Basic node 0.6.x cluster skeleton

app.js

var http = require('http');

var app = module.exports = http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.end();
});

server.js

// Require the modules
var cluster = require('cluster'),
    fs = require('fs'),
    path = require('path');

// Production flag
var isProduction = process.env.NODE_ENV == 'production';

/* CLUSTER */

// Current PID path (expects a directory under root named pids)
var PIDS = path.join(__dirname, 'pids');

// Clear all PIDs
function clearPids() {
  var filenames = fs.readdirSync(PIDS);
  for (var i = 0, len = filenames.length; i < len; ++i) {
    var filename = filenames[i];
    if (path.extname(filename) == '.pid') clearPid(filename);
  }
};

// Clear PID
function clearPid(pid) {
  fs.unlinkSync(path.join(PIDS, pid));
};

// Write the current PID
function writePid() {
  // Write the current PID
  var filename = path.join(PIDS, cluster.isMaster ? 'master.pid' : 'worker.' + process.pid + '.pid');
  fs.writeFileSync(filename, process.pid, 'utf8');
};

// Gracefully kill workers by sending a SIGQUIT
function killWorkers() {
  // Read the files in the pids folder
  var filenames = fs.readdirSync(PIDS);
  for (var i = 0, len = filenames.length; i < len; ++i) {
    var filename = filenames[i];
    if (filename.substring(0, 7) == 'worker.' && path.extname(filename) == '.pid') {
      // READ the PID and send a SIGQUIT
      var pid = fs.readFileSync(path.join(PIDS, filename));
      if (pid && pid != '') process.kill(pid, 'SIGQUIT');
    }
  }
};

/* APPLICATION LOGIC */

// Check if master or worker
if (isProduction && cluster.isMaster) {

  // Clear all PIDs
  clearPids();

  // Write the current PID
  writePid();

  // Register restart handler
  process.on('SIGUSR2', killWorkers);

  // Reload worker on death
  cluster.on('death', function(worker) {
    console.log('Worker ' + worker.pid + ' died... restarting');
    // Clear the PID file
    clearPid('worker.' + worker.pid + '.pid');
    cluster.fork();
  });

  // Create a workers per CPU
  for (var i = 0, count = require('os').cpus().length; i < count; ++i) {
    cluster.fork();    
  }

} else {

  if (isProduction) {
    // Write the current PID
    writePid();
    console.log('Worker ' + process.pid + ' started');
  } else {
    clearPids();
  }

  // Create the application
  var app = require('./app');

  if (isProduction) {
    // Register restart handler
    process.once('SIGQUIT', function() {
      // Shutdown your application here
      app.close()
      process.exit();
    });
  }

  // Start the server
  app.listen(8000);
  console.log("HTTP server listening on port %d", 8000);

}

The master and worker processes write their PID to a file in a directory under root named pids. This expects that the directory exists and is writable.

The master handles SIGUSR2 as a graceful restart, by dispatching a SIGQUIT to all workers, which executes the callback on line 82.

Running node server.js will spin up the application as a single process not using cluster. Running NODE_ENV=production node server.js will us cluster and create one worker per CPU core.