I thought I'd share some information on one of the technologies we use for our larger sites HAProxy.

I know many agencies naturally try and avoid getting involved in Infrastructure but I'm a believer in understanding all elements of the stack that you build your applications on, the i'll just shove it in the cloud works in theory only.

So when we needed a solution to do load balancing recently rather than go and buy the latest piece of Cisco kit or use our standard KEEPALIVED setup I hunted around.

The interesting challenge was that we wanted to do more than simple IP based load balancing, we needed something which was essentially application aware. Having looked at Zeus which we used back in 2006 for a large University client and discounted it I looked at HAPROXY.

HaProxy is essentially a reverse proxy than can do either TCP or HTTP based load balancing, its super fast and very elegant. We run it up on Centos on some moderate VMs and it hums away using next to no resources.

You can learn more about it here http://haproxy.1wt.eu/

There is a useful monitoring tool here http://feurix.org/projects/hatop/

Needless to say we have it in production for a few clients including a new Social networking startup.

My particular favourite feature is the ability to do rule based sticky sessions which for example only take affect after a user has done a post or based on the existance of certain cookies.

HAProxy plays very nicely with VarnishCache and Ngnix which I'll blog about another time.