Add minimal configuration system

config/config.exs

@@ -0,0 +1,6 @@
+import Config
+
+config :ha_handler,
+	http_port: 4000,
+	haproxy_socket: System.get_env("HAPROXY_SOCKET") || "/var/run/haproxy.sock"
+

lib/ha_handler.ex

@@ -1,18 +1,6 @@
 defmodule HAHandler do
-  @moduledoc """
-  Documentation for `HAHandler`.
-  """
+  @moduledoc false
 
-  @doc """
-  Hello world.
-
-  ## Examples
-
-      iex> HAHandler.hello()
-      :world
-
-  """
-  def hello do
-    :world
-  end
+  def http_port, do: Application.get_env(:ha_handler, :http_port)
+  def haproxy_socket, do: Application.get_env(:ha_handler, :haproxy_socket)
 end

lib/ha_handler/application.ex

@@ -5,10 +5,12 @@ defmodule HAHandler.Application do
 
   use Application
 
+  import HAHandler
+
   @impl true
   def start(_type, _args) do
     children = [
-      {Plug.Cowboy, scheme: :http, plug: HAHandler.Web, options: [port: 4000]}
+      {Plug.Cowboy, scheme: :http, plug: HAHandler.Web, options: [port: http_port()]}
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html