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