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Version: 3.3

Failover an application

In the event of a disaster, when one of your Kubernetes clusters becomes inaccessible, you have the option to failover the applications running on it to an operational Kubernetes cluster.

The following considerations are used in the examples on this page. Update them to the appropriate values for your environment:

  • Source Cluster is the Kubernetes cluster which is down and where your applications were originally running.
  • Destination Cluster is the Kubernetes cluster where the applications will be failed over to.
  • The Zookeeper application is being failed over to the destination cluster.

Follow the instructions on this page to perform a failover of your applications to the destination cluster. These instructions apply to both scenarios, whether it is a controlled failover or a disaster recovery.

Prerequisites​

  • You must ensure that Stork version 24.2.0 or newer is installed on both the source and destination clusters.

    note

    If you are using a Stork version prior to 24.2.0, then you can follow this procedure to perform a failover.

  • For operators deployed from the OpenShift OperatorHub:

    • Ensure that the operator is deployed on both the source and the destination clusters in the application namespace.
    • Ensure that the migration schedule is created with the --exclude-resource-types flag to exclude operator-related resources, as shown in the following example: 
      storkctl create migrationschedule -c cluster-pair -n zookeeper migration-schedule --exclude-resource-types ClusterServiceVersion,operatorconditions,OperatorGroup,InstallPlan,Subscription --exclude-selectors olm.managed=true
    • Ensure that the operator and applications are in scaled down state on the source cluster. Stork will leverage spec.replicas from most of the standard Kubernetes controllers such as Deployments, StatefulSets, and so on. However, for applications managed by an Operator, an ApplicationRegistration CR needs to be created which provides Stork with the necessary information required to perform a scale down of the application. For more information, see the Application Registration document.

Perform failover​

In the event of a disaster, you can migrate an application or workload from the source cluster to destination cluster by running the storkctl perform failover command.

You can include or exclude a subset of namespaces for migration by using one of the following flags:

  • --include-namespaces - Use this flag to include a subset of namespaces for the migration.
  • --exclude-namespaces - Use this flag to exclude a subset of namespaces for the migration.

The --include-namespaces and --exclude-namespaces flags are mutually exclusive.

Are your clusters paired in a unidirectional manner? (Click to expand for more details)
If yes, you must use the --skip-source-operations flag to skip the source cluster operations.

To start the failover operation, run the following command in the destination cluster:

storkctl perform failover -m <migration-schedule> -n <migration-schedule-namespace>

If the last migration status is in the PartialSuccess state, you'll be prompted to proceed with the failover operation. To bypass this prompt, use the --force flag.

Example:

storkctl perform failover -m migration-schedule -n zookeeper
Started failover for MigrationSchedule zookeeper/migration-schedule
To check failover status use the command : `storkctl get failover failover-migration-schedule-2024-05-20-140139 -n zookeeper`

Check failover status​

Run the following command to check the status of the failover operation. You can refer to the above section to get the value of failover-action-name.

storkctl get failover <failover-action-name> -n <migration-schedule-namespace>

Example:

storkctl get failover failover-migration-schedule-2024-05-20-140139 -n zookeeper
NAME                                    CREATED               STAGE       STATUS       MORE INFO
failover-migration-schedule-2024-05-20-140139       20 May 24 14:02 UTC   Completed   Successful   Scaled up Apps in : 1/1 namespaces

If the status is failed, you can use the following command to get more information about the failure:

kubectl describe actions <failover-action-name> -n <migration-schedule-namespace>

Verify volumes and Kubernetes resources are migrated​

To verify the volumes and Kubernetes resources that are migrated to the destination cluster, run the following command:

kubectl get all -n <migration-schedule-namespace>

Example:

kubectl get all -n zookeeper
NAME                     READY   STATUS    RESTARTS   AGE
pod/zk-544ffcc474-6gx64   1/1     Running   0          18h

NAME                 TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)    AGE
service/zk-service   ClusterIP   10.233.22.60   <none>        3306/TCP   18h

NAME                 READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/zk   1/1     1            1           18h

NAME                            DESIRED   CURRENT   READY   AGE
replicaset.apps/zk-544ffcc474   1         1         1       18h