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Cassandra Topology Volume Expansion

This guide will show you how to use KubeDB Ops-manager operator to expand the volume of a 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.
You must have a StorageClass that supports volume expansion.
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: The yaml files used in this tutorial are stored in docs/examples/cassandra folder in GitHub repository kubedb/docs.

Expand Volume of Topology Cassandra Cluster

Here, we are going to deploy a Cassandra topology using a supported version by KubeDB operator. Then we are going to apply CassandraOpsRequest to expand its volume.

Prepare Cassandra Topology Cluster

At first verify that your cluster has a storage class, that supports volume expansion. Let’s check,

$ kubectl get storageclass
NAME                   PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
local-path (default)   rancher.io/local-path   Delete          WaitForFirstConsumer   false                  5d22h
longhorn (default)     driver.longhorn.io      Delete          Immediate              true                   6s
longhorn-static        driver.longhorn.io      Delete          Immediate              true                   3s

We can see from the output the standard storage class has ALLOWVOLUMEEXPANSION field as true. So, this storage class supports volume expansion. We can use it.

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

Deploy Cassandra

In this section, we are going to deploy a Cassandra topology cluster for broker and controller with 1GB volume. Then, in the next section we will expand its volume to 2GB 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
        storage:
          storageClassName:
            longhorn
          accessModes:
            - ReadWriteOnce
          resources:
            requests:
              storage: 1Gi
        storageType: Durable
        podTemplate:
          spec:
            containers:
              - name: cassandra
                resources:
                  limits:
                    memory: 3Gi
                    cpu: 2
                  requests:
                    memory: 1Gi
                    cpu: 1
  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/volume-expansion/cassandra.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   4s
cassandra-prod   kubedb.com/v1alpha2   5.0.3     Provisioning   37s
..
cassandra-prod   kubedb.com/v1alpha2   5.0.3     Ready          2m3s

Let’s check volume size from petset, and from the persistent volume,

$ kubectl get petset -n demo cassandra-prod-rack-r0 -o json | jq '.spec.volumeClaimTemplates[0].spec.resources.requests.storage'
"1Gi"


$  kubectl get pv -n demo
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                                              STORAGECLASS   VOLUMEATTRIBUTESCLASS   REASON   AGE
pvc-623e4d80-f508-4bb1-a4cb-4ebdbcbd8495   1Gi        RWO            Delete           Bound    demo/data-cassandra-prod-rack-r0-0                 longhorn       <unset>                          82s
pvc-76b5a0a7-d234-426c-a4cc-ec740d6456ba   1Gi        RWO            Delete           Bound    demo/data-cassandra-prod-rack-r0-1                 longhorn       <unset>                          64s
pvc-84588238-9fea-4ac3-9cfa-f7b04640697c   1Gi        RWO            Delete           Bound    demo/nodetool-cassandra-prod-rack-r0-0             longhorn       <unset>                          82s
pvc-849d404c-d078-4802-a28f-6834d8c81998   1Gi        RWO            Delete           Bound    demo/nodetool-cassandra-prod-rack-r0-1             longhorn       <unset>                          64s
pvc-85a6902d-a596-45db-94f9-1ce355600323   1Gi        RWO            Delete           Bound    demo/main-config-volume-cassandra-prod-rack-r0-1   longhorn       <unset>                          64s
pvc-88d6586e-b502-481d-91fc-dd6381d9b1c0   1Gi        RWO            Delete           Bound    demo/main-config-volume-cassandra-prod-rack-r0-0   longhorn       <unset>                          82s

You can see the petsets have 1GB storage, and the capacity of all the persistent volumes are also 1GB.

We are now ready to apply the CassandraOpsRequest CR to expand the volume of this database.

Volume Expansion

Here, we are going to expand the volume of the cassandra topology cluster.

Create CassandraOpsRequest

In order to expand the volume of the database, we have to create a CassandraOpsRequest CR with our desired volume size. Below is the YAML of the CassandraOpsRequest CR that we are going to create,

apiVersion: ops.kubedb.com/v1alpha1
kind: CassandraOpsRequest
metadata:
  name: cas-volume-expansion
  namespace: demo
spec:
  type: VolumeExpansion
  databaseRef:
    name: cassandra-prod
  volumeExpansion:
    node: 2Gi
    mode: Online

Here,

spec.databaseRef.name specifies that we are performing volume expansion operation on cassandra-prod.
spec.type specifies that we are performing VolumeExpansion on our database.
spec.volumeExpansion.broker specifies the desired volume size for broker node.
spec.volumeExpansion.controller specifies the desired volume size for controller node.

If you want to expand the volume of only one node, you can specify the desired volume size for that node only.

