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You are looking at the documentation of a prior release. To read the documentation of the latest release, please visit here.

New to KubeDB? Please start here.

Horizontal Scale ZooKeeper

This guide will show you how to use KubeDB Ops-manager operator to scale the ZooKeeper 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/zookeeper directory of kubedb/docs repository.

Apply Horizontal Scaling on zookeeper

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

Deploy ZooKeeper

In this section, we are going to deploy a ZooKeeper. We are going to deploy a ZooKeeper with version 3.8.3. Then, in the next section we will scale the zookeeper using ZooKeeperOpsRequest CRD. Below is the YAML of the ZooKeeper CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: ZooKeeper
metadata:
  name: zk-quickstart
  namespace: demo
spec:
  version: "3.8.3"
  adminServerPort: 8080
  replicas: 3
  storage:
    resources:
      requests:
        storage: "1Gi"
    storageClassName: "standard"
    accessModes:
      - ReadWriteOnce
  deletionPolicy: "WipeOut"

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

$ kubectl create -f https://github.com/kubedb/docs/raw/v2025.5.30/docs/examples/zookeeper/scaling/zookeeper.yaml
zookeeper.kubedb.com/zk-quickstart created

Now, wait until zk-quickstart has status Ready. i.e,

$ kubectl get zk -n demo
NAME            VERSION    STATUS    AGE
zk-quickstart   3.8.3      Ready     5m56s

Let’s check the number of replicas this zookeeper has from the ZooKeeper object, number of pods the PetSet have,

$ kubectl get zookeeper -n demo zk-quickstart -o json | jq '.spec.replicas'
3

$ kubectl get petset -n demo zk-quickstart -o json | jq '.spec.replicas'
3

We can see from both command that the zookeeper has 3 replicas.

We are now ready to apply the ZooKeeperOpsRequest CR to scale this zookeeper.

Scale Up Replicas

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

Create ZooKeeperOpsRequest

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

apiVersion: ops.kubedb.com/v1alpha1
kind: ZooKeeperOpsRequest
metadata:
  name: zookeeper-horizontal-scale-up
  namespace: demo
spec:
  type: HorizontalScaling
  databaseRef:
    name: zk-quickstart
  horizontalScaling:
    replicas: 5

Here,

  • spec.databaseRef.name specifies that we are performing horizontal scaling operation on zk-quickstart zookeeper.
  • spec.type specifies that we are performing HorizontalScaling on our zookeeper.
  • spec.horizontalScaling.replicas specifies the desired replicas after scaling.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2025.5.30/docs/examples/zookeeper/scaling/horizontal-scaling/zk-hscale-up-ops.yaml
zookeeperopsrequest.ops.kubedb.com/zookeeper-horizontal-scale-up created

Verify replicas scaled up successfully

If everything goes well, KubeDB Ops-manager operator will update the replicas of ZooKeeper object and related PetSet.

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

$ watch kubectl get zookeeperopsrequest -n demo
NAME                            TYPE                STATUS       AGE
zookeeper-horizontal-scale-up   HorizontalScaling   Successful   2m49s

