New to KubeDB? Please start here.

Autoscaling the Compute Resource of a ClickHouse

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

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/clickhouse directory of kubedb/docs repository.

Autoscaling of ClickHouse

In this section, we are going to deploy a ClickHouse with version 24.4.1 Then, in the next section we will set up autoscaling for this ClickHouse using ClickHouseAutoscaler CRD. Below is the YAML of the ClickHouse CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: ClickHouse
metadata:
  name: clickhouse-prod
  namespace: demo
spec:
  version: 24.4.1
  clusterTopology:
    clickHouseKeeper:
      externallyManaged: false
      spec:
        replicas: 3
        storage:
          accessModes:
            - ReadWriteOnce
          resources:
            requests:
              storage: 1Gi
    cluster:
      name: appscode-cluster
      shards: 2
      replicas: 2
      podTemplate:
        spec:
          containers:
            - name: clickhouse
              resources:
                limits:
                  memory: 2Gi
                requests:
                  memory: 1Gi
                  cpu: 900m
          initContainers:
            - name: clickhouse-init
              resources:
                limits:
                  memory: 1Gi
                requests:
                  cpu: 500m
                  memory: 1Gi
      storage:
        storageClassName: "longhorn"
        accessModes:
          - ReadWriteOnce
        resources:
          requests:
            storage: 1Gi
  deletionPolicy: WipeOut

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

$ kubectl create -f https://github.com/kubedb/docs/raw/v2025.10.17/docs/examples/clickhouse/autoscaling/compute/clickhouse-autoscale.yaml
clickhouse.kubedb.com/clickhouse-prod created

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

➤ kubectl get ch -n demo clickhouse-prod -w
NAME              TYPE                  VERSION   STATUS         AGE
clickhouse-prod   kubedb.com/v1alpha2   24.4.1    Provisioning   114s
clickhouse-prod   kubedb.com/v1alpha2   24.4.1    Provisioning   117s
.
.
.
clickhouse-prod   kubedb.com/v1alpha2   24.4.1    Ready          2m44s

Let’s check the Pod containers resources,

➤ kubectl get pod -n demo clickhouse-prod-appscode-cluster-shard-0-0 -o json | jq '.spec.containers[].resources'
{
  "limits": {
    "memory": "2Gi"
  },
  "requests": {
    "cpu": "900m",
    "memory": "1Gi"
  }
}

Let’s check the ClickHouse resources,

➤ kubectl get clickhouse -n demo clickhouse-prod -o json | jq '.spec.clusterTopology.cluster.podTemplate.spec.containers[0].resources'
{
  "limits": {
    "memory": "2Gi"
  },
  "requests": {
    "cpu": "900m",
    "memory": "1Gi"
  }
}

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

We are now ready to apply the ClickHouseAutoscaler 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 ClickHouseAutoscaler Object.

Create ClickHouseAutoscaler Object

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

apiVersion: autoscaling.kubedb.com/v1alpha1
kind: ClickHouseAutoscaler
metadata:
  name: ch-compute-autoscale
  namespace: demo
spec:
  databaseRef:
    name: clickhouse-prod
  compute:
    clickhouse:
      trigger: "On"
      podLifeTimeThreshold: 5m
      resourceDiffPercentage: 20
      minAllowed:
        cpu: 1
        memory: 2Gi
      maxAllowed:
        cpu: 2
        memory: 3Gi
      controlledResources: ["cpu", "memory"]
      containerControlledValues: "RequestsAndLimits"

Here,

spec.databaseRef.name specifies that we are performing compute resource autoscaling on clickhouse-autoscale.
spec.compute.clickhouse.trigger specifies that compute resource autoscaling is enabled for this clickhouse.
spec.compute.clickhouse.podLifeTimeThreshold specifies the minimum lifetime for at least one of the pod to initiate a vertical scaling.
spec.compute.clickhouse.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.clickhouse.minAllowed specifies the minimum allowed resources for this clickhouse.
spec.compute.clickhouse.maxAllowed specifies the maximum allowed resources for this clickhouse.
spec.compute.clickhouse.controlledResources specifies the resources that are controlled by the autoscaler.
spec.compute.clickhouse.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 ClickHouseAutoscaler CR we have shown above,