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/volume-expansion/cassandra-volume-expansion-opsreq.yaml
cassandraopsrequest.ops.kubedb.com/cas-volume-expansion created

Verify Cassandra Topology volume expanded successfully

If everything goes well, KubeDB Ops-manager operator will update the volume size of Cassandra object and related PetSets and Persistent Volumes.

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

$ kubectl get cassandraopsrequest -n demo
NAME                   TYPE              STATUS       AGE
cas-volume-expansion   VolumeExpansion   Successful   5m49s

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 expand the volume of cassandra.

$ kubectl describe cassandraopsrequest -n demo cas-volume-expansion
Name:         cas-volume-expansion
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         CassandraOpsRequest
Metadata:
  Creation Timestamp:  2025-07-29T10:07:19Z
  Generation:          1
  Resource Version:    306444
  UID:                 ccc1253b-b69f-4242-a270-fd36c2a15daa
Spec:
  Apply:  IfReady
  Database Ref:
    Name:  cassandra-prod
  Type:    VolumeExpansion
  Volume Expansion:
    Mode:  Online
    Node:  2Gi
Status:
  Conditions:
    Last Transition Time:  2025-07-29T10:08:29Z
    Message:               Cassandra ops-request has started to expand volume of cassandra nodes.
    Observed Generation:   1
    Reason:                VolumeExpansion
    Status:                True
    Type:                  VolumeExpansion
    Last Transition Time:  2025-07-29T10:08:56Z
    Message:               successfully deleted the petSets with orphan propagation policy
    Observed Generation:   1
    Reason:                OrphanPetSetPods
    Status:                True
    Type:                  OrphanPetSetPods
    Last Transition Time:  2025-07-29T10:08:46Z
    Message:               get petset; ConditionStatus:True
    Observed Generation:   1
    Status:                True
    Type:                  GetPetset
    Last Transition Time:  2025-07-29T10:08:46Z
    Message:               delete petset; ConditionStatus:True
    Observed Generation:   1
    Status:                True
    Type:                  DeletePetset
    Last Transition Time:  2025-07-29T10:10:56Z
    Message:               successfully updated PVC sizes
    Observed Generation:   1
    Reason:                UpdateNodePVCs
    Status:                True
    Type:                  UpdateNodePVCs
    Last Transition Time:  2025-07-29T10:09:01Z
    Message:               get pvc; ConditionStatus:True
    Observed Generation:   1
    Status:                True
    Type:                  GetPvc
    Last Transition Time:  2025-07-29T10:09:01Z
    Message:               patch pvc; ConditionStatus:True
    Observed Generation:   1
    Status:                True
    Type:                  PatchPvc
    Last Transition Time:  2025-07-29T10:10:51Z
    Message:               compare storage; ConditionStatus:True
    Observed Generation:   1
    Status:                True
    Type:                  CompareStorage
    Last Transition Time:  2025-07-29T10:11:09Z
    Message:               successfully reconciled the Cassandra resources
    Observed Generation:   1
    Reason:                UpdatePetSets
    Status:                True
    Type:                  UpdatePetSets
    Last Transition Time:  2025-07-29T10:11:19Z
    Message:               PetSet is recreated
    Observed Generation:   1
    Reason:                ReadyPetSets
    Status:                True
    Type:                  ReadyPetSets
    Last Transition Time:  2025-07-29T10:11:14Z
    Message:               get pet set; ConditionStatus:True
    Observed Generation:   1
    Status:                True
    Type:                  GetPetSet
    Last Transition Time:  2025-07-29T10:11:14Z
    Message:               Successfully completed volumeExpansion for Cassandra
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type     Reason                                  Age    From                         Message
  ----     ------                                  ----   ----                         -------
  Normal   Starting                                7m56s  KubeDB Ops-manager Operator  Start processing for CassandraOpsRequest: demo/cas-volume-expansion
  Normal   Starting                                7m56s  KubeDB Ops-manager Operator  Pausing Cassandra databse: demo/cassandra-prod
  Normal   Successful                              7m56s  KubeDB Ops-manager Operator  Successfully paused Cassandra database: demo/cassandra-prod for CassandraOpsRequest: cas-volume-expansion
  Warning  get petset; ConditionStatus:True        7m39s  KubeDB Ops-manager Operator  get petset; ConditionStatus:True
  Warning  delete petset; ConditionStatus:True     7m39s  KubeDB Ops-manager Operator  delete petset; ConditionStatus:True
  Warning  get petset; ConditionStatus:True        7m34s  KubeDB Ops-manager Operator  get petset; ConditionStatus:True
  Normal   OrphanPetSetPods                        7m29s  KubeDB Ops-manager Operator  successfully deleted the petSets with orphan propagation policy
  Warning  get pvc; ConditionStatus:True           7m24s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  patch pvc; ConditionStatus:True         7m24s  KubeDB Ops-manager Operator  patch pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           7m19s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  compare storage; ConditionStatus:False  7m19s  KubeDB Ops-manager Operator  compare storage; ConditionStatus:False
  Warning  get pvc; ConditionStatus:True           7m14s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           7m9s   KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           7m4s   KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           6m59s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           6m54s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           6m49s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           6m44s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           6m39s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           6m34s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           6m29s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           6m24s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  compare storage; ConditionStatus:True   6m24s  KubeDB Ops-manager Operator  compare storage; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           6m19s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  patch pvc; ConditionStatus:True         6m19s  KubeDB Ops-manager Operator  patch pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           6m14s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  compare storage; ConditionStatus:False  6m14s  KubeDB Ops-manager Operator  compare storage; ConditionStatus:False
  Warning  get pvc; ConditionStatus:True           6m9s   KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           6m4s   KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           5m59s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           5m54s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           5m49s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           5m44s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           5m39s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  get pvc; ConditionStatus:True           5m34s  KubeDB Ops-manager Operator  get pvc; ConditionStatus:True
  Warning  compare storage; ConditionStatus:True   5m34s  KubeDB Ops-manager Operator  compare storage; ConditionStatus:True
  Normal   UpdateNodePVCs                          5m29s  KubeDB Ops-manager Operator  successfully updated PVC sizes
  Normal   UpdatePetSets                           5m16s  KubeDB Ops-manager Operator  successfully reconciled the Cassandra resources
  Normal   UpdatePetSets                           5m13s  KubeDB Ops-manager Operator  successfully reconciled the Cassandra resources
  Warning  get pet set; ConditionStatus:True       5m11s  KubeDB Ops-manager Operator  get pet set; ConditionStatus:True
  Normal   ReadyPetSets                            5m11s  KubeDB Ops-manager Operator  PetSet is recreated
  Normal   Starting                                5m11s  KubeDB Ops-manager Operator  Resuming Cassandra database: demo/cassandra-prod
  Normal   Successful                              5m11s  KubeDB Ops-manager Operator  Successfully resumed Cassandra database: demo/cassandra-prod for CassandraOpsRequest: cas-volume-expansion
  Normal   Starting                                5m11s  KubeDB Ops-manager Operator  Pausing Cassandra databse: demo/cassandra-prod
  Normal   Successful                              5m11s  KubeDB Ops-manager Operator  Successfully paused Cassandra database: demo/cassandra-prod for CassandraOpsRequest: cas-volume-expansion
  Warning  get pet set; ConditionStatus:True       5m6s   KubeDB Ops-manager Operator  get pet set; ConditionStatus:True
  Normal   ReadyPetSets                            5m6s   KubeDB Ops-manager Operator  PetSet is recreated