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

$ kubectl describe zookeeperopsrequest -n demo zookeeper-horizontal-scale-up
Name:         zookeeper-horizontal-scale-up
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         ZooKeeperOpsRequest
Metadata:
  Creation Timestamp:  2024-10-25T13:37:43Z
  Generation:          1
  Resource Version:    1198117
  UID:                 bfa6fb3f-5eb2-456c-8a3e-7a59097add0a
Spec:
  Apply:  IfReady
  Database Ref:
    Name:  zk-quickstart
  Horizontal Scaling:
    Replicas:  5
  Type:        HorizontalScaling
Status:
  Conditions:
    Last Transition Time:  2024-10-25T13:37:43Z
    Message:               ZooKeeper ops-request has started to horizontally scaling the nodes
    Observed Generation:   1
    Reason:                HorizontalScaling
    Status:                True
    Type:                  HorizontalScaling
    Last Transition Time:  2024-10-25T13:38:03Z
    Message:               Successfully Scaled Up Node
    Observed Generation:   1
    Reason:                HorizontalScaleUp
    Status:                True
    Type:                  HorizontalScaleUp
    Last Transition Time:  2024-10-25T13:37:48Z
    Message:               patch petset; ConditionStatus:True; PodName:zk-quickstart-4
    Observed Generation:   1
    Status:                True
    Type:                  PatchPetset--zk-quickstart-4
    Last Transition Time:  2024-10-25T13:37:48Z
    Message:               zk-quickstart already has desired replicas
    Observed Generation:   1
    Reason:                HorizontalScale
    Status:                True
    Type:                  HorizontalScale
    Last Transition Time:  2024-10-25T13:37:58Z
    Message:               is pod ready; ConditionStatus:True; PodName:zk-quickstart-4
    Observed Generation:   1
    Status:                True
    Type:                  IsPodReady--zk-quickstart-4
    Last Transition Time:  2024-10-25T13:37:58Z
    Message:               is node healthy; ConditionStatus:True; PodName:zk-quickstart-4
    Observed Generation:   1
    Status:                True
    Type:                  IsNodeHealthy--zk-quickstart-4
    Last Transition Time:  2024-10-25T13:38:03Z
    Message:               Successfully updated ZooKeeper
    Observed Generation:   1
    Reason:                UpdateDatabase
    Status:                True
    Type:                  UpdateDatabase
    Last Transition Time:  2024-10-25T13:38:03Z
    Message:               Successfully completed the HorizontalScaling for FerretDB
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type     Reason                                                          Age   From                         Message
  ----     ------                                                          ----  ----                         -------
  Normal   Starting                                                        47s   KubeDB Ops-manager Operator  Start processing for ZooKeeperOpsRequest: demo/horizontal-scale-up
  Warning  patch petset; ConditionStatus:True; PodName:zk-quickstart-4     42s   KubeDB Ops-manager Operator  patch petset; ConditionStatus:True; PodName:zk-quickstart-4
  Warning  is pod ready; ConditionStatus:False; PodName:zk-quickstart-4    37s   KubeDB Ops-manager Operator  is pod ready; ConditionStatus:False; PodName:zk-quickstart-4
  Warning  is pod ready; ConditionStatus:True; PodName:zk-quickstart-4     32s   KubeDB Ops-manager Operator  is pod ready; ConditionStatus:True; PodName:zk-quickstart-4
  Warning  is node healthy; ConditionStatus:True; PodName:zk-quickstart-4  32s   KubeDB Ops-manager Operator  is node healthy; ConditionStatus:True; PodName:zk-quickstart-4
  Normal   HorizontalScaleUp                                               27s   KubeDB Ops-manager Operator  Successfully Scaled Up Node
  Normal   UpdateDatabase                                                  27s   KubeDB Ops-manager Operator  Successfully updated ZooKeeper
  Normal   Starting                                                        27s   KubeDB Ops-manager Operator  Resuming ZooKeeper database: demo/zk-quickstart
  Normal   Successful                                                      27s   KubeDB Ops-manager Operator  Successfully resumed ZooKeeper database: demo/zk-quickstart for ZooKeeperOpsRequest: horizontal-scale-up

Now, we are going to verify the number of replicas this zookeeper has from the Pgpool object, number of pods the PetSet have,

$ kubectl get zookeeper -n demo zk-quickstart -o json | jq '.spec.replicas'
5

$ kubectl get petset -n demo zk-quickstart -o json | jq '.spec.replicas'
5

From all the above outputs we can see that the replicas of the zookeeper is 5. That means we have successfully scaled up the replicas of the ZooKeeper.

