"Load Balancing in the Cloud" whitepaper by Rightscale

Rightscale recently published a whitepaper titled "Load Balancing in the Cloud: Tools, Tips and Techniques" (you can get it from here, however registration is required). I found out about it from this post on the Rightscale blog which is a good introduction to the paper. Here are some things I found interesting in the paper:

• they tested HAProxy, Zeus Technologies Load Balancer, aiCache's Web Accelerator and Amazon's Elastic Load Balancer (ELB), all deployed in Amazon EC2
• the connection rate (requests/second) was the metric under test, because it turns out it's usually the limiting factor when deploying a LB in the cloud
• it was nice to see HAProxy as pretty much the accepted software-based Open Source solution for load balancing in the cloud (the other LBs tested are not free/open source)
• the load testing methodology was very sound, and it's worth studying; Brian Adler, the author of the whitepaper, clearly knows what he's doing, and he made sure he eliminated potential bottlenecks along the paths from load-generating clients to the Web servers behind the LB
• ab and httperf were used to generate load
• all the non-ELB solutions resulted in 5,000 requests/sec on average (Zeus was slightly better than HAProxy, 6.5K vs. 5.2K req/sec)
• ELB was shown to be practically 'infinitely' scalable (for some value of infinity); however, the elasticity of ELB is gradual, so if you experience a sudden traffic spike, ELB might catch up too slowly for your needs
• for slow and steady traffic increase though ELB seems to be ideal
• it turns out that 100,000 packets/second total throughput (inbound + outbound) is a hard limit in EC2 and it is due to virtualization
• so...if your Web traffic exceeds this limit, you need to deploy multiple load balancers (or use ELB of course); when I was at OpenX, we did just that by deploying multiple HAProxy instances and using DNS round-robin to load balance traffic across our load balancers

Overall, if you're interested in deploying high traffic Web sites in the cloud, I think it's worth your time to register and read the whitepaper.