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New to KubeDB? Please start here.

Horizontal Scale Cassandra Topology Cluster

This guide will show you how to use KubeDB Ops-manager operator to scale the Cassandra topology cluster.

Before You Begin

  • At first, you need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using kind.

  • Install KubeDB Provisioner and Ops-manager operator in your cluster following the steps here.

  • You should be familiar with the following KubeDB concepts:

To keep everything isolated, we are going to use a separate namespace called demo throughout this tutorial.

$ kubectl create ns demo
namespace/demo created

Note: YAML files used in this tutorial are stored in docs/examples/cassandra directory of kubedb/docs repository.

Apply Horizontal Scaling on Topology Cluster

Here, we are going to deploy a Cassandra topology cluster using a supported version by KubeDB operator. Then we are going to apply horizontal scaling on it.

Prepare Cassandra Topology cluster

Now, we are going to deploy a Cassandra topology cluster with version 5.0.3.

Deploy Cassandra topology cluster

In this section, we are going to deploy a Cassandra topology cluster. Then, in the next section we will scale the cluster using CassandraOpsRequest CRD. Below is the YAML of the Cassandra CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: Cassandra
metadata:
  name: cassandra-prod
  namespace: demo
spec:
  version: 5.0.3
  topology:
    rack:
      - name: r0
        replicas: 2
        podTemplate:
          spec:
            containers:
              - name: cassandra
                resources:
                  limits:
                    memory: 2Gi
                    cpu: 2
                  requests:
                    memory: 1Gi
                    cpu: 1
        storage:
          accessModes:
            - ReadWriteOnce
          resources:
            requests:
              storage: 1Gi
        storageType: Durable
  deletionPolicy: WipeOut

Let’s create the Cassandra CR we have shown above,

$ kubectl create -f https://github.com/kubedb/docs/raw/v2025.7.31/docs/examples/cassandra/scaling/cassandra-topology.yaml
cassandra.kubedb.com/cassandra-prod created

Now, wait until cassandra-prod has status Ready. i.e,

$kubectl get cas -n demo -w
NAME             TYPE                  VERSION   STATUS         AGE
cassandra-prod   kubedb.com/v1alpha2   5.0.3     Provisioning   27s
cassandra-prod   kubedb.com/v1alpha2   5.0.3     Provisioning   1m27s
.
.
cassandra-prod   kubedb.com/v1alpha2   5.0.3     Ready          2m27s

Let’s check the number of replicas has from cassandra object, number of pods the petset have,

$ kubectl get petset -n demo cassandra-prod-rack-r0 -o json | jq '.spec.replicas'
2

We can see from commands that the cluster has 2 replicas for rack r0 as we have defined in the yaml.

We are now ready to apply the CassandraOpsRequest CR to scale this cluster.

Scale Up Replicas

Here, we are going to scale up the replicas of the topology cluster to meet the desired number of replicas after scaling.

Create CassandraOpsRequest

In order to scale up the replicas of the topology cluster, we have to create a CassandraOpsRequest CR with our desired replicas. Below is the YAML of the CassandraOpsRequest CR that we are going to create,

apiVersion: ops.kubedb.com/v1alpha1
kind: CassandraOpsRequest
metadata:
  name: cassandra-horizontal-scale-up
  namespace: demo
spec:
  type: HorizontalScaling
  databaseRef:
    name: cassandra-prod
  horizontalScaling:
    node: 4

Here,

  • spec.databaseRef.name specifies that we are performing horizontal scaling operation on cassandra-prod cluster.
  • spec.type specifies that we are performing HorizontalScaling on cassandra.
  • spec.horizontalScaling.node specifies the desired replicas after scaling for cassandra cluster.

Let’s create the CassandraOpsRequest CR we have shown above,

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2025.7.31/docs/examples/cassandra/scaling/horizontal-scaling/cassandra-hscale-up-topology.yaml
cassandraopsrequest.ops.kubedb.com/casops-hscale-up-topology created

Verify Topology cluster replicas scaled up successfully

If everything goes well, KubeDB Ops-manager operator will update the replicas of Cassandra object and related PetSets and Pods.

Let’s wait for CassandraOpsRequest to be Successful. Run the following command to watch CassandraOpsRequest CR,

$ watch kubectl get cassandraopsrequest -n demo
NAME                             TYPE                STATUS       AGE
cassandra-horizontal-scale-up    HorizontalScaling   Successful   106s

We can see from the above output that the CassandraOpsRequest has succeeded. If we describe the CassandraOpsRequest we will get an overview of the steps that were followed to scale the cluster.

