Switch over a MongoDB cluster

You can initiate a switchover for a MongoDB ReplicaSet. Then KubeBlocks modifies the instance roles.

Before you start

• Make sure the cluster is running normally.

• Check whether the following role probe parameters exist to verify whether the role probe is enabled.

  kubectl get cd mongodb -o yaml
  >
  probes:
    roleProbe:
      failureThreshold: 3
      periodSeconds: 2
      timeoutSeconds: 2

Initiate the switchover

You can switch over a secondary of a MongoDB ReplicaSet to the primary role, and the former primary instance to a secondary.

kbcli

• Switchover with no primary instance specified

  kbcli cluster promote mycluster -n demo

• Switchover with a specified new primary instance

  kbcli cluster promote mycluster --instance='mycluster-mongodb-2' -n demo

• If there are multiple components, you can use --components to specify a component.

  kbcli cluster promote mycluster --instance='mycluster-mongodb-2' --components='mongodb' -n demo

kubectl

The value of instanceName decides whether a new primary instance is specified for the switchover.

• Switchover with no specified primary instance

  kubectl apply -f -<<EOF
  apiVersion: apps.kubeblocks.io/v1alpha1
  kind: OpsRequest
  metadata:
    name: mycluster-switchover-jhkgl
    namespace: demo
  spec:
    clusterRef: mycluster
    type: Switchover
    switchover:
    - componentName: mongodb
      instanceName: '*'
  >>

• Switchover with a specified new primary instance

  kubectl apply -f -<<EOF
  apiVersion: apps.kubeblocks.io/v1alpha1
  kind: OpsRequest
  metadata:
    name: mycluster-switchover-jhkgl
    namespace: demo
  spec:
    clusterRef: mycluster
    type: Switchover
    switchover:
    - componentName: mongodb
      instanceName: 'mycluster-mongodb-2'
  >>

Verify the switchover

Check the instance status to verify whether the switchover is performed successfully.

kbcli

kbcli cluster list-instances -n demo

kubectl

kubectl get pods -n demo

Handle an exception

If an error occurs, refer to Handle an exaception to troubleshoot the operation.