Configure a reverse migration schedule

In case of a disaster, where one of your Kubernetes clusters is down and inaccessible, you can failover the applications running on it to an operational Kubernetes cluster. After your original source cluster is accessible again, you can failback your application to it. However, if the destination cluster has been running applications for some time, it is possible that the state of your application on the destination cluster differs from your source cluster. This is because new resources are created, or the data in stateful applications has changed on your destination cluster.

Portworx, Inc. recommends reverse syncing your source and destination clusters before failing back your applications, so that you have the most up-to-date applications on your original source cluster. This means creating a ClusterPair from your destination to source cluster, then creating a migration schedule to migrate resources from your destination to the source cluster using that ClusterPair. As both of your clusters are accessible, follow the instructions on this page to configure a reverse migration schedule.

Generate a reverse ClusterPair

1. Generate a reverse ClusterPair on your source cluster. Run the following command on the source cluster by specifying the <your-clusterpair-name> and <migrationnamespace> to create a ClusterPair and save the resulting spec to a file named reverse-clusterpair.yaml:

   • <you-remote-cluster>: is the name of the Kubernetes object that will be created on the destination cluster representing the pair relationship.

   • <migrationnamespace>: is the name of the Kubernetes namespace on the destination cluster that you want to migrate to the source cluster.

     storkctl generate clusterpair -n <migrationnamespace> <your-clusterpair-name> -o yaml > reverse-clusterpair.yaml

2. Remove the options section from the reverse-clusterpair.yaml file:

   options:
     <insert_storage_options_here>: ""

3. Copy the reverse-clusterpair.yaml file to your destination cluster and apply it using the following command:

   kubectl create -f reverse-clusterpair.yaml

4. Check the status of the pairing on the destination cluster:

   storkctl get clusterpair -n <migrationnamespace>

   NAME                       STORAGE-STATUS   SCHEDULER-STATUS   CREATED
   <your-clusterpair-name>      NotProvided      Ready              30 Nov 22 22:59 UTC

   On a successful pairing you will see the scheduler status as Ready and storage status as NotProvided.

Configure a reverse migration schedule

1. Create a schedule policy on your destination cluster using the instructions in the Create a schedule policy section.

2. Copy and paste the following spec into a file called reverse-migrationschedule.yaml on your destination cluster:

   apiVersion: stork.libopenstorage.org/v1alpha1
   kind: MigrationSchedule
   metadata:
     name: reversemigrationschedule
     namespace: <migrationnamespace> 
   spec:
     template:
       spec:
         clusterPair: <your-clusterpair-name>
         includeResources: true
         startApplications: false
         includeVolumes: false
         namespaces:
         - <migrationnamespace>
     schedulePolicyName: <your-schedule-policy>
     suspend: true

   NOTE: As the suspend parameter is set to true, this migration schedule will not be active.

3. Apply your reverse-migrationschedule.yaml on your destination cluster:

   kubectl apply -f reverse-migrationschedule.yaml

   This migration schedule will be in suspended state, and you will need to activate it before failing back your application.