[jiggawatts]

Locality and latency.

Network hops are not free! Those milliseconds are an eternity compared to local function calls.

The optimal architecture is something like what Service Fabric or Orleans can do with their distributed dictionary types: reads are generally in-process and take only nanoseconds (but writes require a synchronous replica copy to a remote host.)

Obviously this requires load balancers to steer traffic consistently, but that’s a common feature… outside of the public clouds where they forgot latency exists.