Use start-stop-daemon to launch/exit node app.

app.js

#!/usr/bin/env node
//app.js

var http = require('http');

server = http.createServer(function(req, res){
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.write('<h1>Node.js</h1>');
    res.end('<p>Hello World</p>');
}).listen(process.env.PORT||4321);
console.log("HTTP server is listening at port "+server.address().port);

start.sh

#!/usr/bin/env bash
start-stop-daemon --start --quiet --pidfile $1 -m --exec /usr/bin/env -- node app.js > $2 &

stop.sh

#/usr/bin/env bash
start-stop-daemon --stop -p $1