Systems Lab
A provisioning service assigns each host to one of a handful of shards. Add or remove a shard and watch how many hosts get reassigned. The difference between consistent hashing and naive modulo hashing is the whole reason large fleets can scale without a full reshuffle every time.
Consistent hashing: shards and hosts sit on the same ring. Each host belongs to the next shard clockwise, so adding or removing a shard only reassigns the hosts between it and its neighbour.