New to KubeDB? Please start here.

Autoscaling the Compute Resource of a Cassandra

This guide will show you how to use KubeDB to autoscaling compute resources i.e. cpu and memory of a Cassandra.

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.
Install KubeDB Provisioner, Ops-manager and Autoscaler operator in your cluster following the steps here.
Install Metrics Server from 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.

Autoscaling of Cassandra

In this section, we are going to deploy a Cassandra with version 5.0.3 Then, in the next section we will set up autoscaling for this Cassandra using CassandraAutoscaler CRD. Below is the YAML of the Cassandra CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: Cassandra
metadata:
  name: cassandra-autoscale
  namespace: demo
spec:
  version: "5.0.3"
  topology:
    rack:
      - name: r0
        replicas: 2
        storage:
          accessModes:
            - ReadWriteOnce
          resources:
            requests:
              storage: 600Mi
        podTemplate:
          spec:
            containers:
              - name: cassandra
                resources:
                  limits:
                    memory: 2Gi
                    cpu: 1000m
                  requests:
                    memory: 600Mi
                    cpu: 500m
  deletionPolicy: WipeOut

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

$ kubectl create -f https://github.com/kubedb/docs/raw/v2025.7.31/docs/examples/cassandra/autoscaling/compute/cassandra-autoscale.yaml
cassandra.kubedb.com/cassandra-autoscale created

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

$ kubectl get cas -n demo
NAME                 TYPE                  VERSION   STATUS   AGE
cassandra-autoscale   kubedb.com/v1alpha2   5.0.3     Ready    22s

Let’s check the Pod containers resources,

$ kubectl get pod -n demo cassandra-autoscale-rack-r0-0 -o json | jq '.spec.containers[].resources'
{
  "limits": {
    "cpu": "1",
    "memory": "2Gi"
  },
  "requests": {
    "cpu": "500m",
    "memory": "600Mi"
  }
}

Let’s check the Cassandra resources,

$ kubectl get cassandra -n demo cassandra-autoscale -o json | jq '.spec.topology.rack[0].podTemplate.spec.containers[0].resources'
{
  "limits": {
    "cpu": "1",
    "memory": "2Gi"
  },
  "requests": {
    "cpu": "500m",
    "memory": "600Mi"
  }
}

You can see from the above outputs that the resources are same as the one we have assigned while deploying the cassandra.

We are now ready to apply the CassandraAutoscaler CRO to set up autoscaling for this database.

Compute Resource Autoscaling

Here, we are going to set up compute (cpu and memory) autoscaling using a CassandraAutoscaler Object.

Create CassandraAutoscaler Object

In order to set up compute resource autoscaling for this Cassandra, we have to create a CassandraAutoscaler CRO with our desired configuration. Below is the YAML of the CassandraAutoscaler object that we are going to create,

apiVersion: autoscaling.kubedb.com/v1alpha1
kind: CassandraAutoscaler
metadata:
  name: cassandra-autoscale-ops
  namespace: demo
spec:
  databaseRef:
    name: cassandra-autoscale
  compute:
    cassandra:
      trigger: "On"
      podLifeTimeThreshold: 5m
      resourceDiffPercentage: 20
      minAllowed:
        cpu: 600m
        memory: 1.2Gi
      maxAllowed:
        cpu: 1
        memory: 2Gi
      controlledResources: ["cpu", "memory"]
      containerControlledValues: "RequestsAndLimits"

Here,

spec.databaseRef.name specifies that we are performing compute resource autoscaling on cassandra-autoscale.
spec.compute.cassandra.trigger specifies that compute resource autoscaling is enabled for this cassandra.
spec.compute.cassandra.podLifeTimeThreshold specifies the minimum lifetime for at least one of the pod to initiate a vertical scaling.
spec.compute.cassandra.resourceDiffPercentage specifies the minimum resource difference in percentage. The default is 10%. If the difference between current & recommended resource is less than ResourceDiffPercentage, Autoscaler Operator will ignore the updating.
spec.compute.cassandra.minAllowed specifies the minimum allowed resources for this cassandra.
spec.compute.cassandra.maxAllowed specifies the maximum allowed resources for this cassandra.
spec.compute.cassandra.controlledResources specifies the resources that are controlled by the autoscaler.
spec.compute.cassandra.containerControlledValues specifies which resource values should be controlled. The default is “RequestsAndLimits”.
spec.opsRequestOptions contains the options to pass to the created OpsRequest. It has 2 fields. Know more about them here : timeout, apply.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2025.7.31/docs/examples/cassandra/autoscaling/compute/cassandra-autoscaler-ops.yaml
cassandraautoscaler.autoscaling.kubedb.com/cassandra-autoscaler-ops created

Verify Autoscaling is set up successfully

Let’s check that the cassandraautoscaler resource is created successfully,

$ kubectl get cassandraautoscaler -n demo
NAME                   AGE
cassandra-autoscale-ops   6m55s

