Node.js on multi-core machines

Question

Node.js looks interesting, BUT I must miss something - isn't Node.js tuned only to run on a single process and thread?

Then how does it scale for multi-core CPUs and multi-CPU servers? After all, it is all great to make fast as possible single-thread server, but for high loads I would want to use several CPUs. And the same goes for making applications faster - seems today the way is use multiple CPUs and parallelize the tasks.

How does Node.js fit into this picture? Is its idea to somehow distribute multiple instances or what?

Answer 1

As mentioned above, Cluster will scale and load-balance your app across all cores.

adding something like

cluster.on('exit', function () {
  cluster.fork();
});

Will restart any failing workers.

These days, a lot of people also prefer PM2, which handles the clustering for you and also provides some cool monitoring features.

Then, add Nginx or HAProxy in front of several machines running with clustering and you have multiple levels of failover and a much higher load capacity.

Answer 2

Future version of node will allow you to fork a process and pass messages to it and Ryan has stated he wants to find some way to also share file handlers, so it won't be a straight forward Web Worker implementation.

At this time there is not an easy solution for this but it's still very early and node is one of the fastest moving open source projects I've ever seen so expect something awesome in the near future.

Answer 3

It's possible to scale NodeJS out to multiple boxes using a pure TCP load balancer (HAProxy) in front of multiple boxes running one NodeJS process each.

If you then have some common knowledge to share between all instances you could use a central Redis store or similar which can then be accessed from all process instances (e.g. from all boxes)

Answer 4

Node Js is supporting clustering to take full advantages of your cpu. If you are not not running it with cluster, then probably you are wasting your hardware capabilities.

Clustering in Node.js allows you to create separate processes which can share same server port. For example, if we run one HTTP server on Port 3000, it is one Server running on Single thread on single core of processor.

Code shown below allow you to cluster your application. This code is official code represented by Node.js.

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

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

    Object.keys(cluster.workers).forEach(function(id) {
        console.log("I am running with ID : " + cluster.workers[id].process.pid);
    });

    cluster.on('exit', function(worker, code, signal) {
        console.log('worker ' + worker.process.pid + ' died');
    });
} else {

    //Do further processing.
}

check this article for the full tutorial

Answer 5

You may run your node.js application on multiple cores by using the cluster module on combination with os module which may be used to detect how many CPUs you have.

For example let's imagine that you have a server module that runs simple http server on the backend and you want to run it for several CPUs:

// Dependencies.
const server = require('./lib/server'); // This is our custom server module.
const cluster = require('cluster');
const os = require('os');

 // If we're on the master thread start the forks.
if (cluster.isMaster) {
  // Fork the process.
  for (let i = 0; i < os.cpus().length; i++) {
    cluster.fork();
  }
} else {
  // If we're not on the master thread start the server.
  server.init();
}

Answer 6

The new kid on the block here is LearnBoost's "Up".

It provides "Zero-downtime reloads" and additionally creates multiple workers (by default the number of CPUs, but it is configurable) to provide the best of all Worlds.

It is new, but seems to be pretty stable, and I'm using it happily in one of my current projects.