Problem with cluster in Node.js (Express)

app.js

var cluster = require('cluster');

function fibonacci(n) {
	if (n < 2) {
		return 1;
	} else {
		return fibonacci(n - 2) + fibonacci(n - 1);
	}
}

if (cluster.isMaster) {
	for (var i = 0; i < require('os').cpus().length; i += 1) {
		cluster.fork();
	}
} else {
	var app = require('express')();

	app.get('/slow', function(req, res) {
		fibonacci(43);
		res.set('x-pid', cluster.worker.id + ' pid=' + process.pid);
		res.send('SLOW: worker ' + cluster.worker.id + ' pid=' + process.pid + '<img src="a"><img src="b"><img src="c"><img src="d"><img src="e">');
	});

	app.get('/fast', function(req, res) {
		res.set('x-pid', cluster.worker.id + ' pid=' + process.pid);
		res.send('FAST: worker ' + cluster.worker.id + ' pid=' + process.pid + '<img src="a"><img src="b"><img src="c"><img src="d"><img src="e">');
	});

	app.get(/^\/\w$/, function(req, res) {
		res.set('x-pid', cluster.worker.id + ' pid=' + process.pid);
		res.send('');
	});

	app.listen(8080);
}