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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.
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.

Further Reading

Shards
A shard is a single server or replica set that holds a part of the sharded collection.
Config Servers
Config servers hold the metadata about the cluster, such as the shard location of the data.

Deploy a sharded cluster, see Deploy a Sharded Cluster.

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