System Design 101: Consistent Hashing Explained

Short summary

Consistent hashing solves the redistribution problem in distributed systems by mapping both keys and servers to positions on a hash ring. When a server fails or joins, only the keys between that server and the next server clockwise need remapping—roughly K/N out of K total keys—instead of all keys. This technique is fundamental to building scalable, fault-tolerant systems like Cassandra, DynamoDB, and caching layers.

• •Minimizes key redistribution when cluster size changes (only ~K/N keys remapped vs. all)
• •Maps both keys and servers to a hash ring; queries route to the next server clockwise
• •Essential for building scalable distributed databases and caches (Cassandra, DynamoDB, Redis)

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