Multi-Region LLM Serving: The Cache Locality Problem Nobody Warns You About
When you run a stateless HTTP API across multiple regions, the routing problem is essentially solved. Put a global load balancer in front, distribute requests by geography, and the worst thing that happens is a slightly stale cache entry. Any replica can serve any request with identical results.
LLM inference breaks every one of these assumptions. The moment you add prompt caching — which you will, because the cost difference between a cache hit and a cache miss is roughly 10x — your service becomes stateful in ways that most infrastructure teams don't anticipate until they're staring at degraded latency numbers in their second region.
