clusterhub/README.md

Easily and efficiently sync data in your cluster applications.

# clusterhub

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

[![Build Status](https://secure.travis-ci.org/fent/clusterhub.svg)](http://travis-ci.org/fent/clusterhub)
[![Dependency Status](https://david-dm.org/fent/clusterhub.svg)](https://david-dm.org/fent/clusterhub)
[![codecov](https://codecov.io/gh/fent/clusterhub/branch/master/graph/badge.svg)](https://codecov.io/gh/fent/clusterhub)


# Usage

```js
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][eventvat].

# Motive

Node.js is a perfect candidate to developing [Date Intensive Real-time Applications](http://video.nextconf.eu/video/1914374/nodejs-digs-dirt-about). 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](https://github.com/fent/socket.io-clusterhub) - Sync data between multi-process socket.io applications.
* [clusterchat](https://github.com/fent/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](http://nodejs.org/docs/latest/api/events.html#events.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.

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

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

All functions from [EventVat][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.

[eventvat]: https://github.com/hij1nx/EventVat

#### worker process

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

#### master process
```js
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](https://mochajs.org)

```bash
npm test
```