Advanced migration options

You can automate your migrations and modify the MigPlan and MigrationController custom resources in order to perform large-scale migrations and to improve performance.

Terminology

1 Called the target cluster in the MTC web console.

Migrating an application from on-premises to a cloud-based cluster

You can migrate from a source cluster that is behind a firewall to a cloud-based destination cluster by establishing a network tunnel between the two clusters. The crane tunnel-api command establishes such a tunnel by creating a VPN tunnel on the source cluster and then connecting to a VPN server running on the destination cluster. The VPN server is exposed to the client using a load balancer address on the destination cluster.

A service created on the destination cluster exposes the source cluster’s API to MTC, which is running on the destination cluster.

Prerequisites

• The system that creates the VPN tunnel must have access and be logged in to both clusters.

• It must be possible to create a load balancer on the destination cluster. Refer to your cloud provider to ensure this is possible.

• Have names prepared to assign to namespaces, on both the source cluster and the destination cluster, in which to run the VPN tunnel. These namespaces should not be created in advance. For information about namespace rules, see https://kubernetes.io/docs/concepts/overview/working-with-objects/names/#dns-subdomain-names.

• When connecting multiple firewall-protected source clusters to the cloud cluster, each source cluster requires its own namespace.

• OpenVPN server is installed on the destination cluster.

• OpenVPN client is installed on the source cluster.

• When configuring the source cluster in MTC, the API URL takes the form of https://proxied-cluster.<namespace>.svc.cluster.local:8443.

  • If you use the API, see Create a MigCluster CR manifest for each remote cluster.

  • If you use the MTC web console, see Migrating your applications using the MTC web console.

• The MTC web console and Migration Controller must be installed on the target cluster.

Procedure

1. Install the crane utility:

   $ podman cp $(podman create registry.redhat.io/rhmtc/openshift-migration-controller-rhel8:v1.7.0):/crane ./

2. Log in remotely to a node on the source cluster and a node on the destination cluster.

3. Obtain the cluster context for both clusters after logging in:

   $ oc config view

4. Establish a tunnel by entering the following command on the command system:

   $ crane tunnel-api [--namespace <namespace>] \
         --destination-context <destination-cluster> \
         --source-context <source-cluster>

   If you don’t specify a namespace, the command uses the default value openvpn.

   For example:

   $ crane tunnel-api --namespace my_tunnel \
         --destination-context openshift-migration/c131-e-us-east-containers-cloud-ibm-com/admin \
         --source-context default/192-168-122-171-nip-io:8443/admin

   See all available parameters for the crane tunnel-api command by entering crane tunnel-api —help.

   The command generates TSL/SSL Certificates. This process might take several minutes. A message appears when the process completes.

   The OpenVPN server starts on the destination cluster and the OpenVPN client starts on the source cluster.

   After a few minutes, the load balancer resolves on the source node.

   You can view the log for the OpenVPN pods to check the status of this process by entering the following commands with root privileges: # oc get po -n <namespace> Example output NAME READY STATUS RESTARTS AGE <pod_name> 2/2 Running 0 44s # oc logs -f -n <namespace> <pod_name> -c openvpn When the address of the load balancer is resolved, the message Initialization Sequence Completed appears at the end of the log.

5. On the OpenVPN server, which is on a destination control node, verify that the openvpn service and the proxied-cluster service are running:

   $ oc get service -n <namespace>

6. On the source node, get the service account (SA) token for the migration controller:

   # oc sa get-token -n openshift-migration migration-controller

7. Open the MTC web console and add the source cluster, using the following values:

   • Cluster name: The source cluster name.

   • URL: proxied-cluster.<namespace>.svc.cluster.local:8443. If you did not define a value for <namespace>, use openvpn.

   • Service account token: The token of the migration controller service account.

   • Exposed route host to image registry: proxied-cluster.<namespace>.svc.cluster.local:5000. If you did not define a value for <namespace>, use openvpn.

