1.1.3 • Public • Published


based on Rob's work

A helpful Node module to make it easy to send messages between the master and workers with callbacks.

Events can be emitted by any process and received by any process.


Require the package:

let ClusterMessage = require('cluster_message')
let messages = new ClusterMessage()

Setting up event listeners:

messages.on('multiplication', (data, sendResponse) => {
    sendResponse(data.x * data.y)

Emitting events:

let data = {
    x: Math.round(Math.random()  * 100),
    y: Math.round(Math.random()  * 100)

messages.send('multiplication', data, response => {
    console.log(`${data.x} * ${data.y} = ${response}`)

.send(eventName, data, callback)

  • eventName (string) - the name of the event being emitted
  • data (object) - the object passed to the event listener
  • callback (function) - callback invoked by the event listener, single parameter containing the response
messages.send('print', { name: 'John' }, response => {
    console.log(response) // 'Hi John'

This function will emit an event, the callback is a single parameter that is passed, this means inside the event listener only one parameter can be passed to sendResponse so it needs to be an object containing all the data.

When sent from the master:

  • the event will get sent to all workers
  • each time the worker calls sendResponse (the callback inside the event listener), the callback will be invoked
  • e.g. if there are 3 workers, and all of them call sendResponse, the callback will be invoked 3 times

When sent from the worker:

  • the event is sent to the master only

.on(eventName, callback)

  • eventName (string) - the name of the event to listen for
  • data (object) - single object sent by the event emitter (.send)
  • callback (function) - takes two parameters, data (string) and sendResponse (function). data is the data sent by the event emitter, sendResponse is a function that you invoke and pass the data you want to send back to the callback on the event emitter
messages.on('print', (data, sendResponse) => {
    sendResponse('Hi ' +

This is the event listener, the callback takes two parameters (data and sendResponse). sendResponse only takes one parameter and is sent back to wherever the event originated.

When initiating ClusterMessages you can pass it some options:

let ClusterMessages = require('cluster-messages')

let options = {
  metaKey: '__metadata__',
  callbackTimeout: 1000 * 60 * 10

let messages = new ClusterMessages(options)


Messages are sent around as usual and can be received through cluster.on('message') or process.on('message') as expected, so the module adds a property containing meta data that is passed around with each event. As this meta data property is essentially exposed in every single message event emission within cluster or process, the metaKey option allows you to define the name of the meta data property to ensure it does not conflict with your application.


When a callback is passed to messages.send, it is stored, but in the case that for some reason due to either Node or the OS that the message is dropped when being sent from one process to the other, the callback will never get deleted so the callback is automatically deleted after a set amount of time (default is 10 minutes). This option allows you to specify a timeout in milliseconds. This option is not really necessary at all, but the point of this logic is to prevent memory leaks.

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npm i cluster_communicate

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