Hundreds of servers in 23 locations worldwide, each server running multiple instances of Nginx: http://blog.cloudflare.com/a-tour-inside-cloudflares-latest-... The key fact is that this type of scale is possible with Nginx + Lua + hundreds (not thousands) of servers.

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.