$ kubectl describe cassandraautoscaler cassandra-autoscale-ops -n demo
Name:         cassandra-autoscale-ops
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  autoscaling.kubedb.com/v1alpha1
Kind:         CassandraAutoscaler
Metadata:
  Creation Timestamp:  2025-07-14T09:51:36Z
  Generation:          1
  Owner References:
    API Version:           kubedb.com/v1alpha2
    Block Owner Deletion:  true
    Controller:            true
    Kind:                  Cassandra
    Name:                  cassandra-autoscale
    UID:                   4abde3d7-a0f4-4f4e-bcdc-6518444f1e23
  Resource Version:        10064
  UID:                     e29a989b-becd-4812-9ab3-65adead1d578
Spec:
  Compute:
    Cassandra:
      Container Controlled Values:  RequestsAndLimits
      Controlled Resources:
        cpu
        memory
      Max Allowed:
        Cpu:     2
        Memory:  3Gi
      Min Allowed:
        Cpu:                     800m
        Memory:                  2Gi
      Pod Life Time Threshold:   5m0s
      Resource Diff Percentage:  20
      Trigger:                   On
  Database Ref:
    Name:  cassandra-autoscale
  Ops Request Options:
    Apply:  IfReady
Status:
  Checkpoints:
    Cpu Histogram:
      Bucket Weights:
        Index:              1
        Weight:             4631
        Index:              3
        Weight:             10000
        Index:              44
        Weight:             6125
      Reference Timestamp:  2025-07-14T10:10:00Z
      Total Weight:         0.4133802430760871
    First Sample Start:     2025-07-14T10:09:25Z
    Last Sample Start:      2025-07-14T10:11:26Z
    Last Update Time:       2025-07-14T10:11:46Z
    Memory Histogram:
      Reference Timestamp:  2025-07-14T10:15:00Z
    Ref:
      Container Name:     cassandra
      Vpa Object Name:    cassandra-autoscale-rack-r0
    Total Samples Count:  4
    Version:              v3
  Conditions:
    Last Transition Time:  2025-07-14T10:09:46Z
    Message:               Successfully created CassandraOpsRequest demo/casops-cassandra-autoscale-rack-r0-kefyuq
    Observed Generation:   1
    Reason:                CreateOpsRequest
    Status:                True
    Type:                  CreateOpsRequest
  Vpas:
    Conditions:
      Last Transition Time:  2025-07-14T10:09:46Z
      Status:                True
      Type:                  RecommendationProvided
    Recommendation:
      Container Recommendations:
        Container Name:  cassandra
        Lower Bound:
          Cpu:     800m
          Memory:  2Gi
        Target:
          Cpu:     1836m
          Memory:  2Gi
        Uncapped Target:
          Cpu:     1836m
          Memory:  1168723596
        Upper Bound:
          Cpu:     2
          Memory:  3Gi
    Vpa Name:      cassandra-autoscale-rack-r0
Events:            <none>

So, the Cassandraautoscaler resource is created successfully.

you can see in the Status.VPAs.Recommendation section, that recommendation has been generated for our Cassandra. Our autoscaler operator continuously watches the recommendation generated and creates an cassandraopsrequest based on the recommendations, if the cassandra pods are needed to scaled up or down.

Let’s watch the cassandraopsrequest in the demo namespace to see if any cassandraopsrequest object is created. After some time you’ll see that a cassandraopsrequest will be created based on the recommendation.

$ watch kubectl get cassandraopsrequest -n demo
Every 2.0s: kubectl get cassandraopsrequest -n demo
NAME                                        TYPE              STATUS        AGE
casops-cassandra-autoscale-rack-r0-kefyuq   VerticalScaling   Progressing   1m28s

Let’s wait for the ops request to become successful.

$ watch kubectl get cassandraopsrequest -n demo
Every 2.0s: kubectl get cassandraopsrequest -n demo
NAME                                        TYPE              STATUS       AGE
casops-cassandra-autoscale-rack-r0-kefyuq   VerticalScaling   Successful   3m34s

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 Cassandra.