After MTC has successfully validated the connection, you can proceed to create and run a migration plan. The namespace for the source cluster should appear in the list of namespaces.

Additional resources

• For information about creating a MigCluster CR manifest for each remote cluster, see Migrating an application by using the MTC API.

• For information about adding a cluster using the web console, see Migrating your applications by using the MTC web console

Migrating applications by using the command line

You can migrate applications with the MTC API by using the command line interface (CLI) in order to automate the migration.

Migration prerequisites

• You must be logged in as a user with cluster-admin privileges on all clusters.

Direct image migration

• You must ensure that the secure internal registry of the source cluster is exposed.

• You must create a route to the exposed registry.

Direct volume migration

• If your clusters use proxies, you must configure an Stunnel TCP proxy.

Internal images

• If your application uses internal images from the openshift namespace, you must ensure that the required versions of the images are present on the target cluster.

  You can manually update an image stream tag in order to use a deprecated OKD 3 image on an OKD 4.10 cluster.

Clusters

• The source cluster must be upgraded to the latest MTC z-stream release.

• The MTC version must be the same on all clusters.

Network

• The clusters have unrestricted network access to each other and to the replication repository.

• If you copy the persistent volumes with move, the clusters must have unrestricted network access to the remote volumes.

• You must enable the following ports on an OKD 3 cluster:

  • 8443 (API server)

  • 443 (routes)

  • 53 (DNS)

• You must enable the following ports on an OKD 4 cluster:

  • 6443 (API server)

  • 443 (routes)

  • 53 (DNS)

• You must enable port 443 on the replication repository if you are using TLS.

Persistent volumes (PVs)

• The PVs must be valid.

• The PVs must be bound to persistent volume claims.

• If you use snapshots to copy the PVs, the following additional prerequisites apply:

  • The cloud provider must support snapshots.

  • The PVs must have the same cloud provider.

  • The PVs must be located in the same geographic region.

  • The PVs must have the same storage class.

Creating a registry route for direct image migration

For direct image migration, you must create a route to the exposed internal registry on all remote clusters.

Prerequisites

• The internal registry must be exposed to external traffic on all remote clusters.

  The OKD 4 registry is exposed by default.

  The OKD 3 registry must be exposed manually.

Procedure

• To create a route to an OKD 3 registry, run the following command:

  $ oc create route passthrough --service=docker-registry -n default

• To create a route to an OKD 4 registry, run the following command:

  $ oc create route passthrough --service=image-registry -n openshift-image-registry

Configuring proxies

For OKD 4.1 and earlier versions, you must configure proxies in the MigrationController custom resource (CR) manifest after you install the Migration Toolkit for Containers Operator because these versions do not support a cluster-wide proxy object.

For OKD 4.2 to 4.10, the Migration Toolkit for Containers (MTC) inherits the cluster-wide proxy settings. You can change the proxy parameters if you want to override the cluster-wide proxy settings.

You must configure the proxies to allow the SPDY protocol and to forward the Upgrade HTTP header to the API server. Otherwise, an Upgrade request required error is displayed. The MigrationController CR uses SPDY to run commands within remote pods. The Upgrade HTTP header is required in order to open a websocket connection with the API server.

Direct volume migration

If you are performing a direct volume migration (DVM) from a source cluster behind a proxy, you must configure an Stunnel proxy. Stunnel creates a transparent tunnel between the source and target clusters for the TCP connection without changing the certificates.

DVM supports only one proxy. The source cluster cannot access the route of the target cluster if the target cluster is also behind a proxy.

Prerequisites

• You must be logged in as a user with cluster-admin privileges on all clusters.