Scale Down Replicas

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

Create ZooKeeperOpsRequest

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

apiVersion: ops.kubedb.com/v1alpha1
kind: ZooKeeperOpsRequest
metadata:
  name: zookeeper-horizontal-scale-down
  namespace: demo
spec:
  type: HorizontalScaling
  databaseRef:
    name: zk-quickstart
  horizontalScaling:
    replicas: 3

Here,

  • spec.databaseRef.name specifies that we are performing horizontal scaling down operation on zookeeper zookeeper.
  • spec.type specifies that we are performing HorizontalScaling on our zookeeper.
  • spec.horizontalScaling.replicas specifies the desired replicas after scaling.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2025.5.30/docs/examples/zookeeper/scaling/horizontal-scaling/zk-hscale-down-ops.yaml
zookeeperopsrequest.ops.kubedb.com/zookeeper-horizontal-scale-down created

Verify replicas scaled down successfully

If everything goes well, KubeDB Ops-manager operator will update the replicas of ZooKeeper object and related PetSet.

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

$ watch kubectl get zookeeperopsrequest -n demo
NAME                              TYPE                STATUS       AGE
zookeeper-horizontal-scale-down   HorizontalScaling   Successful   75s

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

$ kubectl describe zookeeperopsrequest -n demo zookeeper-horizontal-scale-down
Name:         zookeeper-horizontal-scale-down
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         ZooKeeperOpsRequest
Metadata:
  Creation Timestamp:  2024-10-25T13:58:45Z
  Generation:          1
  Resource Version:    1199568
  UID:                 18b2adbb-9fbd-44fe-a265-e7eb4a292798
Spec:
  Apply:  IfReady
  Database Ref:
    Name:  zk-quickstart
  Horizontal Scaling:
    Replicas:  3
  Type:        HorizontalScaling
Status:
  Conditions:
    Last Transition Time:  2024-10-25T13:58:45Z
    Message:               ZooKeeper ops-request has started to horizontally scaling the nodes
    Observed Generation:   1
    Reason:                HorizontalScaling
    Status:                True
    Type:                  HorizontalScaling
    Last Transition Time:  2024-10-25T14:00:23Z
    Message:               Successfully Scaled Down Node
    Observed Generation:   1
    Reason:                HorizontalScaleDown
    Status:                True
    Type:                  HorizontalScaleDown
    Last Transition Time:  2024-10-25T13:58:53Z
    Message:               patch petset; ConditionStatus:True; PodName:zk-quickstart-4
    Observed Generation:   1
    Status:                True
    Type:                  PatchPetset--zk-quickstart-4
    Last Transition Time:  2024-10-25T13:58:58Z
    Message:               get pod; ConditionStatus:False
    Observed Generation:   1
    Status:                False
    Type:                  GetPod
    Last Transition Time:  2024-10-25T13:59:28Z
    Message:               get pod; ConditionStatus:True; PodName:zk-quickstart-4
    Observed Generation:   1
    Status:                True
    Type:                  GetPod--zk-quickstart-4
    Last Transition Time:  2024-10-25T13:59:28Z
    Message:               delete pvc; ConditionStatus:True
    Observed Generation:   1
    Status:                True
    Type:                  DeletePvc
    Last Transition Time:  2024-10-25T13:59:38Z
    Message:               patch petset; ConditionStatus:True; PodName:zk-quickstart-3
    Observed Generation:   1
    Status:                True
    Type:                  PatchPetset--zk-quickstart-3
    Last Transition Time:  2024-10-25T13:59:38Z
    Message:               zk-quickstart already has desired replicas
    Observed Generation:   1
    Reason:                HorizontalScale
    Status:                True
    Type:                  HorizontalScale
    Last Transition Time:  2024-10-25T14:00:13Z
    Message:               get pod; ConditionStatus:True; PodName:zk-quickstart-3
    Observed Generation:   1
    Status:                True
    Type:                  GetPod--zk-quickstart-3
    Last Transition Time:  2024-10-25T14:00:23Z
    Message:               Successfully updated ZooKeeper
    Observed Generation:   1
    Reason:                UpdateDatabase
    Status:                True
    Type:                  UpdateDatabase
    Last Transition Time:  2024-10-25T14:00:23Z
    Message:               Successfully completed the HorizontalScaling for FerretDB
