node.js as a system web service with upstart

app.conf

description "app"
start on filesystem
stop on runlevel S
respawn

env PORT=3002
env APP_USER=app
# @TODO: put NODE_ENV here
env NODE_PATH=/usr/local/lib/node_modules

exec /usr/local/bin/node /var/www/run.js >> /var/log/app.log 2>&1

app.js

var express = require('express');
var app = express.createServer();

app.get("/", function(req, res, next) {
  res.send("Hello World\n");
});

exports = module.exports = app;

run.js

var app = require('./app');
app.listen(process.env.PORT || 3000, function() {
  if (process.getuid() === 0) {
    process.setgid(process.env.APP_USER || 'www-data');
    process.setuid(process.env.APP_GROUP || process.env.APP_USER || 'www-data');
  }
});