Adding a Node.js application as a service on your Ubuntu server is pretty easy using Ubuntu's Upstart. Just create a config file at /etc/init/myapp.conf with the following:
description "Your app name here"
author "This would be you"
# Start the service after everything loaded
start on (local-filesystems and net-device-up IFACE=eth0)
stop on shutdown
# Automatically restart service
respawn limit 99 5
# Navigate to your app directory