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type     Reason                                                       Age    From                         Message
  ----     ------                                                       ----   ----                         -------
  Normal   Starting                                                     3m27s  KubeDB Ops-manager Operator  Start processing for ZooKeeperOpsRequest: demo/horizontal-scale-down
  Normal   Starting                                                     3m27s  KubeDB Ops-manager Operator  Pausing ZooKeeper database: demo/zk-quickstart
  Normal   Successful                                                   3m27s  KubeDB Ops-manager Operator  Successfully paused ZooKeeper database: demo/zk-quickstart for ZooKeeperOpsRequest: horizontal-scale-down
  Warning  patch petset; ConditionStatus:True; PodName:zk-quickstart-4  3m19s  KubeDB Ops-manager Operator  patch petset; ConditionStatus:True; PodName:zk-quickstart-4
  Warning  get pod; ConditionStatus:False                               3m14s  KubeDB Ops-manager Operator  get pod; ConditionStatus:False
  Warning  get pod; ConditionStatus:True; PodName:zk-quickstart-4       2m44s  KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:zk-quickstart-4
  Warning  delete pvc; ConditionStatus:True                             2m44s  KubeDB Ops-manager Operator  delete pvc; ConditionStatus:True
  Warning  get pod; ConditionStatus:False                               2m44s  KubeDB Ops-manager Operator  get pod; ConditionStatus:False
  Warning  get pod; ConditionStatus:True; PodName:zk-quickstart-4       2m39s  KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:zk-quickstart-4
  Warning  delete pvc; ConditionStatus:True                             2m39s  KubeDB Ops-manager Operator  delete pvc; ConditionStatus:True
  Warning  get pod; ConditionStatus:True; PodName:zk-quickstart-4       2m39s  KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:zk-quickstart-4
  Warning  patch petset; ConditionStatus:True; PodName:zk-quickstart-3  2m34s  KubeDB Ops-manager Operator  patch petset; ConditionStatus:True; PodName:zk-quickstart-3
  Warning  get pod; ConditionStatus:False                               2m29s  KubeDB Ops-manager Operator  get pod; ConditionStatus:False
  Warning  get pod; ConditionStatus:True; PodName:zk-quickstart-3       119s   KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:zk-quickstart-3
  Warning  delete pvc; ConditionStatus:True                             119s   KubeDB Ops-manager Operator  delete pvc; ConditionStatus:True
  Warning  get pod; ConditionStatus:False                               119s   KubeDB Ops-manager Operator  get pod; ConditionStatus:False
  Warning  get pod; ConditionStatus:True; PodName:zk-quickstart-3       114s   KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:zk-quickstart-3
  Warning  delete pvc; ConditionStatus:True                             114s   KubeDB Ops-manager Operator  delete pvc; ConditionStatus:True
  Warning  get pod; ConditionStatus:True; PodName:zk-quickstart-3       114s   KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:zk-quickstart-3
  Normal   HorizontalScaleDown                                          109s   KubeDB Ops-manager Operator  Successfully Scaled Down Node
  Normal   UpdateDatabase                                               109s   KubeDB Ops-manager Operator  Successfully updated ZooKeeper
  Normal   Starting                                                     109s   KubeDB Ops-manager Operator  Resuming ZooKeeper database: demo/zk-quickstart
  Normal   Successful                                                   109s   KubeDB Ops-manager Operator  Successfully resumed ZooKeeper database: demo/zk-quickstart for ZooKeeperOpsRequest: horizontal-scale-down

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

$ kubectl get zookeeper -n demo zk-quickstart -o json | jq '.spec.replicas'
3

$ kubectl get petset -n demo zk-quickstart -o json | jq '.spec.replicas'
3

From all the above outputs we can see that the replicas of the zookeeper is 3. That means we have successfully scaled up the replicas of the ZooKeeper.

Cleaning Up

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

kubectl delete zk -n demo
kubectl delete zookeeperopsrequest -n demo zookeeper-horizontal-scale-down

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