Charmed MongoDB K8s Tutorials > Deploy a sharded cluster > 4. Add and remove shards
Add and remove shards
Shards spread data evenly throughout the cluster, making a database highly available. This part of the tutorial will teach you how to scale your cluster by adding and removing shards.
Disclaimer: This tutorial hosts all shards on the same machine. This should never be done in a production environment.
To enable high availability in a production environment, replicas should be hosted on different servers to maintain isolation.
Add shards
Sharded clusters cannot be scaled via juju the way replica sets can. So, before adding a shard to the cluster, we need to create it.
To create a new shard, deploy a Charmed MongoDB K8s application with the shard config option role:
juju deploy mongodb-k8s --config role="shard" shard2
Use juju status --watch 1s --relations to wait until shard2 is blocked due to missing relation.
Now that our shard is deployed, it is ready to be added to the cluster. For the shard to be added to the cluster it must be integrated with the config-server:
juju integrate config-server:config-server shard2:sharding
To verify that the shard is present in the cluster, we can check the cluster configuration through the mongos router inside config-server and listing shards like we did in 4. Access a sharded cluster.
Remove shards
To remove a shard from Charmed MongoDB, we remove the integration from the shard and the config-server. This signals to the cluster that it is time to drain the shard and remove it from the config.
First, break the integration:
juju remove-relation config-server:config-server shard2:sharding
Watch juju status --watch 1s --relations until shard2 has finished being drained from the cluster and is no longer listed as a requirer of the config-server integration provider.
Now that the shard has been drained and removed from the configuration, it is safe to remove it altogether. To do so, run:
juju remove-application shard2
Watch the cluster with juju status --watch 1s --relations until shard2 is no longer listed anywhere.
Next Step: 5. Manage passwords