A naïve way to broadcast a message to all workers in a cluster from another worker.

node_cluster_broadcast.js

var cluster = require('cluster');
var http = require('http');
var numCPUs = 3;
var workers = [];

if (cluster.isMaster) {
  for (var i = 0; i < numCPUs; i++) {
    workers.push(cluster.fork());
  }

  // rebroadcast a message from a
  // single worker to all other workers
  workers.forEach(function (w, i) {
    w.on('message', function (msg) {
      if ('broadcast' !== msg.type) return;
      workers.forEach(function (w, j) {
        if (i === j) return;
        w.send(msg.body);
      });
    });
  });

  cluster.on('exit', function(worker, code, signal) {
    console.log('worker ' + worker.process.pid + ' died');
  });
} else {

  process.on('message', function (msg) {
    console.log('[%s] %s', process.pid, msg);
  });

  // Workers can share any TCP connection
  // In this case its a HTTP server
  http.createServer(function(req, res) {

    // process.send will not be available
    // if running this worker standalone
    if (process.send) {
      process.send({type: 'broadcast', body: 'hello'});
    }

    res.writeHead(200);
    res.end('ok\n');
  }).listen(8000);
}