Version: Preview

Scale a Kafka cluster

You can scale a Kafka cluster in two ways, vertical scaling and horizontal scaling.

Vertical scaling

You can vertically scale a cluster by changing resource requirements and limits (CPU and storage). For example, you can change the resource class from 1C2G to 2C4G by performing vertical scaling.

Before you start

Check whether the cluster status is Running. Otherwise, the following operations may fail.

kbcli
kubectl

kbcli cluster list mycluster -n demo
>
NAME        NAMESPACE   CLUSTER-DEFINITION   VERSION       TERMINATION-POLICY   STATUS    CREATED-TIME
mycluster   demo        kafka                kafka-3.3.2   Delete               Running   Sep 27,2024 15:15 UTC+0800

kubectl -n demo get cluster mycluster
>
NAME           CLUSTER-DEFINITION   VERSION        TERMINATION-POLICY   STATUS     AGE
mycluster      kafka                kafka-3.3.2    Delete               Running    19m

Steps

kbcli
OpsRequest
Edit cluster YAML file

Configure the parameters --components, --memory, and --cpu and run the command.
```
 kbcli cluster vscale mycluster -n demo --components="broker" --memory="4Gi" --cpu="2" 
```
- --components value can be broker or controller.
  - broker: all nodes in the combined mode, or all the broker node in the separated node.
  - controller: all the corresponding nodes in the separated mode.
- --memory describes the requested and limited size of the component memory.
- --cpu describes the requested and limited size of the component CPU.
Validate the vertical scaling operation.
- View the OpsRequest progress.
  KubeBlocks outputs a command automatically for you to view the OpsRequest progress. The output includes the status of this OpsRequest and Pods. When the status is Succeed, this OpsRequest is completed.
```
kbcli cluster describe-ops mycluster-verticalscaling-g67k9 -n demo
```
- Check the cluster status.
```
kbcli cluster list mycluster -n demo
>
NAME             NAMESPACE        CLUSTER-DEFINITION       VERSION                TERMINATION-POLICY        STATUS          CREATED-TIME
mycluster        demo         kafka                    kafka-3.3.2            Delete                    Updating        Sep 27,2024 15:15 UTC+0800
```
- STATUS=Updating: it means the vertical scaling is in progress.
- STATUS=Running: it means the vertical scaling operation has been applied.
- STATUS=Abnormal: it means the vertical scaling is abnormal. The reason may be that the number of the normal instances is less than that of the total instance or the leader instance is running properly while others are abnormal.
  To solve the problem, you can manually check whether this error is caused by insufficient resources. Then if AutoScaling is supported by the Kubernetes cluster, the system recovers when there are enough resources. Otherwise, you can create enough resources and troubleshoot with kubectl describe command.

note

Vertical scaling does not synchronize parameters related to CPU and memory and it is required to manually call the OpsRequest of configuration to change parameters accordingly. Refer to Configuration for instructions.

After the OpsRequest status is Succeed or the cluster status is Running again, check whether the corresponding resources change.
```
kbcli cluster describe mycluster -n demo
```

Apply an OpsRequest to the specified cluster. Configure the parameters according to your needs.

kubectl apply -f - <<EOF
apiVersion: apps.kubeblocks.io/v1alpha1
kind: OpsRequest
metadata:
  name: ops-vertical-scaling
  namespace: demo
spec:
  clusterRef: mycluster
  type: VerticalScaling 
  verticalScaling:
  - componentName: broker
    requests:
      memory: "2Gi"
      cpu: "1"
    limits:
      memory: "4Gi"
      cpu: "2"
EOF

Check the operation status to validate the vertical scaling.

kubectl get ops -n demo
>
NAMESPACE   NAME                   TYPE              CLUSTER     STATUS    PROGRESS   AGE
demo        ops-vertical-scaling   VerticalScaling   mycluster   Succeed   3/3        6m

If an error occurs, you can troubleshoot with kubectl describe ops -n demo command to view the events of this operation.

