Why LLM Inference Needs a New Kind of Router

HTTP routing has been a solved problem for many years. Round-robin, consistent hashing, least-connections. Pick one, put it in front of a pool of identical servers, and the traffic spreads pretty evenly.

To route a request to the pod with the best cached prefix, you need to know which blocks are cached on which pod. That sounds simple until you look at the numbers. You may have hundreds of pods, each with thousands of cached blocks. State can change hundreds of times per second. Across this complexity, queries need to return in microseconds because they sit on the critical path of every inference request.