Scale for a PostgreSQL cluster

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

note

After vertical scaling or horizontal scaling is performed, KubeBlocks automatically matches the appropriate configuration template based on the new specification. This is the KubeBlocks dynamic configuration feature. This feature simplifies the process of configuring parameters, saves time and effort and reduces performance issues caused by incorrect configuration. For detailed instructions, refer to Configuration.

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 cluster list pg-cluster
>
NAME         NAMESPACE   CLUSTER-DEFINITION      VERSION             TERMINATION-POLICY   STATUS    CREATED-TIME
pg-cluster   default     postgresql              postgresql-14.8.0   Delete               Running   Mar 03,2023 18:00 UTC+0800

Steps

1. Change configuration.

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

   kbcli cluster vscale pg-cluster \
   --components="postgresql" \
   --memory="1Gi" --cpu="1" \
   • --components describes the component name ready for vertical scaling.
   • --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 vertical scaling.

   Run the command below to check the cluster status to identify the vertical scaling status.

   kbcli cluster list pg-cluster
   >
   NAME              NAMESPACE        CLUSTER-DEFINITION            VERSION                TERMINATION-POLICY   STATUS    CREATED-TIME
   pg-cluster        default          postgresql-cluster            postgresql-14.8.0      Delete               Running   Mar 03,2023 18:00 UTC+0800
   • STATUS=Updating: it means the vertical scaling is in progress.
   • STATUS=Running: it means the vertical scaling has been applied.
   • STATUS=Abnormal: it means the vertical scaling is abnormal. The reason may be the normal instances number is less than the total instance number or the primary instance is running properly while others are abnormal.

     To solve the problem, you can check manually to see whether resources are sufficient. If AutoScaling is supported, the system recovers when there are enough resources, otherwise, you can create enough resources and check the result with kubectl describe command.

3. Check whether the corresponding resources change.

   kbcli cluster describe pg-cluster

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 Horizontal Scale in API docs for more details and examples.

Before you start

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

kbcli cluster list pg-cluster
>
NAME              NAMESPACE        CLUSTER-DEFINITION        VERSION                TERMINATION-POLICY        STATUS         CREATED-TIME
pg-cluster        default          postgreql                 postgresql-14.8.0      Delete                    Running        Mar 03,2023 19:29 UTC+0800

Steps

1. Change configuration.

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

   kbcli cluster hscale pg-cluster \
   --components="postgresql" --replicas=2
   • --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.

2. Validate the horizontal scaling operation.

   Check the cluster STATUS to identify the horizontal scaling status.

   kbcli cluster list pg-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 pg-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: "2023-04-08T04:20:26Z"
    message: VolumeSnapshot/pg-cluster-postgresql-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. First, 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=pg-cluster
   
   kubectl delete volumesnapshot -l app.kubernetes.io/instance=pg-cluster

Result

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