Sharded Cluster Components
Sharded clusters implement sharding. A sharded cluster consists of the following components:
- Shards – A shard is a MongoDB instance that holds a subset of a collection’s data. Each shard is either a single mongod instance or a replica set. In production, all shards are replica sets.
- Config Servers – Each config server is a mongod instance that holds metadata about the cluster. The metadata maps chunks to shards.
- Routing Instances – Each router is a mongos instance that routes the reads and writes from applications to the shards. Applications do not access the shards directly.
Diagram of a sharded cluster.
Enable sharding in MongoDB on a per-collection basis. For each collection you shard, you will specify a shard key for that collection.
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