Load Balancers are some of the most expensive bits of equipment small to medium size sites are likely to buy, even more expensive than database servers.
Since I help a number of smaller and young startups a good Open Source load balancer is essential, I use HAProxy for this purpose.
HAProxy is a high performance non threaded load balancer, it supports a lot of really excellent features like regular expression based logic to route certain types of requests to different backend servers, session tracking using cookies or URL parts and has extensive documentation.
Getting a full redundant set of load balancers going with it requires the help of something like Linux-HA which I use extensively for this purpose, the combination of HAProxy and Linux-HA gives you a full active-passive cluster with failover capabilities that really does work a charm.
I recently had to reload a HAProxy instance after about a 100 day uptime, its performance stats were 1.8 billion requests, 15TB out and just short of 2TB in
Worth checking out HAProxy before shelling out GBP15 000 for 2 x hardware load balancers.
