Schedule migrations for synchronous DR in OpenShift vSphere

Summary and Key concepts

Summary

This article explains the process of creating and scheduling periodic namespace migrations in a Portworx cluster stretched across source and destination clusters, managed by Stork. By configuring a migration schedule policy on the source cluster, users can specify regular intervals for migrating Kubernetes resources while excluding volumes, as the data is already accessible across clusters. The guide includes creating a MigrationSchedule specification, applying it to the source cluster, and monitoring migration progress. Important flags include autoSuspend to automate disaster recovery handling. Additional guidance is provided on scaling down applications to avoid conflicts during migration.

Kubernetes Concepts

• Namespaces: Used to organize resources for migration between clusters and specify which namespaces should be included in the migration.
• StorageClass: Defines storage parameters, especially useful in the context of specifying storage settings in PVCs associated with the migration process.
• PersistentVolumeClaim (PVC): Requests storage based on the StorageClass used; PVCs are referenced within the migration schedule.

Portworx Concepts

• ClusterPair: Configures the connection between source and destination clusters, facilitating resource migration without needing volume data transfer.

• Stork: A Portworx scheduler for migrating resources and managing disaster recovery in stretched clusters.

• MigrationSchedule: Defines periodic migration schedules to transfer resources between clusters based on specified policies and intervals.

• SchedulePolicy: Defines interval-based policies for scheduling migrations, which are applied to MigrationSchedule objects for regular namespace migrations.

• ApplicationRegistration: Custom Resource (CR) used to define scaling behaviors for operator-managed applications, allowing controlled scale-down during migration.

Once your source and destination clusters are paired, you need to create a schedule to migrate one or more namespaces periodically. Because you have only one Portworx cluster stretched across your source and destination clusters, you will only migrate OpenShift resources and not your volumes.

note

If you are using Stork version 24.2.0 or later, when you create a migration schedule in the source cluster, Stork automatically creates a corresponding migration schedule in the destination cluster. This migration schedule is used as a reference during the failover operation, and you must not manipulate this migration schedule on the destination cluster.

Create a schedule policy on your source cluster

You have two options for creating a schedule policy:

1. Use the storkctl create migrationschedule command with the required flags. For more details and examples, refer to the Create schedule policy with storkctl section.

2. Alternatively, to schedule a migration, you must define a schedule policy. You can select from two types of policies:

   • SchedulePolicy: A cluster-scoped policy that applies to the entire cluster.
   • NamespacedSchedulePolicy: A namespace-scoped policy that applies only to the specified namespace in the policy spec.

Follow the steps below to create a schedule policy on your source cluster:

1. Create a spec file using one of the following methods.

   • For SchedulePolicy, create the following spec file:

     apiVersion: stork.libopenstorage.org/v1alpha1
     kind: SchedulePolicy
     metadata:
       name: <your-schedule-policy>
     policy:
       interval:
         intervalMinutes: 30   

     For a list of parameters that you can use to create a schedule policy, see the Schedule Policy page.

   • For NamespacedSchedulePolicy, create the following spec file:

     apiVersion: stork.libopenstorage.org/v1alpha1
     kind: NamespacedSchedulePolicy
     metadata:
       name: <your-schedule-policy>
       namespace: <migrationnamespace>
     policy:
       interval:
         intervalMinutes: 30  

     For a list of parameters that you can use to create a namespaced policy, you can use the fields described on the Schedule Policy page, replacing SchedulePolicy with NamespacedSchedulePolicy.

   • You can also use the schedule policies that are installed by default. Run the storkctl get schedulepolicy command to get the list of these policies, then specify a policy name in the next section for creating a migration schedule. You can skip the next step if you are using the default policies, as they are already applied to your cluster.

2. Apply your policy on the source cluster:

   oc apply -f <your-schedule-policy>.yaml

3. Verify if the policy has been created:

   storkctl get schedulepolicy <your-schedule-policy>

   NAME                      INTERVAL-MINUTES    DAILY     WEEKLY             MONTHLY
   <your-schedule-policy>          30             N/A       N/A                N/A

Create a migration schedule on your source cluster

Once a policy has been created, you can use it to schedule migrations.

note

For operators deployed from the OpenShift OperatorHub, create a migration schedule with the --exclude-resource-types flag to exclude operator-related resources, as shown in the following example:

storkctl create migrationschedule -c <cluster-pair> --namespaces <namespace> <migration-schedule> --exclude-resource-types ClusterServiceVersion,operatorconditions,OperatorGroup,InstallPlan,Subscription --exclude-selectors olm.managed=true`

You have two options for creating a migration schedule:

• Run the storkctl create migrationschedule command-line tool the along with the required flags. See Create migration schedule with storkctl topic for more information about the commands with examples, or

• Perform the following steps on your source cluster:

