Sharded Cluster Components

Sharded clusters implement sharding. A sharded cluster consists of the following components:

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

Config servers hold metadata about the sharded cluster. The metadata maps chunks to shards.

Changed in version 3.2: Starting in MongoDB 3.2, config servers for sharded clusters can be deployed as a replica set. The replica set config servers must run the WiredTiger storage engine. MongoDB 3.2 deprecates the use of three mirrored mongod instances for config servers.

For more information, see Config Servers.

mongos Instances
mongos instances route 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.

Further Reading

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.

To deploy a sharded cluster, see Deploy a Sharded Cluster.

←   Sharding Concepts Shards  →

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