How do I use Node.js clusters with my simple Express app?

javascript node.js redis express cluster-computing

11,412

Actually, your workload is not really I/O bound: it is CPU bound due to the cost of jade-based dynamic page generation. I cannot guess the complexity of your jade template, but even with simple templates, generating HTML pages is expensive.

For my tests I used this template:

html(lang="en")
  head
    title Example
  body
    h1 Jade - node template engine
    #container
      ul#users
        each user in items
          li User:#{user}

I added 100 dummy strings to the items key in Redis.

On my box, I get 475 req/s with node.js CPU at 100% (which means 50% CPU consumption on this dual core box). Let's replace:

res.render( 'index', { items: items } );

by:

res.send( '<html lang="en"><head><title>Example</title></head><body><h1>Jade - node template engine</h1><div id="container"><ul id="users"><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li><li>User:NOTHING</li></ul></div></body></html>' );

Now, the result of the benchmark is close to 2700 req/s. So the bottleneck is clearly due to the formatting of the HTML page.

Using the cluster package in this situation is a good idea, and it is straightforward. The code can be modified as follows:

var cluster = require('cluster')

if ( cluster.isMaster ) {
  for ( var i=0; i<2; ++i )
    cluster.fork();
} else {
  var
      express = require( 'express' ),
      app     = express.createServer(),
      redis   = require( 'redis' ).createClient();

  app.configure( function() {
      app.set( 'view options', { layout: false } );
      app.set( 'view engine', 'jade' );
      app.set( 'views', __dirname + '/views' );
      app.use( express.bodyParser() );
  });

  function log( what ) { console.log( what ); }

  app.get( '/', function( req, res ) {
      redis.lrange( 'items', 0, 50, function( err, items ) {
            if( err ) { log( err ); } else {
              res.render( 'index', { items: items } );
            }
      });
  });

  app.listen( 8080 );
}

Now the result of the benchmark is close to 750 req/s with 100 % CPU consumption (to be compared with the initial 475 req/s).

11,412

vjk2005

I design and develop web apps and Chrome extensions. Tools of choice are Node.js + MongoDB for the server-side and standard JS/Jquery for the client-side.

Updated on June 14, 2022

Comments

vjk2005 almost 2 years
— I built a simple app that pulls in data (50 items) from a Redis DB and throws it up at localhost. I did an ApacheBench (c = 100, n = 50000) and I'm getting a semi-decent 150 requests/sec on a dual-core T2080 @ 1.73GHz (my 6 y.o laptop), but the proc usage is very disappointing as shown:

Only one core is used, which is as per design in Node, but I think I can nearly double my requests/sec to ~300, maybe even more, if I can use Node.js clusters. I fiddled around quite a bit but I haven't been able to figure out how to put the code given here for use with my app which is listed below:
```
var 
    express = require( 'express' ),
    app     = express.createServer(),
    redis   = require( 'redis' ).createClient();

app.configure( function() {
    app.set( 'view options', { layout: false } );
    app.set( 'view engine', 'jade' );
    app.set( 'views', __dirname + '/views' );
    app.use( express.bodyParser() );
} );

function log( what ) { console.log( what ); }

app.get( '/', function( req, res ) {
    redis.lrange( 'items', 0, 50, function( err, items ) {
            if( err ) { log( err ); } else {
                res.render( 'index', { items: items } );
            }
    });
});

app.listen( 8080 );
```
I also want to emphasize that the app is I/O intensive (not CPU-intensive, which would've made something like threads-a-gogo a better choice than clusters).

Would love some help in figuring this out.
vjk2005 almost 12 years

wow, thanks!, that worked really well — imgur.com/Cpqy6 — I spent most of yesterday pushing it from 80 to 150 and now a simple if block is making all that work look like peanuts. The note about templates was very educational; I knew there would be some cost but didn't think it'd be "475 to 2700" big. Can I optimize Express? Btw, I also wanted to share the CPU stats — imgur.com/n7WPv — I went as high as 15 workers but both cores never went to 100%. I haven't enabled Redis persistence so it shouldn't touch the disk, but around the 30K-request mark my disk spins crazy. Am I overlooking something?
Didier Spezia almost 12 years

With a dual core box, the optimal number of worker processes is 2. I don't know how much memory you have, but if you start too many workers, you may trigger swapping. On my box, one node process takes around 50 MB in memory.
Didier Spezia almost 12 years

The performance bottleneck is not express but jade. You could try another templating engine (still working with express). Here is a list: github.com/joyent/node/wiki/modules#wiki-templating
vjk2005 almost 12 years

oh no, by "I went as high as 15 workers" — I meant I started at 2, as listed in your answer, & worked my way up through 3, 4, 5 and gave up at 15; none of those configs saw both the cores reach 100% simultaneously, which got me wondering if I was doing something wrong.
vjk2005 almost 12 years

"The performance bottleneck is not express but jade." — whoops, I meant "jade" but said "express". What according to you is faster than Jade?
vjk2005 almost 12 years

" I don't know how much memory you have, but if you start too many workers, you may trigger swapping." — I have 1.5 GB out of which it used up 500 MB with swap around 260 MB out of 3.5 GB. Puzzler.
vjk2005 almost 12 years

Just to close out the discussion on templates, I found this benchmark of different template engines — paularmstrong.github.com/node-templates/benchmarks.html, handy for those hitting this question who wish to improve their template performance as well.
Didier Spezia almost 12 years

According to my own benchmark, the fastest ones are Swig, nTenjin, thunder and doT in that order.
vjk2005 almost 12 years

Alrighty, I'll check out Swig and will update here if the I get significant improvements over Jade. Thanks again, Didier.
Aleksei Zabrodskii over 11 years

You should try NODE_ENV=production node app.js instead of node app.js .