  1. Copy and paste the following spec into a file called migrationschedule.yaml. Modify the following spec to use a different migration schedule name and/or namespace. Ensure that the clusterPair name is correct.

     apiVersion: stork.libopenstorage.org/v1alpha1
     kind: MigrationSchedule
     metadata:
       name: migrationschedule
       namespace: <migrationnamespace> 
     spec:
       template:
         spec:
           clusterPair: <your-clusterpair-name>
           includeResources: true
           startApplications: false
           includeVolumes: false
           namespaces:
           - <app-namespace1>
           - <app-namespace2>
       schedulePolicyName: <your-schedule-policy>
       suspend: false
       autoSuspend: true
  note

  • The option startApplications must be set to false in the spec to ensure that the application pods do not start on the remote cluster when the Kubernetes resources are being migrated.
  • The option includeVolumes is set to false because the volumes are already present on the destination cluster as this is a single Portworx cluster.
  • With Stork 23.2 or newer, you can set the autoSuspend flag to true, as shown in the above spec. In case of a disaster, this will suspend the DR migration schedules automatically on your source cluster, and you will be able to migrate your application to an active Kubernetes cluster. If you are using an older version of Stork, refer to the Failover an application page for achieving failover for your application.
  2. Apply your migrationschedule.yaml by entering the following command:

  oc apply -f migrationschedule.yaml

  If the policy name is missing or invalid there will be events logged against the schedule object. Success and failures of the migrations created by the schedule will also result in events being logged against the object. These events can be seen by running a oc describe command on the object.

• Perform the following steps on your source cluster:

  1. Copy and paste the following spec into a file called migrationschedule.yaml. Modify the following spec to use a different migration schedule name and/or namespace. Ensure that the clusterPair name is correct.

     apiVersion: stork.libopenstorage.org/v1alpha1
     kind: MigrationSchedule
     metadata:
       name: migrationschedule
       namespace: <migrationnamespace> 
     spec:
       template:
         spec:
           clusterPair: <your-clusterpair-name>
           includeResources: true
           startApplications: false
           includeVolumes: false
           namespaces:
           - <app-namespace1>
           - <app-namespace2>
       schedulePolicyName: <your-schedule-policy>
       suspend: false
       autoSuspend: true

note

• The option startApplications must be set to false in the spec to ensure that the application pods do not start on the remote cluster when the Kubernetes resources are being migrated.
• The option includeVolumes is set to false because the volumes are already present on the destination cluster as this is a single Portworx cluster.
• With Stork 23.2 or newer, you can set the autoSuspend flag to true, as shown in the above spec. In case of a disaster, this will suspend the DR migration schedules automatically on your source cluster, and you will be able to migrate your application to an active Kubernetes cluster. If you are using an older version of Stork, refer to the Failover an application page for achieving failover for your application.

2. Apply your migrationschedule.yaml by entering the following command:

oc apply -f migrationschedule.yaml

If the policy name is missing or invalid there will be events logged against the schedule object. Success and failures of the migrations created by the schedule will also result in events being logged against the object. These events can be seen by running a oc describe command on the object.

Check your migration status

1. Run the following command on your source cluster to check the status of your migration:

   storkctl get migration -n <migrationnamespace>

   NAMESPACE                      NAME                                                                CLUSTERPAIR                STAGE   STATUS       VOLUMES   RESOURCES   CREATED               ELAPSED                          TOTAL BYTES TRANSFERRED
   bidirectional-clusterpair-ns   <your-app>-migration-schedule-interval-interval-2023-08-28-015917   birectional-cluster-pair   Final   Successful   1/1       4/4         27 Aug 23 19:59 MDT   Volumes (33s) Resources (1m2s)   4096
   • The output above indicates a successful migration in the Status column. It also provides a list of migration objects along with timestamps associated with your migration.
   • You can also run the oc describe migration -n <migrationnamespace> to check details about specific migrations.

2. Verify your application and associated resources have been migrated by running the following command on your destination cluster:

   oc get all -n zookeeper

     NAME                      TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)    AGE
     service/zk-service        ClusterIP   10.xxx.xx.68   <none>        xxxx/TCP   2m13s
   
     NAME                       READY   UP-TO-DATE   AVAILABLE   AGE
     deployment.apps/zk         0/0     0            0           2m13s
   
     NAME                               DESIRED   CURRENT   READY   AGE
     replicaset.apps/zk-59d878d987      0         0         0       2m13s

This confirms that the respective namespace has been created and the applications (for example, Zookeeper) are installed. However, the application pods will not be not running because they are running on the source cluster.

note

As part of every Migration, Stork will also migrate the Kubernetes resources associated with your applications. For a successful migration, these applications need to be in a scaled down state on the destination side so that subsequent migrations from the same schedule can run to completion. To achieve this 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. Refer to the ApplicationRegistrations page for more details.