Procedure

1. Get the MigrationController CR manifest:

   $ oc get migrationcontroller <migration_controller> -n openshift-migration

2. Update the proxy parameters:

   apiVersion: migration.openshift.io/v1alpha1
   kind: MigrationController
   metadata:
     name: <migration_controller>
     namespace: openshift-migration
   ...
   spec:
     stunnel_tcp_proxy: http://<username>:<password>@<ip>:<port> (1)
     httpProxy: http://<username>:<password>@<ip>:<port> (2)
     httpsProxy: http://<username>:<password>@<ip>:<port> (3)
     noProxy: example.com (4)

   1	Stunnel proxy URL for direct volume migration.
   2	Proxy URL for creating HTTP connections outside the cluster. The URL scheme must be http.
   3	Proxy URL for creating HTTPS connections outside the cluster. If this is not specified, then httpProxy is used for both HTTP and HTTPS connections.
   4	Comma-separated list of destination domain names, domains, IP addresses, or other network CIDRs to exclude proxying.

   Preface a domain with . to match subdomains only. For example, .y.com matches x.y.com, but not y.com. Use * to bypass proxy for all destinations. If you scale up workers that are not included in the network defined by the networking.machineNetwork[].cidr field from the installation configuration, you must add them to this list to prevent connection issues.

   This field is ignored if neither the httpProxy nor the httpsProxy field is set.

3. Save the manifest as migration-controller.yaml.

4. Apply the updated manifest:

   $ oc replace -f migration-controller.yaml -n openshift-migration

Migrating an application by using the MTC API

You can migrate an application from the command line by using the Migration Toolkit for Containers (MTC) API.

Procedure

1. Create a MigCluster CR manifest for the host cluster:

   $ cat << EOF | oc apply -f -
   apiVersion: migration.openshift.io/v1alpha1
   kind: MigCluster
   metadata:
     name: <host_cluster>
     namespace: openshift-migration
   spec:
     isHostCluster: true
   EOF

2. Create a Secret object manifest for each remote cluster:

   $ cat << EOF | oc apply -f -
   apiVersion: v1
   kind: Secret
   metadata:
     name: <cluster_secret>
     namespace: openshift-config
   type: Opaque
   data:
     saToken: <sa_token> (1)
   EOF

   1	Specify the base64-encoded migration-controller service account (SA) token of the remote cluster. You can obtain the token by running the following command:

   $ oc sa get-token migration-controller -n openshift-migration | base64 -w 0

3. Create a MigCluster CR manifest for each remote cluster:

   $ cat << EOF | oc apply -f -
   apiVersion: migration.openshift.io/v1alpha1
   kind: MigCluster
   metadata:
     name: <remote_cluster> (1)
     namespace: openshift-migration
   spec:
     exposedRegistryPath: <exposed_registry_route> (2)
     insecure: false (3)
     isHostCluster: false
     serviceAccountSecretRef:
       name: <remote_cluster_secret> (4)
       namespace: openshift-config
     url: <remote_cluster_url> (5)
   EOF

   1	Specify the Cluster CR of the remote cluster.
   2	Optional: For direct image migration, specify the exposed registry route.
   3	SSL verification is enabled if false. CA certificates are not required or checked if true.
   4	Specify the Secret object of the remote cluster.
   5	Specify the URL of the remote cluster.

4. Verify that all clusters are in a Ready state:

   $ oc describe cluster <cluster>

5. Create a Secret object manifest for the replication repository:

   $ cat << EOF | oc apply -f -
   apiVersion: v1
   kind: Secret
   metadata:
     namespace: openshift-config
     name: <migstorage_creds>
   type: Opaque
   data:
     aws-access-key-id: <key_id_base64> (1)
     aws-secret-access-key: <secret_key_base64> (2)
   EOF

   1	Specify the key ID in base64 format.
   2	Specify the secret key in base64 format.

   AWS credentials are base64-encoded by default. For other storage providers, you must encode your credentials by running the following command with each key:

   $ echo -n "<key>" | base64 -w 0 (1)

