Consistent hashing (or more generally weighted rendezvous hashing) provides pseudorandom allocations with minimal reallocations when parameters change. This is

Consistent hashing (or more generally weighted rendezvous hashing) provides pseudorandom allocations with minimal reallocations when parameters change. This is exactly the properties desired for rolling out feature flags gradually over an input space like user IDs. It is a special case of a consistent hash function, where the possible assignments are just two (weighted) buckets, corresponding to the feature flag's value of true/false.