Simple elixir web server with plug

Simple elixir web server with plug

Everybody seems to use Phoenix for their web applications in Elixir. Sometimes,
however, you simply would like to take the easy route and write a small server
at a lower lever because you don’t need all the functionality provided by
Phoenix. It is a layer on top of erlang server Cowboy.
You can find the final app here at github: simple_plug.

Let’s start. First, create a new mix application with a supervisor:

mix new simple_plug --sup

Then add the plug and cowboy dependency into the mix.exs file:

defp deps do
     {:cowboy, "~> 1.0.0"},
     {:plug, "~> 0.12"},

Run mix do deps.get, compile to get and compile the dependencies.

We then need a starter for the plug server lib/plug_starter.ex:

defmodule SimplePlug.Plugstarter do

  def start_link() do
    {:ok, _} = Plug.Adapters.Cowboy.http SimplePlug.Router, []


which is started through our supervisor at lib/simple_plug.ex:

defmodule SimplePlug do
  use Application

  # See
  # for more information on OTP Applications
  def start(_type, _args) do
    import Supervisor.Spec, warn: false

    children = [
      # Define workers and child supervisors to be supervised
      # worker(SimplePlug.Worker, [arg1, arg2, arg3])
      worker(SimplePlug.Plugstarter, [])

    # See
    # for other strategies and supported options
    opts = [strategy: :one_for_one, name: SimplePlug.Supervisor]
    Supervisor.start_link(children, opts)

The last thing we need it the plug-router, which responds to the http request.
In our case we simply show back the entered parameters. If you enter
http://localhost:4000/?aaa=1234 it would return received %{"aaa" => "1234"}.
If you use any other route, it returns a 404 page.
Paste the following code into lib/router.ex:

defmodule SimplePlug.Router do
  use Plug.Router
  require Logger

  # plug Plug.Logger
  plug :match
  plug :dispatch

  def init(options) do
    # initialize your options here


  get "/" do
    # Get the parameters
    conn = fetch_query_params(conn)

    send_resp(conn, 200, "received #{inspect(conn.params)}")

  match _ do
    send_resp(conn, 404, "oops")


Now you can start the server with iex -S mix and enjoy your lovely plug server at