Check whether the corresponding resources change.

kubectl describe cluster mycluster -n demo
>
......
Component Specs:
 Component Def Ref:  kafka
 Enabled Logs:
   running
 DisableExporter:   true
 Name:      kafka
 Replicas:  2
 Resources:
   Limits:
     Cpu:     2
     Memory:  4Gi
   Requests:
     Cpu:     1
     Memory:  2Gi

Change the configuration of spec.componentSpecs.resources in the YAML file. spec.componentSpecs.resources controls the requirement and limit of resources and changing them triggers a vertical scaling.

apiVersion: apps.kubeblocks.io/v1alpha1
kind: Cluster
metadata:
  name: mycluster
  namespace: demo
spec:
  clusterDefinitionRef: kafka
  clusterVersionRef: kafka-3.3.2
  componentSpecs:
  - name: broker
    componentDefRef: broker
    replicas: 1
    resources: # Change the values of resources.
      requests:
        memory: "2Gi"
        cpu: "1"
      limits:
        memory: "4Gi"
        cpu: "2"
    volumeClaimTemplates:
    - name: data
      spec:
        accessModes:
          - ReadWriteOnce
        resources:
          requests:
            storage: 1Gi
  terminationPolicy: Delete

Check whether the corresponding resources change.

kubectl describe cluster mycluster -n demo
>
......
Component Specs:
 Component Def Ref:  kafka
 Enabled Logs:
   running
 DisableExporter:   true
 Name:      kafka
 Replicas:  2
 Resources:
   Limits:
     Cpu:     2
     Memory:  4Gi
   Requests:
     Cpu:     1
     Memory:  2Gi

Horizontal scaling

Horizontal scaling changes the amount of pods. For example, you can scale out replicas from three to five.

From v0.9.0, besides replicas, KubeBlocks also supports scaling in and out instances, refer to the Horizontal Scale tutorial for more details and examples.

Before you start

Check whether the cluster STATUS is Running. Otherwise, the following operations may fail.

kbcli
kubectl

kbcli cluster list mycluster -n demo
>
NAME        NAMESPACE   CLUSTER-DEFINITION   VERSION       TERMINATION-POLICY   STATUS    CREATED-TIME
mycluster   demo        kafka                kafka-3.3.2   Delete               Running   Sep 27,2024 15:15 UTC+0800

kubectl -n demo get cluster mycluster
>
NAME           CLUSTER-DEFINITION   VERSION        TERMINATION-POLICY   STATUS     AGE
mycluster      kafka                kafka-3.3.2    Delete               Running    19m

You are not recommended to perform horizontal scaling on the controller node, including the controller node both in combined mode and separated node.
When scaling in horizontally, you must know the topic partition storage. If the topic has only one replication, data loss may caused when you scale in broker.

Steps

kbcli
OpsRequest
Edit cluster YAML file

Configure the parameters --components and --replicas, and run the command.
```
kbcli cluster hscale mycluster -n demo --components="broker" --replicas=3
```
- --components describes the component name ready for horizontal scaling.
- --replicas describes the replica amount of the specified components. Edit the amount based on your demands to scale in or out replicas.
Validate the horizontal scaling operation.
- View the OpsRequest progress.
  KubeBlocks outputs a command automatically for you to view the OpsRequest progress. The output includes the status of this OpsRequest and Pods. When the status is Succeed, this OpsRequest is completed.
```
kbcli cluster describe-ops mycluster-horizontalscaling-ffp9p -n demo
```
- View the cluster satus.
```
kbcli cluster list mycluster -n demo
```
  - STATUS=Updating: it means horizontal scaling is in progress.
  - STATUS=Running: it means horizontal scaling has been applied.
Check whether the corresponding resources change.
```
kbcli cluster describe mycluster -n demo
```

Apply an OpsRequest to a specified cluster. Configure the parameters according to your needs.

The example below means adding two replicas.

kubectl apply -f - <<EOF
apiVersion: apps.kubeblocks.io/v1alpha1
kind: OpsRequest
metadata:
  name: ops-horizontal-scaling
  namespace: demo
spec:
  clusterRef: mycluster
  type: HorizontalScaling
  horizontalScaling:
  - componentName: broker
    scaleOut:
      replicaChanges: 2
EOF

If you want to scale in replicas, replace scaleOut with scaleIn.

