ps: I wonder if it's related, maybe cloudflare uses netbsd and pushed for kernel embedding, or they just benefited from netbsd lua love.
We use Lua for the WAF (as Mike says), but also for all request processing. This is in part because we use Nginx and in part because employ agentzh (http://agentzh.org/) and he works on OpenResty. Fairly recently we moved all processing of requests through CloudFlare to a Lua-based system inside Nginx.
That's >5B pages views per 24 hours going through LuaJIT-ed code.
I'll add a more serious question. This is a nice optimization, but wouldn't clever attackers respond in turn by eventually throwing highly varied traffic patterns to fluster the JIT?
If that were to happen (and I think it's a big "if" because of the complexity of predicting what will throw it off given that the attacker doesn't know the code we are running) then we'd see the WAF latency increase and alarms would be generated immediately. That, in turn, would cause a bunch of other mechanisms to come into play.
Thanks for your answer. Its a very neat setup. (My intuition is that its not a case of if but when, but you've probably won yourself quite a bit of time until that happens)
The honest truth is that I actually don't know how many servers we have because it's not a number that I have to worry about.
I do know that floor(log_10(#servers)) = 2.