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2025.10.17/docs/examples/clickhouse/autoscaling/compute/clickhouse-autoscaler-ops.yaml
clickhouseautoscaler.autoscaling.kubedb.com/ch-compute-autoscale created

Verify Autoscaling is set up successfully

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

➤ kubectl get clickhouseautoscaler -n demo
NAME                   AGE
ch-compute-autoscale   4m3s

➤ kubectl describe clickhouseautoscaler -n demo ch-compute-autoscale
Name:         ch-compute-autoscale
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  autoscaling.kubedb.com/v1alpha1
Kind:         ClickHouseAutoscaler
Metadata:
  Creation Timestamp:  2025-10-07T05:36:00Z
  Generation:          1
  Owner References:
    API Version:           kubedb.com/v1alpha2
    Block Owner Deletion:  true
    Controller:            true
    Kind:                  ClickHouse
    Name:                  clickhouse-prod
    UID:                   35393926-cb6b-46c2-814c-1ca563783128
  Resource Version:        698948
  UID:                     e8a75e40-c03c-401b-9b1d-647479c4fe67
Spec:
  Compute:
    Clickhouse:
      Container Controlled Values:  RequestsAndLimits
      Controlled Resources:
        cpu
        memory
      Max Allowed:
        Cpu:     2
        Memory:  3Gi
      Min Allowed:
        Cpu:                     1
        Memory:                  2Gi
      Pod Life Time Threshold:   5m0s
      Resource Diff Percentage:  20
      Trigger:                   On
  Database Ref:
    Name:  clickhouse-prod
  Ops Request Options:
    Apply:  IfReady
Status:
  Checkpoints:
    Cpu Histogram:
      Bucket Weights:
        Index:              2
        Weight:             2070
        Index:              5
        Weight:             10000
        Index:              6
        Weight:             1344
      Reference Timestamp:  2025-10-07T05:40:00Z
      Total Weight:         0.5562658287128397
    First Sample Start:     2025-10-07T05:35:47Z
    Last Sample Start:      2025-10-07T05:38:54Z
    Last Update Time:       2025-10-07T05:39:06Z
    Memory Histogram:
      Reference Timestamp:  2025-10-07T05:40:00Z
    Ref:
      Container Name:     clickhouse
      Vpa Object Name:    clickhouse-prod-appscode-cluster-shard-1
    Total Samples Count:  8
    Version:              v3
    Cpu Histogram:
      Bucket Weights:
        Index:              5
        Weight:             10000
        Index:              6
        Weight:             5380
      Reference Timestamp:  2025-10-07T05:40:00Z
      Total Weight:         0.6734523183104338
    First Sample Start:     2025-10-07T05:35:42Z
    Last Sample Start:      2025-10-07T05:39:45Z
    Last Update Time:       2025-10-07T05:40:06Z
    Memory Histogram:
      Bucket Weights:
        Index:              15
        Weight:             9840
        Index:              16
        Weight:             10000
        Index:              17
        Weight:             9840
        Index:              19
        Weight:             10000
      Reference Timestamp:  2025-10-07T05:40:00Z
      Total Weight:         3.868337950095009
    Ref:
      Container Name:     clickhouse
      Vpa Object Name:    clickhouse-prod-appscode-cluster-shard-0
    Total Samples Count:  9
    Version:              v3
  Conditions:
    Last Transition Time:  2025-10-07T05:37:06Z
    Message:               Successfully created ClickHouseOpsRequest demo/chops-clickhouse-prod-appscode-cluster-shard-0-ckc28v
    Observed Generation:   1
    Reason:                CreateOpsRequest
    Status:                True
    Type:                  CreateOpsRequest
  Vpas:
    Conditions:
      Last Transition Time:  2025-10-07T05:38:06Z
      Status:                True
      Type:                  RecommendationProvided
    Recommendation:
      Container Recommendations:
        Container Name:  clickhouse
        Lower Bound:
          Cpu:     1
          Memory:  2Gi
        Target:
          Cpu:     1
          Memory:  2Gi
        Uncapped Target:
          Cpu:     100m
          Memory:  351198544
        Upper Bound:
          Cpu:     2
          Memory:  3Gi
    Vpa Name:      clickhouse-prod-appscode-cluster-shard-1
    Conditions:
      Last Transition Time:  2025-10-07T05:36:06Z
      Status:                True
      Type:                  RecommendationProvided
    Recommendation:
      Container Recommendations:
        Container Name:  clickhouse
        Lower Bound:
          Cpu:     1
          Memory:  2Gi
        Target:
          Cpu:     1
          Memory:  2Gi
        Uncapped Target:
          Cpu:     100m
          Memory:  380258472
        Upper Bound:
          Cpu:     2
          Memory:  3Gi
    Vpa Name:      clickhouse-prod-appscode-cluster-shard-0
Events:            <none>

So, the ClickHouseautoscaler resource is created successfully.

