MTC workflow

You can migrate Kubernetes resources, persistent volume data, and internal container images to OKD 4.8 by using the Migration Toolkit for Containers (MTC) web console or the Kubernetes API.

MTC migrates the following resources:

  • A namespace specified in a migration plan.

  • Namespace-scoped resources: When the MTC migrates a namespace, it migrates all the objects and resources associated with that namespace, such as services or pods. Additionally, if a resource that exists in the namespace but not at the cluster level depends on a resource that exists at the cluster level, the MTC migrates both resources.

    For example, a security context constraint (SCC) is a resource that exists at the cluster level and a service account (SA) is a resource that exists at the namespace level. If an SA exists in a namespace that the MTC migrates, the MTC automatically locates any SCCs that are linked to the SA and also migrates those SCCs. Similarly, the MTC migrates persistent volume claims that are linked to the persistent volumes of the namespace.

    Cluster-scoped resources might have to be migrated manually, depending on the resource.

  • Custom resources (CRs) and custom resource definitions (CRDs): MTC automatically migrates CRs and CRDs at the namespace level.

Migrating an application with the MTC web console involves the following steps:

  1. Install the Migration Toolkit for Containers Operator on all clusters.

    You can install the Migration Toolkit for Containers Operator in a restricted environment with limited or no internet access. The source and target clusters must have network access to each other and to a mirror registry.

  2. Configure the replication repository, an intermediate object storage that MTC uses to migrate data.

    The source and target clusters must have network access to the replication repository during migration. In a restricted environment, you can use Multi-Cloud Object Gateway (MCG). If you are using a proxy server, you must configure it to allow network traffic between the replication repository and the clusters.

  3. Add the source cluster to the MTC web console.

  4. Add the replication repository to the MTC web console.

  5. Create a migration plan, with one of the following data migration options:

    • Copy: MTC copies the data from the source cluster to the replication repository, and from the replication repository to the target cluster.

      If you are using direct image migration or direct volume migration, the images or volumes are copied directly from the source cluster to the target cluster.

      migration PV copy
    • Move: MTC unmounts a remote volume, for example, NFS, from the source cluster, creates a PV resource on the target cluster pointing to the remote volume, and then mounts the remote volume on the target cluster. Applications running on the target cluster use the same remote volume that the source cluster was using. The remote volume must be accessible to the source and target clusters.

      Although the replication repository does not appear in this diagram, it is required for migration.

      migration PV move
  6. Run the migration plan, with one of the following options:

    • Stage copies data to the target cluster without stopping the application.

      A stage migration can be run multiple times so that most of the data is copied to the target before migration. Running one or more stage migrations reduces the duration of the cutover migration.

    • Cutover stops the application on the source cluster and moves the resources to the target cluster.

      Optional: You can clear the Halt transactions on the source cluster during migration checkbox.

OCP 3 to 4 App migration

About MTC custom resources

The Migration Toolkit for Containers (MTC) creates the following custom resources (CRs):