   1	Specify the key ID or the secret key. Both keys must be base64-encoded.

6. Create a MigStorage CR manifest for the replication repository:

   $ cat << EOF | oc apply -f -
   apiVersion: migration.openshift.io/v1alpha1
   kind: MigStorage
   metadata:
     name: <migstorage>
     namespace: openshift-migration
   spec:
     backupStorageConfig:
       awsBucketName: <bucket> (1)
       credsSecretRef:
         name: <storage_secret> (2)
         namespace: openshift-config
     backupStorageProvider: <storage_provider> (3)
     volumeSnapshotConfig:
       credsSecretRef:
         name: <storage_secret> (4)
         namespace: openshift-config
     volumeSnapshotProvider: <storage_provider> (5)
   EOF

   1	Specify the bucket name.
   2	Specify the Secrets CR of the object storage. You must ensure that the credentials stored in the Secrets CR of the object storage are correct.
   3	Specify the storage provider.
   4	Optional: If you are copying data by using snapshots, specify the Secrets CR of the object storage. You must ensure that the credentials stored in the Secrets CR of the object storage are correct.
   5	Optional: If you are copying data by using snapshots, specify the storage provider.

7. Verify that the MigStorage CR is in a Ready state:

   $ oc describe migstorage <migstorage>

8. Create a MigPlan CR manifest:

   $ cat << EOF | oc apply -f -
   apiVersion: migration.openshift.io/v1alpha1
   kind: MigPlan
   metadata:
     name: <migplan>
     namespace: openshift-migration
   spec:
     destMigClusterRef:
       name: <host_cluster>
       namespace: openshift-migration
     indirectImageMigration: true (1)
     indirectVolumeMigration: true (2)
     migStorageRef:
       name: <migstorage> (3)
       namespace: openshift-migration
     namespaces:
       - <source_namespace_1> (4)
       - <source_namespace_2>
       - <source_namespace_3>:<destination_namespace> (5)
     srcMigClusterRef:
       name: <remote_cluster> (6)
       namespace: openshift-migration
   EOF

   1	Direct image migration is enabled if false.
   2	Direct volume migration is enabled if false.
   3	Specify the name of the MigStorage CR instance.
   4	Specify one or more source namespaces. By default, the destination namespace has the same name.
   5	Specify a destination namespace if it is different from the source namespace.
   6	Specify the name of the source cluster MigCluster instance.

9. Verify that the MigPlan instance is in a Ready state:

   $ oc describe migplan <migplan> -n openshift-migration

10. Create a MigMigration CR manifest to start the migration defined in the MigPlan instance:

    $ cat << EOF | oc apply -f -
    apiVersion: migration.openshift.io/v1alpha1
    kind: MigMigration
    metadata:
     name: <migmigration>
     namespace: openshift-migration
    spec:
     migPlanRef:
       name: <migplan> (1)
       namespace: openshift-migration
     quiescePods: true (2)
     stage: false (3)
     rollback: false (4)
    EOF

    1	Specify the MigPlan CR name.
    2	The pods on the source cluster are stopped before migration if true.
    3	A stage migration, which copies most of the data without stopping the application, is performed if true.
    4	A completed migration is rolled back if true.

11. Verify the migration by watching the MigMigration CR progress:

    $ oc watch migmigration <migmigration> -n openshift-migration

    The output resembles the following:

    Example output

    Name:         c8b034c0-6567-11eb-9a4f-0bc004db0fbc
    Namespace:    openshift-migration
    Labels:       migration.openshift.io/migplan-name=django
    Annotations:  openshift.io/touch: e99f9083-6567-11eb-8420-0a580a81020c
    API Version:  migration.openshift.io/v1alpha1
    Kind:         MigMigration
    ...
    Spec:
     Mig Plan Ref:
       Name:       migplan
       Namespace:  openshift-migration
     Stage:        false
    Status:
     Conditions:
       Category:              Advisory
       Last Transition Time:  2021-02-02T15:04:09Z
       Message:               Step: 19/47
       Reason:                InitialBackupCreated
       Status:                True
       Type:                  Running
       Category:              Required
       Last Transition Time:  2021-02-02T15:03:19Z
       Message:               The migration is ready.
       Status:                True
       Type:                  Ready
       Category:              Required
       Durable:               true
       Last Transition Time:  2021-02-02T15:04:05Z
       Message:               The migration registries are healthy.
       Status:                True
       Type:                  RegistriesHealthy
     Itinerary:               Final
     Observed Digest:         7fae9d21f15979c71ddc7dd075cb97061895caac5b936d92fae967019ab616d5
     Phase:                   InitialBackupCreated
     Pipeline:
       Completed:  2021-02-02T15:04:07Z
       Message:    Completed
       Name:       Prepare
       Started:    2021-02-02T15:03:18Z
       Message:    Waiting for initial Velero backup to complete.
       Name:       Backup
       Phase:      InitialBackupCreated
       Progress:
         Backup openshift-migration/c8b034c0-6567-11eb-9a4f-0bc004db0fbc-wpc44: 0 out of estimated total of 0 objects backed up (5s)
       Started:        2021-02-02T15:04:07Z
       Message:        Not started
       Name:           StageBackup
       Message:        Not started
       Name:           StageRestore
       Message:        Not started
       Name:           DirectImage
       Message:        Not started
       Name:           DirectVolume
       Message:        Not started
       Name:           Restore
       Message:        Not started
       Name:           Cleanup
     Start Timestamp:  2021-02-02T15:03:18Z
    Events:
     Type    Reason   Age                 From                     Message
     ----    ------   ----                ----                     -------
     Normal  Running  57s                 migmigration_controller  Step: 2/47
     Normal  Running  57s                 migmigration_controller  Step: 3/47
     Normal  Running  57s (x3 over 57s)   migmigration_controller  Step: 4/47
     Normal  Running  54s                 migmigration_controller  Step: 5/47
     Normal  Running  54s                 migmigration_controller  Step: 6/47
     Normal  Running  52s (x2 over 53s)   migmigration_controller  Step: 7/47
     Normal  Running  51s (x2 over 51s)   migmigration_controller  Step: 8/47
     Normal  Ready    50s (x12 over 57s)  migmigration_controller  The migration is ready.
     Normal  Running  50s                 migmigration_controller  Step: 9/47
     Normal  Running  50s                 migmigration_controller  Step: 10/47

State migration

You can perform repeatable, state-only migrations by using Migration Toolkit for Containers (MTC) to migrate persistent volume claims (PVCs) that constitute an application’s state. You migrate specified PVCs by excluding other PVCs from the migration plan. Persistent volume (PV) data is copied to the target cluster. The PV references are not moved. The application pods continue to run on the source cluster. You can map the PVCs to ensure that the source and target PVCs are synchronized.

You can perform a one-time migration of Kubernetes objects that constitute an application’s state.

If you have a CI/CD pipeline, you can migrate stateless components by deploying them on the target cluster. Then you can migrate stateful components by using MTC.

You can perform a state migration between clusters or within the same cluster.

Additional resources

• See Excluding PVCs from migration to select PVCs for state migration.

• See Mapping PVCs to migrate source PV data to provisioned PVCs on the destination cluster.

• See Migrating Kubernetes objects to migrate the Kubernetes objects that constitute an application’s state.

Migration hooks

You can add up to four migration hooks to a single migration plan, with each hook running at a different phase of the migration. Migration hooks perform tasks such as customizing application quiescence, manually migrating unsupported data types, and updating applications after migration.

A migration hook runs on a source or a target cluster at one of the following migration steps:

• PreBackup: Before resources are backed up on the source cluster.

• PostBackup: After resources are backed up on the source cluster.

• PreRestore: Before resources are restored on the target cluster.

• PostRestore: After resources are restored on the target cluster.

You can create a hook by creating an Ansible playbook that runs with the default Ansible image or with a custom hook container.