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

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

$ watch kubectl get clickhouseopsrequest -n demo
Every 2.0s: kubectl get clickhouseopsrequest -n demo
NAME                                        TYPE              STATUS        AGE
chops-clickhouse-prod-appscode-cluster-shard-0-ckc28v   VerticalScaling   Progressing   1m28s

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

$ watch kubectl get clickhouseopsrequest -n demo
Every 2.0s: kubectl get clickhouseopsrequest -n demo
NAME                                        TYPE              STATUS       AGE
chops-clickhouse-prod-appscode-cluster-shard-0-ckc28v   VerticalScaling   Successful   3m34s

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

➤ kubectl describe clickhouseopsrequest -n demo chops-clickhouse-prod-appscode-cluster-shard-0-ckc28v 
Name:         chops-clickhouse-prod-appscode-cluster-shard-0-ckc28v
Namespace:    demo
Labels:       app.kubernetes.io/component=database
              app.kubernetes.io/instance=clickhouse-prod
              app.kubernetes.io/managed-by=kubedb.com
              app.kubernetes.io/name=clickhouses.kubedb.com
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         ClickHouseOpsRequest
Metadata:
  Creation Timestamp:  2025-10-07T05:37:06Z
  Generation:          1
  Owner References:
    API Version:           autoscaling.kubedb.com/v1alpha1
    Block Owner Deletion:  true
    Controller:            true
    Kind:                  ClickHouseAutoscaler
    Name:                  ch-compute-autoscale
    UID:                   e8a75e40-c03c-401b-9b1d-647479c4fe67
  Resource Version:        698821
  UID:                     171e1151-821b-4c51-b028-a18ff75a2133
Spec:
  Apply:  IfReady
  Database Ref:
    Name:  clickhouse-prod
  Type:    VerticalScaling
  Vertical Scaling:
    Node:
      Resources:
        Limits:
          Memory:  4Gi
        Requests:
          Cpu:     1
          Memory:  2Gi
Status:
  Conditions:
    Last Transition Time:  2025-10-07T05:37:06Z
    Message:               ClickHouse ops-request has started to vertically scaling the ClickHouse nodes
    Observed Generation:   1
    Reason:                VerticalScaling
    Status:                True
    Type:                  VerticalScaling
    Last Transition Time:  2025-10-07T05:37:09Z
    Message:               Successfully updated PetSets Resources
    Observed Generation:   1
    Reason:                UpdatePetSets
    Status:                True
    Type:                  UpdatePetSets
    Last Transition Time:  2025-10-07T05:39:04Z
    Message:               Successfully Restarted Pods With Resources
    Observed Generation:   1
    Reason:                RestartPods
    Status:                True
    Type:                  RestartPods
    Last Transition Time:  2025-10-07T05:37:15Z
    Message:               get pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-0-0
    Observed Generation:   1
    Status:                True
    Type:                  GetPod--clickhouse-prod-appscode-cluster-shard-0-0
    Last Transition Time:  2025-10-07T05:37:15Z
    Message:               evict pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-0-0
    Observed Generation:   1
    Status:                True
    Type:                  EvictPod--clickhouse-prod-appscode-cluster-shard-0-0
    Last Transition Time:  2025-10-07T05:37:19Z
    Message:               running pod; ConditionStatus:False
    Observed Generation:   1
    Status:                False
    Type:                  RunningPod
    Last Transition Time:  2025-10-07T05:37:44Z
    Message:               get pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-0-1
    Observed Generation:   1
    Status:                True
    Type:                  GetPod--clickhouse-prod-appscode-cluster-shard-0-1
    Last Transition Time:  2025-10-07T05:37:44Z
    Message:               evict pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-0-1
    Observed Generation:   1
    Status:                True
    Type:                  EvictPod--clickhouse-prod-appscode-cluster-shard-0-1
    Last Transition Time:  2025-10-07T05:38:04Z
    Message:               get pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-1-0
    Observed Generation:   1
    Status:                True
    Type:                  GetPod--clickhouse-prod-appscode-cluster-shard-1-0
    Last Transition Time:  2025-10-07T05:38:04Z
    Message:               evict pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-1-0
    Observed Generation:   1
    Status:                True
    Type:                  EvictPod--clickhouse-prod-appscode-cluster-shard-1-0
    Last Transition Time:  2025-10-07T05:38:24Z
