The Problem
Simple modulo hashing breaks whenever the node count changes. Nearly every key moves, which is disastrous for caches and sharded stores.
The Ring
Consistent hashing places both keys and nodes on a circular ring. A key belongs to the first node clockwise from its hash position.
Why It Helps
When you add or remove a node, only the keys in that node’s segment move. That is a much smaller blast radius than modulo hashing.
Virtual Nodes
Virtual nodes improve balance and reduce hot spots by giving each physical machine multiple positions on the ring.
Where It Appears
You see consistent hashing in caches, distributed databases, message brokers, and CDNs.
Final Shape
The clean interview answer is: use a ring, walk clockwise for ownership, and add vnodes so load spreads more evenly across the cluster.