# Scale Percona Server for MongoDB on Kubernetes and OpenShift

One of the great advantages brought by Kubernetes and the OpenShift platform is
the ease of an application scaling. Scaling a Deployment up or down ensures new
Pods are created and set to available Kubernetes nodes.

The size of the cluster is controlled by the `size` key in the
[Custom Resource options](operator.md#operator-custom-resource-options)
configuration.

!!! note

    The Operator will not allow to scale Percona Server for MongoDB with the
    `kubectl scale statefulset <StatefulSet name>` command as it puts `size`
    configuration options out of sync.

You can change size separately for different components of your cluster by
setting this option in the appropriate subsections:


* [replsets.size](operator.md#replsets-size) allows to set the size of the
    MongoDB Replica Set,
* [replsets.arbiter.size](operator.md#replsets-arbiter-size) allows to set the
    number of [Replica Set Arbiter instances](arbiter.md#arbiter),
* [sharding.configsvrReplSet.size](operator.md#sharding-configsvrreplset-size)
    allows to set the number of [Config Server instances](https://docs.mongodb.com/manual/core/sharded-cluster-config-servers/),
* [sharding.mongos.size](operator.md#sharding-mongos-size) allows to set the
    number of [mongos](https://docs.mongodb.com/manual/core/sharded-cluster-query-router/)
    instances.

For example, the following update in `deploy/cr.yaml` will set the size of the
MongoDB Replica Set to `5` nodes:

```yaml
....
replsets:
  ....
  size: 5
  ....
```

Don’t forget to apply changes as usual, running the
`kubectl apply -f deploy/cr.yaml` command.