What's the most efficient node.js inter-process communication library/method?

We have few node.js processes that should be able to pass messages, What's the most efficient way doing that? How about using node_redis pub/sub

EDIT: the processes might run on different machines

If you want to send messages from one machine to another and do not care about callbacks then Redis pub/sub is the best solution. It's really easy to implement and Redis is really fast.

First you have to install Redis on one of your machines.

Its really easy to connect to Redis:

var client = require('redis').createClient(redis_port, redis_host);

But do not forget about opening Redis port in your firewall!

Then you have to subscribe each machine to some channel:

client.on('ready', function() {
  return client.subscribe('your_namespace:machine_name');
});

client.on('message', function(channel, json_message) {
  var message;
  message = JSON.parse(message);
  // do whatever you vant with the message
});

You may skip your_namespace and use global namespace, but you will regret it sooner or later.

It's really easy to send messages, too:

var send_message = function(machine_name, message) {
  return client.publish("your_namespace:" + machine_name, JSON.stringify(message));
};

If you want to send different kinds of messages, you can use pmessages instead of messages:

client.on('ready', function() {
  return client.psubscribe('your_namespace:machine_name:*');
});

client.on('pmessage', function(pattern, channel, json_message) {
  // pattern === 'your_namespace:machine_name:*'
  // channel === 'your_namespace:machine_name:'+message_type
  var message = JSON.parse(message);
  var message_type = channel.split(':')[2];
  // do whatever you want with the message and message_type
});

send_message = function(machine_name, message_type, message) {
  return client.publish([
    'your_namespace',
    machine_name,
    message_type
  ].join(':'), JSON.stringify(message));
};

The best practice is to name your processes (or machines) by their functionality (e.g. 'send_email'). In that case process (or machine) may be subscribed to more than one channel if it implements more than one functionality.

Actually, it's possible to build a bi-directional communication using redis. But it's more tricky since it would require to add unique callback channel name to each message in order to receive callback without losing context.

So, my conclusion is this: Use Redis if you need "send and forget" communication, investigate another solutions if you need full-fledged bi-directional communication.

Why not use ZeroMQ/0mq for IPC? Redis (a database) is over-kill for doing something as simple as IPC.

Quoting the guide:

> ØMQ (ZeroMQ, 0MQ, zmq) looks like an embeddable networking library > but acts like a concurrency framework. It gives you sockets that carry > atomic messages across various transports like in-process, > inter-process, TCP, and multicast. You can connect sockets N-to-N with > patterns like fanout, pub-sub, task distribution, and request-reply. > It's fast enough to be the fabric for clustered products. Its > asynchronous I/O model gives you scalable multicore applications, > built as asynchronous message-processing tasks.

The advantage of using 0MQ (or even vanilla sockets via net library in Node core, minus all the features provided by a 0MQ socket) is that there is no master process. Its broker-less setup is best fit for the scenario you describe. If you are just pushing out messages to various nodes from one central process you can use PUB/SUB socket in 0mq (also supports IP multicast via PGM/EPGM). Apart from that, 0mq also provides for various different socket types (PUSH/PULL/XREP/XREQ/ROUTER/DEALER) with which you can create custom devices.

Start with this excellent guide: http://zguide.zeromq.org/page:all

For 0MQ 2.x:

http://github.com/JustinTulloss/zeromq.node

For 0MQ 3.x (A fork of the above module. This supports PUBLISHER side filtering for PUBSUB):

http://github.com/shripadk/zeromq.node

More than 4 years after the question being ask there is an interprocess communication module called node-ipc. It supports unix/windows sockets for communication on the same machine as well as TCP, TLS and UDP, claiming that at least sockets, TCP and UDP are stable.

Here is a small example taken from the documentation from the github repository:

Server for Unix Sockets, Windows Sockets & TCP Sockets

var ipc=require('node-ipc');

ipc.config.id   = 'world';
ipc.config.retry= 1500;

ipc.serve(
    function(){
        ipc.server.on(
            'message',
            function(data,socket){
                ipc.log('got a message : '.debug, data);
                ipc.server.emit(
                    socket,
                    'message',
                    data+' world!'
                );
            }
        );
    }
);

ipc.server.start();

Client for Unix Sockets & TCP Sockets

var ipc=require('node-ipc');

ipc.config.id   = 'hello';
ipc.config.retry= 1500;

ipc.connectTo(
    'world',
    function(){
        ipc.of.world.on(
            'connect',
            function(){
                ipc.log('## connected to world ##'.rainbow, ipc.config.delay);
                ipc.of.world.emit(
                    'message',
                    'hello'
                )
            }
        );
        ipc.of.world.on(
            'disconnect',
            function(){
                ipc.log('disconnected from world'.notice);
            }
        );
        ipc.of.world.on(
            'message',
            function(data){
                ipc.log('got a message from world : '.debug, data);
            }
        );
    }
);

Im currently evaluating this module for a replacement local ipc (but could be remote ipc in the future) as a replacement for an old solution via stdin/stdout. Maybe I will expand my answer when I'm done to give some more information how and how good this module works.

i would start with the built in functionality that node provide.
you can use process signalling like:

process.on('SIGINT', function () {
  console.log('Got SIGINT.  Press Control-D to exit.');
});

this signalling

> Emitted when the processes receives a signal. See sigaction(2) for a > list of standard POSIX signal names such as SIGINT, SIGUSR1, etc.

Once you know about process you can spwn a child-process and hook it up to the message event to retrive and send messages. When using child_process.fork() you can write to the child using child.send(message, [sendHandle]) and messages are received by a 'message' event on the child.

Also - you can use cluster. The cluster module allows you to easily create a network of processes that all share server ports.

var cluster = require('cluster');
var http = require('http');
var numCPUs = require('os').cpus().length;

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

  cluster.on('exit', function(worker, code, signal) {
    console.log('worker ' + worker.process.pid + ' died');
  });
} else {
  // Workers can share any TCP connection
  // In this case its a HTTP server
  http.createServer(function(req, res) {
    res.writeHead(200);
    res.end("hello world\n");
  }).listen(8000);
}

For 3rd party services you can check: hook.io, signals and bean.

take a look at node-messenger

https://github.com/weixiyen/messenger.js

will fit most needs easily (pub/sub ... fire and forget .. send/request) with automatic maintained connectionpool

we are working on multi-process node app, which is required to handle large number of real-time cross-process message.

We tried redis-pub-sub first, which failed to meet the requirements.

Then tried tcp socket, which was better, but still not the best.

So we switched to UDP datagram, that is much faster.

Here is the code repo, just a few of lines of code. https://github.com/SGF-Games/node-udpcomm