monitor.ex

# lib/monitor.ex
defmodule MyApp.Monitor do

  def health_check do
      ExStatsD.histogram(get_concache_mem_size(:css_cache), "css.cache.memory", ["css_cache_memory"])
      ExStatsD.histogram(get_concache_mem_size(:sass_cache), "sass.cache.memory", ["sass_cache_memory"])
      ExStatsD.histogram(ConCache.size(:css_cache), "css.cache.size", ["css_cache_size"])
      ExStatsD.histogram(ConCache.size(:sass_cache), "sass.cache.size", ["sass_cache_size"])
      ExStatsD.histogram(:erlang.memory(:ets), "erlang.ets.memory", ["ets_size"])
      ExStatsD.histogram(:erlang.memory |> Keyword.get(:total), "erlang.memory.memory", ["ets_size"])
  end

  defp get_concache_mem_size(name) do
    name |> ConCache.ets |> :ets.info |> Keyword.get(:memory) |> (fn(x) -> x * :erlang.system_info(:wordsize) end).()
  end
end

prod.ex

# config/prod.ex
config :quantum, cron: [
  # Every minute
  "* * * * *": {MyApp.Monitor, :health_check}
]

config :ex_statsd,
  host: "localhost",
  port: 8125,
  namespace: "MyApp"

request_status_plug.ex

# web/plugs/request_status_plug.ex
defmodule MyApp.RequestStatusPlug do
  @behaviour Plug
  import Plug.Conn, only: [register_before_send: 2]

  def init(opts), do: opts

  def call(conn, _config) do
    req_start_time = :os.timestamp

    register_before_send conn, fn conn ->
      # increment count
      ExStatsD.increment("response.count")

      # log response time in microseconds
      req_end_time = :os.timestamp
      duration = :timer.now_diff(req_end_time, req_start_time)
      ExStatsD.timer(duration, "response.time")

      conn
    end
  end
end