Cluster Design & Sharding — Azure DocumentDB

In Azure DocumentDB, a shard key is not required until the database surpasses terabytes. Most scaling decisions are about picking the right M-tier first.

Rules

• cluster-tier-selection — Pick an M-tier (M10–M200+) based on working-set memory, vCPU, and vector-index size.
• cluster-scale-before-shard — Scale vertically first; DocumentDB doesn't require a shard key until TB scale.
• cluster-shard-key-query-aligned — When you do shard at TB scale, pick a high-cardinality, query-aligned, immutable shard key.