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Simple message passing between cluster master and workers in Node.js
var cluster = require('cluster');
if (cluster.isWorker) {
console.log('Worker ' + + ' has started.');
// Send message to master process.
process.send({msgFromWorker: 'This is from worker ' + + '.'})
// Receive messages from the master process.
process.on('message', function(msg) {
console.log('Worker ' + + ' received message from master.', msg);
if (cluster.isMaster) {
console.log('Master ' + + ' has started.');
// Fork workers.
for (var i = 0; i < 2; i++) {
var worker = cluster.fork();
// Receive messages from this worker and handle them in the master process.
worker.on('message', function(msg) {
console.log('Master ' + + ' received message from worker ' + + '.', msg);
// Send a message from the master process to the worker.
worker.send({msgFromMaster: 'This is from master ' + + ' to worker ' + + '.'});
// Be notified when worker processes die.
cluster.on('death', function(worker) {
console.log('Worker ' + + ' died.');

thanks! great ref.

jnovack commented Aug 7, 2013

This won't work. var inside for?

worker will hold the last worker forked, not each one (specially inside the event callback).

dazld commented Feb 5, 2014

should work fine, as the variable is only being used inside that particular block. if it was leaking outside the block, then yes, it would be a problem (and should be in a closure, or have some kind of binding). nice example, thanks!

ynkm169 commented Aug 25, 2014

how do u pass message between workers.....pass message to master makes master a bottleneck..............

Good example.
Need to replace for on newer Node versions.
Same for

chbdetta commented Aug 2, 2015

Great example. Thanks a lot!

danieldram commented Jun 10, 2016

can use os.cpus().length to get number of running workers if you do not know the exact number as indicated in the for loop.
(Be sure to var os = require('os') when using)

saeidalidadi commented Feb 6, 2017

I have a Map() object which I use to store on fly values for my app so how I can share this object between all workers ?
I am using .set() and .get() methods of this object also.

Rob-- commented Jun 4, 2017

I've created a module to make communicating between the master and worker easier:

vikene commented Jun 8, 2017

Great! thanks 👍

Why would workers need to communicate between other workers? Shouldn't the database be the single point of truth that each worker gets any persisted data from?

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