Skip to main content
Version: Preview

Scale for 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, if you need to change the resource class from 1C2G to 2C4G, vertical scaling is what you need.

Before you start​

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

kbcli cluster list
>
NAME            NAMESPACE   CLUSTER-DEFINITION   VERSION       TERMINATION-POLICY   STATUS    CREATED-TIME                 
kafka-cluster   default     kafka                kafka-3.3.2   Delete               Running   Jul 19,2023 18:01 UTC+0800

Steps​

  1. Change configuration.

    Configure the parameters --components, --memory, and --cpu and run the command.

     kbcli cluster vscale kafka-cluster --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.

  2. Check the cluster status to validate the vertical scaling.

    kbcli cluster list kafka-cluster
    >
    NAME                 NAMESPACE        CLUSTER-DEFINITION       VERSION                TERMINATION-POLICY        STATUS          CREATED-TIME
    kafka-cluster        default          kafka                    kafka-3.3.2            Delete                    Updating        Jan 29,2023 14:29 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.

  3. Check whether the corresponding resources change.

    kbcli cluster describe kafka-cluster

Horizontal scaling​

Horizontal scaling changes the amount of pods. For example, you can apply horizontal scaling to scale pods up from three to five. The scaling process includes the backup and restoration of data.

Before you start​

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

  • 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.

    kbcli cluster list
    >
    NAME            NAMESPACE   CLUSTER-DEFINITION   VERSION       TERMINATION-POLICY   STATUS    CREATED-TIME                 
    kafka-cluster   default     kafka                kafka-3.3.2   Delete               Running   Jul 19,2023 18:01 UTC+0800

Steps​

  1. Change configuration.

    Configure the parameters --components and --replicas, and run the command.

    kbcli cluster hscale kafka-cluster \
    --components="broker" --replicas=3
    • --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.

  2. Validate the horizontal scaling operation.

    Check the cluster STATUS to identify the horizontal scaling status.

    kbcli cluster list kafka-cluster
    • STATUS=Updating: it means horizontal scaling is in progress.
    • STATUS=Running: it means horizontal scaling has been applied.

  3. Check whether the corresponding resources change.

    kbcli cluster describe kafka-cluster

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/kafka-cluster-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:

  1. 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

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

    kubectl delete backup -l app.kubernetes.io/instance=kafka-cluster

    kubectl delete volumesnapshot -l app.kubernetes.io/instance=kafka-cluster

Result

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