$ kubectl describe cassandraopsrequests -n demo cassandra-horizontal-scale-up 
kubectl describe cassandraopsrequests -n demo cassandra-horizontal-scale-up
Name:         cassandra-horizontal-scale-up
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         CassandraOpsRequest
Metadata:
  Creation Timestamp:  2025-07-18T05:48:27Z
  Generation:          1
  Resource Version:    2808
  UID:                 705dd54c-dc75-4a1f-bbbb-bc1b6028c611
Spec:
  Apply:  IfReady
  Database Ref:
    Name:  cassandra-prod
  Horizontal Scaling:
    Node:  4
  Type:    HorizontalScaling
Status:
  Conditions:
    Last Transition Time:  2025-07-18T05:49:37Z
    Message:               Cassandra ops-request has started to horizontally scaling the nodes
    Observed Generation:   1
    Reason:                HorizontalScaling
    Status:                True
    Type:                  HorizontalScaling
    Last Transition Time:  2025-07-18T05:49:55Z
    Message:               Successfully Scaled Up Node
    Observed Generation:   1
    Reason:                HorizontalScaleUp
    Status:                True
    Type:                  HorizontalScaleUp
    Last Transition Time:  2025-07-18T05:49:45Z
    Message:               patch petset; ConditionStatus:True
    Observed Generation:   1
    Status:                True
    Type:                  PatchPetset
    Last Transition Time:  2025-07-18T05:50:04Z
    Message:               successfully reconciled the Cassandra with modified node
    Observed Generation:   1
    Reason:                UpdatePetSets
    Status:                True
    Type:                  UpdatePetSets
    Last Transition Time:  2025-07-18T05:50:04Z
    Message:               Successfully completed horizontally scale Cassandra cluster
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type     Reason                              Age   From                         Message
  ----     ------                              ----  ----                         -------
  Normal   Starting                            39s   KubeDB Ops-manager Operator  Start processing for CassandraOpsRequest: demo/cassandra-horizontal-scale-up
  Normal   Starting                            39s   KubeDB Ops-manager Operator  Pausing Cassandra databse: demo/cassandra-prod
  Normal   Successful                          39s   KubeDB Ops-manager Operator  Successfully paused Cassandra database: demo/cassandra-prod for CassandraOpsRequest: cassandra-horizontal-scale-up
  Warning  patch petset; ConditionStatus:True  31s   KubeDB Ops-manager Operator  patch petset; ConditionStatus:True
  Warning  patch petset; ConditionStatus:True  26s   KubeDB Ops-manager Operator  patch petset; ConditionStatus:True
  Normal   HorizontalScaleUp                   21s   KubeDB Ops-manager Operator  Successfully Scaled Up Node
  Normal   UpdatePetSets                       12s   KubeDB Ops-manager Operator  successfully reconciled the Cassandra with modified node
  Normal   Starting                            12s   KubeDB Ops-manager Operator  Resuming Cassandra database: demo/cassandra-prod
  Normal   Successful                          12s   KubeDB Ops-manager Operator  Successfully resumed Cassandra database: demo/cassandra-prod for CassandraOpsRequest: cassandra-horizontal-scale-up

Now, we are going to verify the number of replicas this cluster has from the Cassandra object, number of pods the petset have,

$ kubectl get petset -n demo cassandra-prod-rack-r0 -o json | jq '.spec.replicas'
4

Scale Down Replicas

Here, we are going to scale down the replicas of the cassandra topology cluster to meet the desired number of replicas after scaling.

Create CassandraOpsRequest

In order to scale down the replicas of the cassandra topology cluster, we have to create a CassandraOpsRequest CR with our desired replicas. Below is the YAML of the CassandraOpsRequest CR that we are going to create,

apiVersion: ops.kubedb.com/v1alpha1
kind: CassandraOpsRequest
metadata:
  name: cassandra-horizontal-scale-down
  namespace: demo
spec:
  type: HorizontalScaling
  databaseRef:
    name: cassandra-prod
  horizontalScaling:
    node: 2

Here,

  • spec.databaseRef.name specifies that we are performing horizontal scaling down operation on cassandra-prod cluster.
  • spec.type specifies that we are performing HorizontalScaling on cassandra.
  • spec.horizontalScaling.topology.node specifies the desired replicas after scaling for the cassandra nodes.

