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. For more information see Shards.
Config Servers: Each config server is a mongod instance that holds metadata about the cluster. The metadata maps chunks to shards. For more information, see Config Servers.
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. For more information see Sharded Cluster Query Routing.

Enable sharding in MongoDB on a per-collection basis. For each collection you shard, you will specify a shard key for that collection.

Further Reading¶