Sharded Cluster Components

A MongoDB sharded cluster consists of the following components:

  • shard: Each shard contains a subset of the sharded data. Each shard can be deployed as a replica set.
  • mongos: The mongos acts as a query router, providing an interface between client applications and the sharded cluster.
  • config servers: Config servers store metadata and configuration settings for the cluster. As of MongoDB 3.4, config servers must be deployed as a replica set (CSRS).

Production Configuration

In a production cluster, ensure that data is redundant and that your systems are highly available. Consider the following for a production sharded cluster deployment:

Where possible, consider deploying one member of each replica set in a site suitable for being a disaster recovery location.

Sharding requires at least two shards to distribute sharded data. Single shard sharded clusters may be useful if you plan on enabling sharding in the near future, but do not need to at the time of deployment.

You can deploy a mongos router on each application server to ensure each server has consistent access to the sharded cluster. Alternatively, deploy a group of mongos routers and use a proxy or load balancer between the application and the mongos group. In these deployments, you must configure the load balancer for client affinity such that every connection from a single client reaches the same mongos.

Diagram of a sample sharded cluster for production purposes.  Contains exactly 3 config servers, 2 or more ``mongos`` query routers, and at least 2 shards. The shards are replica sets.

Development Configuration

For testing and development, you can deploy a sharded cluster with a minimum number of components. These non-production clusters have the following components:

Diagram of a sample sharded cluster for testing/development purposes only.  Contains only 1 config server, 1 ``mongos`` router, and at least 1 shard. The shard can be either a replica set or a standalone ``mongod`` instance.

Warning

Use the test cluster architecture for testing and development only.

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