endpoint, otp_app: :kafkaex_lag_exporter
+
+  plug PromEx.Plug, path: "/", prom_ex_module: KafkaexLagExporter.PromEx
+
+  # The session will be stored in the cookie and signed,
+  # this means its contents can be read but not tampered with.
+  # Set :encryption_salt if you would also like to encrypt it.
+  @session_options [
+    store: :cookie,
+    key: "_kafkaex_lag_exporter_key",
+    signing_salt: "f/R6/xEO"
+  ]
+
+  # socket "/live", Phoenix.LiveView.Socket, websocket: [connect_info: [session: @session_options]]
+
+  # Serve at "/" the static files from "priv/static" directory.
+  #
+  # You should set gzip to true if you are running phx.digest
+  # when deploying your static files in production.
+  plug Plug.Static,
+    at: "/",
+    from: :kafkaex_lag_exporter,
+    gzip: false,
+    only: ~w(assets fonts images favicon.ico robots.txt)
+
+  # Code reloading can be explicitly enabled under the
+  # :code_reloader configuration of your endpoint.
+  if code_reloading? do
+    plug Phoenix.CodeReloader
+  end
+
+  plug Plug.RequestId
+  plug Plug.Telemetry, event_prefix: [:phoenix, :endpoint]
+
+  plug Plug.Parsers,
+    parsers: [:urlencoded, :multipart, :json],
+    pass: ["*/*"],
+    json_decoder: Phoenix.json_library()
+
+  plug Plug.MethodOverride
+  plug Plug.Head
+  plug Plug.Session, @session_options
+  plug KafkaexLagExporterWeb.Router
+end

lib/kafkaex_lag_exporter_web/router.ex

@@ -0,0 +1,11 @@
+defmodule KafkaexLagExporterWeb.Router do
+  use KafkaexLagExporterWeb, :router
+
+  pipeline :api do
+    plug :accepts, ["json"]
+  end
+
+  scope "/api", KafkaexLagExporterWeb do
+    pipe_through :api
+  end
+end

lib/kafkaex_lag_exporter_web/telemetry.ex

@@ -0,0 +1,50 @@
+defmodule KafkaexLagExporterWeb.Telemetry do
+  @moduledoc false
+
+  use Supervisor
+  import Telemetry.Metrics
+
+  def start_link(arg) do
+    Supervisor.start_link(__MODULE__, arg, name: __MODULE__)
+  end
+
+  @impl true
+  def init(_arg) do
+    children = [
+      # Telemetry poller will execute the given period measurements
+      # every 10_000ms. Learn more here: https://hexdocs.pm/telemetry_metrics
+      {:telemetry_poller, measurements: periodic_measurements(), period: 10_000}
+      # Add reporters as children of your supervision tree.
+      # {Telemetry.Metrics.ConsoleReporter, metrics: metrics()}
+    ]
+
+    Supervisor.init(children, strategy: :one_for_one)
+  end
+
+  def metrics do
+    [
+      # Phoenix Metrics
+      summary("phoenix.endpoint.stop.duration",
+        unit: {:native, :millisecond}
+      ),
+      summary("phoenix.router_dispatch.stop.duration",
+        tags: [:route],
+        unit: {:native, :millisecond}
+      ),
+
+      # VM Metrics
+      summary("vm.memory.total", unit: {:byte, :kilobyte}),
+      summary("vm.total_run_queue_lengths.total"),
+      summary("vm.total_run_queue_lengths.cpu"),
+      summary("vm.total_run_queue_lengths.io")
+    ]
+  end
+
+  defp periodic_measurements do
+    [
+      # A module, function and arguments to be invoked periodically.
+      # This function must call :telemetry.execute/3 and a metric must be added above.
+      # {KafkaexLagExporterWeb, :count_users, []}
+    ]
+  end
+end

lib/kafkaex_lag_exporter_web/views/error_helpers.ex

@@ -0,0 +1,16 @@
+defmodule KafkaexLagExporterWeb.ErrorHelpers do
+  @moduledoc """
+  Conveniences for translating and building error messages.
+  """
+
+  @doc """
+  Translates an error message.
+  """
+  def translate_error({msg, opts}) do
+    # Because the error messages we show in our forms and APIs
+    # are defined inside Ecto, we need to translate them dynamically.
+    Enum.reduce(opts, msg, fn {key, value}, acc ->
+      String.replace(acc, "%{#{key}}", fn _ -> to_string(value) end)
+    end)
+  end
+end

lib/kafkaex_lag_exporter_web/views/error_view.ex

@@ -0,0 +1,16 @@
+defmodule KafkaexLagExporterWeb.ErrorView do
+  use KafkaexLagExporterWeb, :view
+
+  # If you want to customize a particular status code
+  # for a certain format, you may uncomment below.
+  # def render("500.json", _assigns) do
+  #   %{errors: %{detail: "Internal Server Error"}}
+  # end
+
+  # By default, Phoenix returns the status message from
+  # the template name. For example, "404.json" becomes
+  # "Not Found".
+  def template_not_found(template, _assigns) do
+    %{errors: %{detail: Phoenix.Controller.status_message_from_template(template)}}
+  end
+end