    Message:               get pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-1-1
    Observed Generation:   1
    Status:                True
    Type:                  GetPod--clickhouse-prod-appscode-cluster-shard-1-1
    Last Transition Time:  2025-10-07T05:38:24Z
    Message:               evict pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-1-1
    Observed Generation:   1
    Status:                True
    Type:                  EvictPod--clickhouse-prod-appscode-cluster-shard-1-1
    Last Transition Time:  2025-10-07T05:39:04Z
    Message:               Successfully completed the vertical scaling for ClickHouse
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type     Reason                                                                               Age    From                         Message
  ----     ------                                                                               ----   ----                         -------
  Normal   Starting                                                                             7m42s  KubeDB Ops-manager Operator  Start processing for ClickHouseOpsRequest: demo/chops-clickhouse-prod-appscode-cluster-shard-0-ckc28v
  Normal   Starting                                                                             7m42s  KubeDB Ops-manager Operator  Pausing ClickHouse databse: demo/clickhouse-prod
  Normal   Successful                                                                           7m42s  KubeDB Ops-manager Operator  Successfully paused ClickHouse database: demo/clickhouse-prod for ClickHouseOpsRequest: chops-clickhouse-prod-appscode-cluster-shard-0-ckc28v
  Normal   UpdatePetSets                                                                        7m39s  KubeDB Ops-manager Operator  Successfully updated PetSets Resources
  Warning  get pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-0-0    7m33s  KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-0-0
  Warning  evict pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-0-0  7m33s  KubeDB Ops-manager Operator  evict pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-0-0
  Warning  running pod; ConditionStatus:False                                                   7m29s  KubeDB Ops-manager Operator  running pod; ConditionStatus:False
  Warning  get pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-0-1    7m4s   KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-0-1
  Warning  evict pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-0-1  7m4s   KubeDB Ops-manager Operator  evict pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-0-1
  Warning  get pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-1-0    6m44s  KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-1-0
  Warning  evict pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-1-0  6m44s  KubeDB Ops-manager Operator  evict pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-1-0
  Warning  get pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-1-1    6m24s  KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-1-1
  Warning  evict pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-1-1  6m24s  KubeDB Ops-manager Operator  evict pod; ConditionStatus:True; PodName:clickhouse-prod-appscode-cluster-shard-1-1
  Normal   RestartPods                                                                          5m44s  KubeDB Ops-manager Operator  Successfully Restarted Pods With Resources
  Normal   Starting                                                                             5m44s  KubeDB Ops-manager Operator  Resuming ClickHouse database: demo/clickhouse-prod
  Normal   Successful                                                                           5m44s  KubeDB Ops-manager Operator  Successfully resumed ClickHouse database: demo/clickhouse-prod for ClickHouseOpsRequest: chops-clickhouse-prod-appscode-cluster-shard-0-ckc28v

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

➤ kubectl get pod -n demo clickhouse-prod-appscode-cluster-shard-0-0 -o json | jq '.spec.containers[].resources'
{
  "limits": {
    "memory": "4Gi"
  },
  "requests": {
    "cpu": "1",
    "memory": "2Gi"
  }
}


➤ kubectl get clickhouse -n demo clickhouse-prod -o json | jq '.spec.clusterTopology.cluster.podTemplate.spec.containers[0].resources'
{
  "limits": {
    "memory": "4Gi"
  },
  "requests": {
    "cpu": "1",
    "memory": "2Gi"
  }
}

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

Cleaning Up

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

kubectl delete ch -n demo clickhouse-prod
kubectl delete clickhouseautoscaler -n demo ch-compute-autoscale

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