API heartbeat take around 100ms to reply

I created an API to check if my server is alive, after checking the log I saw my reply take >= 100s from the server but on my computer, it takes about 8ms… Can someone tell me why?

Log

14:06:29.154 request_id=XXX [info] GET /api/heartbeat
14:06:29.154 request_id=XXX [info] Sent 200 in 306s
14:06:34.155 request_id=XXX [info] GET /api/heartbeat
14:06:34.155 request_id=XXX [info] Sent 200 in 86s
14:06:39.153 request_id=XXX [info] GET /api/heartbeat
14:06:39.153 request_id=XXX [info] Sent 200 in 112s

API

def api_heartbeat(conn, _params) do
    send_resp(conn, :ok, "")
end

Route

pipeline :api do
    plug :accepts, ["json"]
  end

scope "/api", PhoenixTWeb do
    pipe_through :api

    get "/heartbeat", PageController, :api_heartbeat
end

mix.exs

defmodule PhoenixT.MixProject do
  use Mix.Project

  def project do
    [
      app: :phoenix_t,
      version: "1.1.0",
      elixir: "1.8.2",
      elixirc_paths: elixirc_paths(Mix.env()),
      compilers: [:phoenix, :gettext] ++ Mix.compilers(),
      start_permanent: Mix.env() == :prod,
      deps: deps(),
      test_coverage: [tool: ExCoveralls],
      preferred_cli_env: [coveralls: :test, "coveralls.detail": :test, "coveralls.post": :test, "coveralls.html": :test]
    ]
  end

  # Configuration for the OTP application.
  #
  # Type `mix help compile.app` for more information.
  def application do
    [
      mod: {PhoenixT.Application, []},
      extra_applications: [:logger, :runtime_tools, :peerage]
    ]
  end

  # Specifies which paths to compile per environment.
  defp elixirc_paths(:test), do: ["lib", "test/support"]
  defp elixirc_paths(_), do: ["lib"]

  # Specifies your project dependencies.
  #
  # Type `mix help deps` for examples and options.
  defp deps do
    [
      {:phoenix, "~> 1.4.6"},
      {:phoenix_pubsub, "~> 1.1"},
      {:phoenix_html, "~> 2.11"},
      {:phoenix_live_reload, "~> 1.2", only: :dev},
      {:gettext, "~> 0.11"},
      {:jason, "~> 1.0"},
      {:plug_cowboy, "~> 2.0"},
      {:excoveralls, "~> 0.10", only: :test},
      {:distillery, "~> 2.0", override: true},
      {:peerage, "~> 1.0"},
    ]
  end
end

conf.exs

use Mix.Config

# Configures the endpoint
config :phoenix_t, PhoenixTWeb.Endpoint,
  url: [host: "localhost"],
  secret_key_base: "secret_key_base",
  render_errors: [view: PhoenixTWeb.ErrorView, accepts: ~w(html json)],
  pubsub: [name: PhoenixT.PubSub, adapter: Phoenix.PubSub.PG2]

# Configures Elixir's Logger
config :logger, :console,
  format: "$time $metadata[$level] $message\n",
  metadata: [:request_id]

# Use Jason for JSON parsing in Phoenix
config :phoenix, :json_library, Jason

# Import environment specific config. This must remain at the bottom
# of this file so it overrides the configuration defined above.
import_config "#{Mix.env()}.exs"

prod.exs

config :phoenix_t, PhoenixTWeb.Endpoint,
  http: [:inet6, port: "${PORT}"],
  url: [host: "${HOST}", port: "${PORT}"], # This is critical for ensuring web-sockets properly authorize.
  cache_static_manifest: "priv/static/cache_manifest.json",
  server: true,
  secret_key_base: "secret_key_base",
  root: ".",
  # TODO - Need to remove the ligne below
  check_origin: false,
  version: Application.spec(:phoenix_t, :vsn)

# Do not print debug messages in production
config :logger, level: :info