Something that isn't quite clicking for me from this article, and my other knowledge of cloudflare... So you have Nd DNS IPs, Nc Cache IPs, Np Proxy Ips and so

Something that isn't quite clicking for me from this article, and my other knowledge of cloudflare... So you have Nd DNS IPs, Nc Cache IPs, Np Proxy Ips and so on, plus some failovers. It seems to me you can only have Sum(Nsubscript) + M servers in any given pop. Which is all good, but I presume that the load on proxy and cache servers would be such that you'd need quite a few instances of each. Further, given the nature of cloudflare's services, it would seem that some CDNed sites would be heavier than others. So how do you assign various sites to IPs? Is this via some dynamic DNS magic? Is there a lot of communication between proxy and cache instances at each pop (DHT or similar?). Basically, what I'm saying is, using BGP to do most of the load balancing is awesome, but it seems there has to be more to it than that, otherwise you'd experience a lot of flapping between servers handling heavy sites. That or I'm missing something, but what?