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Add Shards to a Cluster

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  • Considerations
  • Add a Shard to a Cluster

You add shards to a sharded cluster after you create the cluster or any time that you need to add capacity to the cluster. If you have not created a sharded cluster, see Deploy a Sharded Cluster.

In production environments, all shards should be replica sets.

When you add a shard to a sharded cluster, you affect the balance of chunks among the shards of a cluster for all existing sharded collections. The balancer will begin migrating chunks so that the cluster will achieve balance. See Balancer Internals for more information.

When adding a shard to a cluster, always ensure that the cluster has enough capacity to support the migration required for balancing the cluster without affecting legitimate production traffic.

You interact with a sharded cluster by connecting to a mongos instance.

  1. In mongosh, connect to the mongos instance. For example, if a mongos is accessible at on port 27017, issue the following command:

    mongosh --host --port 27017
  2. Add a shard to the cluster using the sh.addShard() method, as shown in the examples below. Issue sh.addShard() separately for each shard. If the shard is a replica set, specify the name of the replica set and specify a member of the set. In production deployments, all shards should be replica sets.



    You can instead use the addShard database command, which lets you specify a name and maximum size for the shard. If you do not specify these, MongoDB automatically assigns a name and maximum size. To use the database command, see addShard.

    The following are examples of adding a shard with sh.addShard():

    • To add a replica set shard named rs1 with a member running on port 27018 on, issue the following command:

      sh.addShard( "rs1/" )
    • To add a standalone mongod shard running on port 27018 of, issue the following command:

      sh.addShard( "" )


    It might take some time for chunks to migrate to the new shard.


Migrate a Sharded Cluster to Different Hardware


Add a Member to a Shard