Add Shards 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.

Considerations¶

Balancing¶

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 Sharded Collection Balancing for more information.

Capacity Planning¶

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.

Add a Shard to a Cluster¶

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

From a mongo shell, connect to the mongos instance. For example, if a mongos is accessible at mongos0.example.net on port 27017, issue the following command:
```
mongo --host mongos0.example.net --port 27017
```
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.

Optional

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 shard for a replica set named rs1 with a member running on port 27017 on mongodb0.example.net, issue the following command:
```
sh.addShard( "rs1/mongodb0.example.net:27017" )
```
  Changed in version 2.0.3.
  
  For MongoDB versions prior to 2.0.3, you must specify all members of the replica set. For example:
```
sh.addShard( "rs1/mongodb0.example.net:27017,mongodb1.example.net:27017,mongodb2.example.net:27017" )
```
- To add a shard for a standalone mongod on port 27017 of mongodb0.example.net, issue the following command:
  sh.addShard( "mongodb0.example.net:27017" )
Note

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

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