Consistent hashing is a bit cleaner way to do it, but pretty much the same result as modulo-ing the user id against number of servers. At least as I understand it, you consistently hash something (a user id, a request URL, etc) into N buckets, where N is the number of servers, so changing N re-shuffles all of the buckets anyway.
Short of something like cassandra's ring topology, how would you use consistent hashing add new servers and assign them requests?
