A GenServer implementation that starts a Node.js server process using Elixir ports.

server.ex

defmodule NodeProcess.Server do
  @moduledoc """
  A GenServer implementation that starts a Node.js server process using Elixir ports.
  """

  # Elixir automatically defines callbacks not overriden
  use GenServer

  @doc """
  Called when application started via application.ex.
  """
  def start_link(initial_value) do
    GenServer.start_link(__MODULE__, initial_value, name: __MODULE__)
  end

  @doc """
  Port spawns executable to run node server process via wrapper shell script.

  An `enoent` error means FileName specified in {spawn_executable, FileName}
  does not point out an existing file.

  Docs for Port here: https://hexdocs.pm/elixir/Port.html

  Docs for open_port options here: http://erlang.org/doc/man/erlang.html#open_port-2
  """
  def init(:ok) do
    {:ok, %{port: start_port()}}
  end

  @doc """
  Close port when the genserver is about to exit.
  """
  def terminate(_reason, %{port: port}) do
    Port.close(port)
  end

  defp start_port do
    js_file = "#{__DIR__}/../../../../../your-node-app/index.js"

    # Elixir documentation recommends use of wrapper script
    # to prevent zombie processes.
    # See: https://hexdocs.pm/elixir/Port.html#module-zombie-processes
    process_wrapper = "#{__DIR__}/../../wrapper.sh"

    Port.open({:spawn_executable, process_wrapper}, [
      {:args, ["node", js_file]}
    ])
  end
end