clusterhub

clusterhub

An attempt at giving multi process node programs a simple and efficient way to share data.

Usage

const cluster = require('cluster');
const numCPUs = require('os').cpus().length;
const hub = require('clusterhub');

if (cluster.isMaster) {
  // Fork workers.
  for (let i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

} else {
  hub.on('event', (data) => {
    // do something with `data`
  });

  // emit event to all workers
  hub.emit('event', { foo: 'bar' });
}

Features

• Efficient event emitter system. Clusterhub will not send an event to a process that isn't listening for it. Events from the same process of a listener will be emitted synchronously.
• In process database. Each hub has its own instance of a redis-like database powered by EventVat.

Motive

Node.js is a perfect candidate to developing Date Intensive Real-time Applications. Load balancing in these applications can become complicated when having to share data between processes.

A remote database can be an easy solution for this, but it's not the most optimal. Communicating with a local process is several times faster than opening remote requests from a database. And even if the database is hosted locally, the overhead of communicating with yet another program is lessened.

Note that this module is experimental. It currently works by using a process's internal messaging system.

Made with Clusterhub

• socket.io-clusterhub - Sync data between multi-process socket.io applications.
• clusterchat - A multi-process chat that shows off socket.io-clusterhub.

API

hub.createHub(id)

Clusterhub already comes with a default global hub. But you can use this if you want to create more.

Hub#destroy()

Call to disable hub from emitting and receiving remote messages/commands.

Additionally, all functions from the regular EventEmitter are included. Plus a couple of extras.

Hub#emitLocal(event, ...args)

Emit an event only to the current process.

Hub#emitRemote(event, ...args)

Emit an event only to other worker processes and master. Or only to workers if the current process is the master.

hub.on('remotehello', () => {
  // Hello from another process.
});

hub.emitRemote('remotehello', { hello: 'there' });

All functions from EventVat are included as well. Their returned value can be accessed by providing a callback as the last argument. Or optionally by its returned value if called by the master.

worker process

hub.set('foo', 'bar', () => {
  hub.get('foo', (val) => {
    console.log(val === 'bar'); // true
  });
});

master process

let returnedVal = hub.incr('foo', (val) => {
  // Can be given a callback for consistency.
  console.log(val === 1); // true
});

// But since it's the master process it has direct access to the database.
console.log(returnedVal === 1); // true

Install

npm install clusterhub

Tests

Tests are written with mocha

npm test