Shared Nothing

Signals come from the outside world. Send 'em to a whole bunch of machines that share no disk, memory, cpu, nothing. Serve your responses without resource contention between machines with the possible exception of MemCached style caching.

If you need to combine some of those signals together to generate a SourceOfTruth, replicate 'em in your switches and send 'em to a machine that does that. When you need to, stage round-robin downloading new back ends to your server farm.

Scale to global size like Google.