elixir startup script with graceful shutdown

example_server.ex

defmodule Example.Server do
  use GenServer

  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, :ok, opts)
  end

  def init(state) do
    Process.flag(:trap_exit, true) # must trap exit for terminate call back to work
    IO.inspect "Starting server..."

    {:ok, state}
  end

  def terminate(reason, state) do
    IO.inspect "Going Down: #{inspect(state)}"
    IO.inspect reason
    :normal
  end
end

start.sh

#!/bin/bash

HOSTNAME="localhost"
PORT=${PORT-4000}
NODE="app_$PORT"

if [ -z "$COOKIE" ]
then
  COOKIE=$(cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 | head -n 1)
fi

# Default to 64 threads
if [ -z "$THREAD_COUNT" ]
then
   THREAD_COUNT="64"
fi

stop(){
  echo Shutting down server
  erl \
    -sname "shutdown" \
    -setcookie $COOKIE \
    -noinput \
    -eval "rpc:call('$NODE', init, stop, []), init:stop()."
}
trap stop SIGQUIT SIGINT SIGTERM

exec elixir \
  -pa _build/prod/consolidated \
  --no-halt \
  --erl "+A$THREAD_COUNT" \
  --erl "+K true" \
  --erl "-smp auto" \
  --erl "+scl false" \
  --erl "+spp true" \
  --erl "+swt low" \
  --erl "+sbwt long" \
  --sname $NODE \
  --cookie $COOKIE \
  -S mix run \
    --no-compile \
    $@ \
  &

pid=$!
sleep 0

while kill -0 $pid 2>/dev/null ; do wait $pid ; done