Node.js cluster support on Heroku — freaking sweet!

app.js

var cluster = require('cluster');
var http = require('http');
var numCPUs = require('os').cpus().length;
var pid = process.pid;
var port = process.env['PORT'] || 8000;

if (cluster.isMaster) {
  console.log('Master:', pid);

  // Fork workers -- one less than the number of CPUs.
  for (var i = 1; i < numCPUs; i++) {
    cluster.fork();
  }

  cluster.on('death', function(worker) {
    console.error('DEATH:', worker.pid);
  });
} else {
  console.log('Worker:', pid);

  // Worker processes have a http server.
  http.createServer(function(req, res) {
    console.log('Request:', pid);
    res.writeHead(200);
    res.end("Hello world! (From process " + pid + ".)\n");
  }).listen(port);
}

I'd recommend using https://github.com/brianc/node-forky now instead of this.