Consistent Hashing

maang.io System Design Series

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Consistent hashing maps both keys and nodes onto the same circular hash space, so each key is owned by the next node clockwise. Its superpower: when a node joins or leaves, only the keys in its immediate arc move — roughly 1/N of the data — instead of the near-total reshuffle that plain hash % N inflicts. It's the distribution engine inside Cassandra, DynamoDB, memcached clients, and CDNs.

This deep dive comes in three parts:

• Foundations & Core Concepts — the ring, clockwise ownership, and why hash % N falls apart.
• Internals — virtual nodes for balance, remapping math, and bounded-load variants, with worked numbers.
• Interview — Staff/Principal Q&A: rebalancing, hot spots, and where it shows up in real designs.