The example below means deleting two replicas.

kubectl apply -f - <<EOF
apiVersion: apps.kubeblocks.io/v1alpha1
kind: OpsRequest
metadata:
  name: ops-horizontal-scaling
  namespace: demo
spec:
  clusterRef: mycluster
  type: HorizontalScaling
  horizontalScaling:
  - componentName: broker
    scaleIn:
      replicaChanges: 2
EOF

Check the operation status to validate the horizontal scaling.

kubectl get ops -n demo
>
NAMESPACE   NAME                     TYPE                CLUSTER     STATUS    PROGRESS   AGE
demo        ops-horizontal-scaling   HorizontalScaling   mycluster   Succeed   3/3        6m

If an error occurs, you can troubleshoot with kubectl describe ops -n demo command to view the events of this operation.

Check whether the corresponding resources change.

kubectl describe cluster mycluster -n demo
>
......
Component Specs:
 Component Def Ref:  kafka
 Enabled Logs:
   running
 DisableExporter:   true
 Name:      kafka
 Replicas:  2
 Resources:
   Limits:
     Cpu:     2
     Memory:  4Gi
   Requests:
     Cpu:     1
     Memory:  2Gi

Change the configuration of spec.componentSpecs.replicas in the YAML file. spec.componentSpecs.replicas stands for the pod amount and changing this value triggers a horizontal scaling of a cluster.

kubectl edit cluster mycluster -n demo
>
apiVersion: apps.kubeblocks.io/v1alpha1
kind: Cluster
metadata:
  name: mycluster
  namespace: demo
spec:
  clusterDefinitionRef: kafka
  clusterVersionRef: kafka-3.3.2 
  componentSpecs:
  - name: broker
    componentDefRef: broker
    replicas: 2 # Change the amount
    volumeClaimTemplates:
    - name: data
      spec:
        accessModes:
          - ReadWriteOnce
        resources:
          requests:
            storage: 20Gi
 terminationPolicy: Delete

Check whether the corresponding resources change.

kubectl describe cluster mycluster -n demo
>
......
Component Specs:
 Component Def Ref:  kafka
 Enabled Logs:
   running
 DisableExporter:   true
 Name:      kafka
 Replicas:  2
 Resources:
   Limits:
     Cpu:     2
     Memory:  4Gi
   Requests:
     Cpu:     1
     Memory:  2Gi

Handle the snapshot exception

If STATUS=ConditionsError occurs during the horizontal scaling process, you can find the cause from cluster.status.condition.message for troubleshooting.

In the example below, a snapshot exception occurs.

Status:
  conditions: 
  - lastTransitionTime: "2023-02-08T04:20:26Z"
    message: VolumeSnapshot/mycluster-kafka-scaling-dbqgp: Failed to set default snapshot
      class with error cannot find default snapshot class
    reason: ApplyResourcesFailed
    status: "False"
    type: ApplyResources

Reason

This exception occurs because the VolumeSnapshotClass is not configured. This exception can be fixed after configuring VolumeSnapshotClass, but the horizontal scaling cannot continue to run. It is because the wrong backup (volumesnapshot is generated by backup) and volumesnapshot generated before still exist. Delete these two wrong resources and then KubeBlocks re-generates new resources.

Steps:

Configure the VolumeSnapshotClass by running the command below.

kubectl create -f - <<EOF
apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
  name: csi-aws-vsc
  annotations:
    snapshot.storage.kubernetes.io/is-default-class: "true"
driver: ebs.csi.aws.com
deletionPolicy: Delete
EOF

Delete the wrong backup (volumesnapshot is generated by backup) and volumesnapshot resources.

kubectl delete backup -l app.kubernetes.io/instance=mycluster -n demo

kubectl delete volumesnapshot -l app.kubernetes.io/instance=mycluster -n demo

Result

The horizontal scaling continues after backup and volumesnapshot are deleted and the cluster restores to running status.

Scale a Kafka cluster

Vertical scaling​

Before you start​

Steps​

Horizontal scaling​

Before you start​

Steps​

Handle the snapshot exception​

Vertical scaling

Before you start

Steps

Horizontal scaling

Before you start

Steps

Handle the snapshot exception