Let’s create the CassandraOpsRequest CR we have shown above,

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2025.7.31/docs/examples/cassandra/scaling/horizontal-scaling/cassandra-hscale-down-topology.yaml
cassandraopsrequest.ops.kubedb.com/casops-hscale-down-topology created

Verify Topology cluster replicas scaled down successfully

If everything goes well, KubeDB Ops-manager operator will update the replicas of Cassandra object and related PetSets and Pods.

Let’s wait for CassandraOpsRequest to be Successful. Run the following command to watch CassandraOpsRequest CR,

$ watch kubectl get cassandraopsrequest -n demo
NAME                              TYPE                STATUS       AGE
cassandra-horizontal-scale-down   HorizontalScaling   Successful   62s

We can see from the above output that the CassandraOpsRequest has succeeded. If we describe the CassandraOpsRequest we will get an overview of the steps that were followed to scale the cluster.

$ kubectl describe cassandraopsrequests -n demo cassandra-horizontal-scale-down
Name:         cassandra-horizontal-scale-down
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         CassandraOpsRequest
Metadata:
  Creation Timestamp:  2025-07-18T05:53:38Z
  Generation:          1
  Resource Version:    2937
  UID:                 073b5918-d0c5-4a0a-9d17-3927220a727b
Spec:
  Apply:  IfReady
  Database Ref:
    Name:  cassandra-prod
  Horizontal Scaling:
    Node:  2
  Type:    HorizontalScaling
Status:
  Conditions:
    Last Transition Time:  2025-07-18T05:53:38Z
    Message:               Cassandra ops-request has started to horizontally scaling the nodes
    Observed Generation:   1
    Reason:                HorizontalScaling
    Status:                True
    Type:                  HorizontalScaling
    Last Transition Time:  2025-07-18T05:53:56Z
    Message:               Successfully Scaled Down Node
    Observed Generation:   1
    Reason:                HorizontalScaleDown
    Status:                True
    Type:                  HorizontalScaleDown
    Last Transition Time:  2025-07-18T05:53:46Z
    Message:               patch petset; ConditionStatus:True
    Observed Generation:   1
    Status:                True
    Type:                  PatchPetset
    Last Transition Time:  2025-07-18T05:54:05Z
    Message:               successfully reconciled the Cassandra with modified node
    Observed Generation:   1
    Reason:                UpdatePetSets
    Status:                True
    Type:                  UpdatePetSets
    Last Transition Time:  2025-07-18T05:54:05Z
    Message:               Successfully completed horizontally scale Cassandra cluster
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type     Reason                              Age    From                         Message
  ----     ------                              ----   ----                         -------
  Normal   Starting                            2m21s  KubeDB Ops-manager Operator  Start processing for CassandraOpsRequest: demo/cassandra-horizontal-scale-down
  Normal   Starting                            2m21s  KubeDB Ops-manager Operator  Pausing Cassandra databse: demo/cassandra-prod
  Normal   Successful                          2m21s  KubeDB Ops-manager Operator  Successfully paused Cassandra database: demo/cassandra-prod for CassandraOpsRequest: cassandra-horizontal-scale-down
  Warning  patch petset; ConditionStatus:True  2m13s  KubeDB Ops-manager Operator  patch petset; ConditionStatus:True
  Warning  patch petset; ConditionStatus:True  2m8s   KubeDB Ops-manager Operator  patch petset; ConditionStatus:True
  Normal   HorizontalScaleDown                 2m3s   KubeDB Ops-manager Operator  Successfully Scaled Down Node
  Normal   UpdatePetSets                       114s   KubeDB Ops-manager Operator  successfully reconciled the Cassandra with modified node
  Normal   Starting                            114s   KubeDB Ops-manager Operator  Resuming Cassandra database: demo/cassandra-prod
  Normal   Successful                          114s   KubeDB Ops-manager Operator  Successfully resumed Cassandra database: demo/cassandra-prod for CassandraOpsRequest: cassandra-horizontal-scale-down

Now, we are going to verify the number of replicas this cluster has from the number of pods the petset have,

Broker Replicas

$
$ kubectl get petset -n demo cassandra-prod-rack-r0 -o json | jq '.spec.replicas'
2

From all the above outputs we can see that the replicas of the topology cluster is 2. That means we have successfully scaled down the replicas of the Cassandra topology cluster.

Cleaning Up

To clean up the Kubernetes resources created by this tutorial, run:

kubectl delete cas -n demo cassandra-prod
kubectl delete cassandraopsrequest -n demo  cassandra-horizontal-scale-up  cassandra-horizontal-scale-down
kubectl delete ns demo

Next Steps

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