Production Cluster ArchitectureΒΆ

In a production cluster, you must ensure that data is redundant and that your systems are highly available. To that end, a production cluster must have the following components:

  • Config Servers

    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.

    A single sharded cluster must have exclusive use of its config servers. If you have multiple sharded clusters, each cluster must have its own replica set config servers.

  • Two or More Replica Sets As Shards

    These replica sets are the shards. For information on replica sets, see Replication.

  • One or More Query Routers (mongos)

    The mongos instances are the routers for the cluster. Typically, deployments have one mongos instance on each application server.

    You may also deploy a group of mongos instances and use a proxy/load balancer between the application and the mongos. In these deployments, you must configure the load balancer for client affinity so that every connection from a single client reaches the same mongos.

    Because cursors and other resources are specific to an single mongos instance, each client must interact with only one mongos instance.

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.

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