KubeBlocks
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KubeBlocks for MongoDB

Cluster Management

Create and connect
Scale
Expand volume
Restart
Stop/Start
Switchover
Delete protection

Configuration

Configure cluster parameters
  1. Vertical scaling
    1. Before you start
    2. Steps
  2. Horizontal scaling
    1. Before you start
    2. Steps
    3. Handle the snapshot exception

Scale a MongoDB cluster

You can scale a MongoDB 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.

kubectl get cluster mycluster -n demo
>
NAME        CLUSTER-DEFINITION   VERSION       TERMINATION-POLICY   STATUS    AGE
mycluster   mongodb              mongodb-5.0   Delete               Running   27m

kbcli cluster list mycluster -n demo
>
NAME             NAMESPACE        CLUSTER-DEFINITION    VERSION            TERMINATION-POLICY        STATUS         CREATED-TIME
mycluster        demo             mongodb               mongodb-5.0        Delete                    Running        Apr 10,2023 16:20 UTC+0800

Steps

  1. 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:
  clusterName: mycluster
  type: VerticalScaling
  verticalScaling:
  - componentName: mongodb
    requests:
      memory: "2Gi"
      cpu: "1"
    limits:
      memory: "4Gi"
      cpu: "2"
EOF

  2. 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 to the vertical scaling operation, you can troubleshoot with kubectl describe ops -n demo command to view the events of this operation.

  3. Check whether the corresponding resources change.

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

  1. 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.

    kubectl edit cluster mycluster -n demo

    Edit the value of spec.componentSpecs.resources.

    ...
spec:
  affinity:
    podAntiAffinity: Preferred
    topologyKeys:
    - kubernetes.io/hostname
  clusterDefinitionRef: mongodb
  clusterVersionRef: mongodb-5.0
  componentSpecs:
  - componentDefRef: mongodb
    enabledLogs:
    - running
    disableExporter: true
    name: mongodb
    replicas: 2
    resources: # Change values of resources
      limits:
        cpu: "2"
        memory: 4Gi
      requests:
        cpu: "1"
        memory: 2Gi

  2. Check whether the corresponding resources change.

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

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

    kbcli cluster vscale mycluster -n demo --components=mongodb --cpu=500m --memory=500Mi
    • --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.

    • 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        mongodb              mongodb-5.0      Delete               Running   Apr 26,2023 11:50 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 the normal instances number is less than the total instance number or the leader 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.

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.

  1. 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

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](./../user_docs/maintenance/scale//horizontal-scale) for more details and examples.

Before you start

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

kubectl get cluster mycluster -n demo
>
NAME        CLUSTER-DEFINITION   VERSION       TERMINATION-POLICY     STATUS    AGE
mycluster   mongodb              mongodb-5.0   Delete                 Running   47m

kbcli cluster list mycluster -n demo
>
NAME          NAMESPACE     CLUSTER-DEFINITION    VERSION          TERMINATION-POLICY        STATUS         CREATED-TIME
mycluster     demo          mongodb               mongodb-5.0      Delete                    Running        April 26,2023 12:00 UTC+0800

Steps

  1. 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: mongo-horizontalscaling
  namespace: default
spec:
  clusterName: mycluster
  type: HorizontalScaling
  horizontalScaling:
  - componentName: mongodb
    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: mongo-horizontalscaling
  namespace: default
spec:
  clusterName: mycluster
  type: HorizontalScaling
  horizontalScaling:
  - componentName: mongodb
    scaleIn:
      replicaChanges: 2
EOF

  2. 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.

  3. Check whether the corresponding resources change.

    kubectl describe cluster mycluster -n demo

  1. 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

    Edit the value of spec.componentSpecs.replicas.

    ...
spec:
  clusterDefinitionRef: mongo
  clusterVersionRef: mongodb-5.0
  componentSpecs:
  - name: mongo
    componentDefRef: mongo
    replicas: 4 # Change this value
...

  2. Check whether the corresponding resources change.

    kubectl describe cluster mycluster -n demo

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

    kbcli cluster hscale mycluster -n demo --components="mongodb" --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.

    • 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 status.

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

  3. 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

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/mycluster-mongodb-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=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.

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