Load Balancing in Amazon EC2?

Question

We've been fighting with HAProxy for a few days now in Amazon EC2; the experience has so far been great, but we're stuck on squeezing more performance out of the software load balancer. We're not exactly Linux networking whizzes (we're a .NET shop, normally), but we've so far held our own, attempting to set proper ulimits, inspecting kernel messages and tcpdumps for any irregularities. So far though, we've reached a plateau of about 1,700 requests/sec, at which point client timeouts abound (we've been using and tweaking httperf for this purpose). A coworker and I were listening to the most recent Stack Overflow podcast, in which the Reddit founders note that their entire site runs off one HAProxy node, and that it so far hasn't become a bottleneck. Ack! Either there's somehow not seeing that many concurrent requests, we're doing something horribly wrong, or the shared nature of EC2 is limiting the network stack of the Ec2 instance (we're using a large instance type). Considering the fact that both Joel and the Reddit founders agree that network will likely be the limiting factor, is it possible that's the limitation we're seeing?

Any thoughts are greatly appreciated!

Answer 1

In case you aren't seeing a 100% CPU usage, then you are probably network bound. Amazon EC2 uses gigabit network internally so you could try an XL instance and you will have the underlying hardware to yourself. With the underlying hardware all to yourself, you won't have to share that gigabit network port anymore. If the shared network stack is, in fact, the limitation you are facing then this should help.