Now, we are going to verify from the Petset, and the Persistent Volumes whether the volume of the database has expanded to meet the desired state, Let’s check,

$ kubectl get petset -n demo cassandra-prod-rack-r0 -o json | jq '.spec.volumeClaimTemplates[0].spec.resources.requests.storage'
"2Gi"


$  kubectl get pv -n demo 
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                                              STORAGECLASS   VOLUMEATTRIBUTESCLASS   REASON   AGE
pvc-7efa007f-5fb2-4e64-aea0-233ec456703f   1Gi        RWO            Delete           Bound    demo/main-config-volume-cassandra-prod-rack-r0-1   longhorn       <unset>                          11m
pvc-88f8ec55-ae5b-48dd-9b3a-0dc113cdaa43   2Gi        RWO            Delete           Bound    demo/data-cassandra-prod-rack-r0-1                 longhorn       <unset>                          11m
pvc-c455344e-0f17-42d2-8fd9-062fa2f1b0a1   1Gi        RWO            Delete           Bound    demo/main-config-volume-cassandra-prod-rack-r0-0   longhorn       <unset>                          11m
pvc-d19d62ac-b37b-406e-a7d6-a10f4f74d929   2Gi        RWO            Delete           Bound    demo/data-cassandra-prod-rack-r0-0                 longhorn       <unset>                          11m
pvc-df152a7a-12ea-4690-b64e-ccb2decce8cd   1Gi        RWO            Delete           Bound    demo/nodetool-cassandra-prod-rack-r0-1             longhorn       <unset>                          11m
pvc-f8420d54-05f8-4ea2-b70c-11a3737e04e4   1Gi        RWO            Delete           Bound    demo/nodetool-cassandra-prod-rack-r0-0             longhorn       <unset>                          11m

The above output verifies that we have successfully expanded the data related volume of the Cassandra.

Cleaning Up

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

kubectl delete cassandraopsrequest -n demo cas-volume-expansion
kubectl delete cas -n demo cassandra-prod
kubectl delete ns demo

Next Steps

Detail concepts of Cassandra object.
Monitor your Cassandra database with KubeDB using out-of-the-box Prometheus operator.

Want to hack on KubeDB? Check our contribution guidelines.

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