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

Question

— 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

Answer 1

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( '
Jade - node template engine
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
User:NOTHING
' );

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).