$ kubectl describe cassandraopsrequest -n demo casops-cassandra-autoscale-rack-r0-kefyuq
Name:         casops-cassandra-autoscale-rack-r0-kefyuq
Namespace:    demo
Labels:       app.kubernetes.io/component=database
              app.kubernetes.io/instance=cassandra-autoscale
              app.kubernetes.io/managed-by=kubedb.com
              app.kubernetes.io/name=cassandras.kubedb.com
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         CassandraOpsRequest
Metadata:
  Creation Timestamp:  2025-07-14T10:09:46Z
  Generation:          1
  Owner References:
    API Version:           autoscaling.kubedb.com/v1alpha1
    Block Owner Deletion:  true
    Controller:            true
    Kind:                  CassandraAutoscaler
    Name:                  cassandra-autoscale-ops
    UID:                   e29a989b-becd-4812-9ab3-65adead1d578
  Resource Version:        10149
  UID:                     e55a25aa-c629-48a8-a6d6-ff7df56edf2d
Spec:
  Apply:  IfReady
  Database Ref:
    Name:  cassandra-autoscale
  Type:    VerticalScaling
  Vertical Scaling:
    Node:
      Resources:
        Limits:
          Cpu:     1600m
          Memory:  7330077518
        Requests:
          Cpu:     800m
          Memory:  2Gi
Status:
  Conditions:
    Last Transition Time:  2025-07-14T10:09:46Z
    Message:               Cassandra ops-request has started to vertically scaling the Cassandra nodes
    Observed Generation:   1
    Reason:                VerticalScaling
    Status:                True
    Type:                  VerticalScaling
    Last Transition Time:  2025-07-14T10:09:49Z
    Message:               Successfully updated PetSets Resources
    Observed Generation:   1
    Reason:                UpdatePetSets
    Status:                True
    Type:                  UpdatePetSets
    Last Transition Time:  2025-07-14T10:12:34Z
    Message:               Successfully Restarted Pods With Resources
    Observed Generation:   1
    Reason:                RestartPods
    Status:                True
    Type:                  RestartPods
    Last Transition Time:  2025-07-14T10:09:54Z
    Message:               get pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-0
    Observed Generation:   1
    Status:                True
    Type:                  GetPod--cassandra-autoscale-rack-r0-0
    Last Transition Time:  2025-07-14T10:09:54Z
    Message:               evict pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-0
    Observed Generation:   1
    Status:                True
    Type:                  EvictPod--cassandra-autoscale-rack-r0-0
    Last Transition Time:  2025-07-14T10:09:59Z
    Message:               running pod; ConditionStatus:False
    Observed Generation:   1
    Status:                False
    Type:                  RunningPod
    Last Transition Time:  2025-07-14T10:10:34Z
    Message:               get pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-1
    Observed Generation:   1
    Status:                True
    Type:                  GetPod--cassandra-autoscale-rack-r0-1
    Last Transition Time:  2025-07-14T10:10:34Z
    Message:               evict pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-1
    Observed Generation:   1
    Status:                True
    Type:                  EvictPod--cassandra-autoscale-rack-r0-1
    Last Transition Time:  2025-07-14T10:12:34Z
    Message:               Successfully completed the vertical scaling for Cassandra
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type     Reason                                                                  Age    From                         Message
  ----     ------                                                                  ----   ----                         -------
  Normal   Starting                                                                4m17s  KubeDB Ops-manager Operator  Start processing for CassandraOpsRequest: demo/casops-cassandra-autoscale-rack-r0-kefyuq
  Normal   Starting                                                                4m17s  KubeDB Ops-manager Operator  Pausing Cassandra databse: demo/cassandra-autoscale
  Normal   Successful                                                              4m17s  KubeDB Ops-manager Operator  Successfully paused Cassandra database: demo/cassandra-autoscale for CassandraOpsRequest: casops-cassandra-autoscale-rack-r0-kefyuq
  Normal   UpdatePetSets                                                           4m14s  KubeDB Ops-manager Operator  Successfully updated PetSets Resources
  Warning  get pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-0    4m9s   KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-0
  Warning  evict pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-0  4m9s   KubeDB Ops-manager Operator  evict pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-0
  Warning  running pod; ConditionStatus:False                                      4m4s   KubeDB Ops-manager Operator  running pod; ConditionStatus:False
  Warning  get pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-1    3m29s  KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-1
  Warning  evict pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-1  3m29s  KubeDB Ops-manager Operator  evict pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-1
  Warning  get pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-0    2m49s  KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-0
  Warning  evict pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-0  2m49s  KubeDB Ops-manager Operator  evict pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-0
  Warning  get pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-1    2m9s   KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-1
  Warning  evict pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-1  2m9s   KubeDB Ops-manager Operator  evict pod; ConditionStatus:True; PodName:cassandra-autoscale-rack-r0-1
  Normal   RestartPods                                                             89s    KubeDB Ops-manager Operator  Successfully Restarted Pods With Resources
  Normal   Starting                                                                89s    KubeDB Ops-manager Operator  Resuming Cassandra database: demo/cassandra-autoscale
  Normal   Successful                                                              89s    KubeDB Ops-manager Operator  Successfully resumed Cassandra database: demo/cassandra-autoscale for CassandraOpsRequest: casops-cassandra-autoscale-rack-r0-kefyuq

Now, we are going to verify from the Pod, and the Cassandra yaml whether the resources of the Cassandra has updated to meet up the desired state, Let’s check,

$  kubectl get pod -n demo cassandra-autoscale-rack-r0-0 -o json | jq '.spec.containers[].resources'
{
  "limits": {
    "cpu": "1600m",
    "memory": "7330077518"
  },
  "requests": {
    "cpu": "800m",
    "memory": "2Gi"
  }
}

$  kubectl get cassandra -n demo cassandra-autoscale -o json | jq '.spec.topology.rack[0].podTemplate.spec.containers[0].resources'
{
  "limits": {
    "cpu": "1",
    "memory": "2Gi"
  },
  "requests": {
    "cpu": "500m",
    "memory": "600Mi"
  }
}

The above output verifies that we have successfully auto-scaled the resources of the cassandra.

Cleaning Up

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

kubectl delete cas -n demo cassandra-autoscale

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