Ansible playbook

The Ansible playbook is mounted on a hook container as a config map. The hook container runs as a job, using the cluster, service account, and namespace specified in the MigPlan custom resource. The job continues to run until it reaches the default limit of 6 retries or a successful completion. This continues even if the initial pod is evicted or killed.

The default Ansible runtime image is registry.redhat.io/rhmtc/openshift-migration-hook-runner-rhel7:1.7. This image is based on the Ansible Runner image and includes python-openshift for Ansible Kubernetes resources and an updated oc binary.

Custom hook container

You can use a custom hook container instead of the default Ansible image.

Writing an Ansible playbook for a migration hook

You can write an Ansible playbook to use as a migration hook. The hook is added to a migration plan by using the MTC web console or by specifying values for the spec.hooks parameters in the MigPlan custom resource (CR) manifest.

The Ansible playbook is mounted onto a hook container as a config map. The hook container runs as a job, using the cluster, service account, and namespace specified in the MigPlan CR. The hook container uses a specified service account token so that the tasks do not require authentication before they run in the cluster.

Ansible modules

You can use the Ansible shell module to run oc commands.

Example shell module

- hosts: localhost
  gather_facts: false
  tasks:
  - name: get pod name
    shell: oc get po --all-namespaces

You can use kubernetes.core modules, such as k8s_info, to interact with Kubernetes resources.

Example k8s_facts module

- hosts: localhost
  gather_facts: false
  tasks:
  - name: Get pod
    k8s_info:
      kind: pods
      api: v1
      namespace: openshift-migration
      name: "{{ lookup( 'env', 'HOSTNAME') }}"
    register: pods
  - name: Print pod name
    debug:
      msg: "{{ pods.resources[0].metadata.name }}"

You can use the fail module to produce a non-zero exit status in cases where a non-zero exit status would not normally be produced, ensuring that the success or failure of a hook is detected. Hooks run as jobs and the success or failure status of a hook is based on the exit status of the job container.

Example fail module

- hosts: localhost
  gather_facts: false
  tasks:
  - name: Set a boolean
    set_fact:
      do_fail: true
  - name: "fail"
    fail:
      msg: "Cause a failure"
    when: do_fail

Environment variables

The MigPlan CR name and migration namespaces are passed as environment variables to the hook container. These variables are accessed by using the lookup plug-in.

Example environment variables

- hosts: localhost
  gather_facts: false
  tasks:
  - set_fact:
      namespaces: "{{ (lookup( 'env', 'migration_namespaces')).split(',') }}"
  - debug:
      msg: "{{ item }}"
    with_items: "{{ namespaces }}"
  - debug:
      msg: "{{ lookup( 'env', 'migplan_name') }}"

Migration plan options

You can exclude, edit, and map components in the MigPlan custom resource (CR).

Excluding resources

You can exclude resources, for example, image streams, persistent volumes (PVs), or subscriptions, from a Migration Toolkit for Containers (MTC) migration plan to reduce the resource load for migration or to migrate images or PVs with a different tool.

By default, the MTC excludes service catalog resources and Operator Lifecycle Manager (OLM) resources from migration. These resources are parts of the service catalog API group and the OLM API group, neither of which is supported for migration at this time.

Procedure

1. Edit the MigrationController custom resource manifest:

   $ oc edit migrationcontroller <migration_controller> -n openshift-migration

2. Update the spec section by adding parameters to exclude specific resources. For those resources that do not have their own exclusion parameters, add the additional_excluded_resources parameter:

   apiVersion: migration.openshift.io/v1alpha1
   kind: MigrationController
   metadata:
     name: migration-controller
     namespace: openshift-migration
   spec:
     disable_image_migration: true (1)
     disable_pv_migration: true (2)
     additional_excluded_resources: (3)
     - resource1
     - resource2
     ...

   1	Add disable_image_migration: true to exclude image streams from the migration. imagestreams is added to the excluded_resources list in main.yml when the MigrationController pod restarts.
   2	Add disable_pv_migration: true to exclude PVs from the migration plan. persistentvolumes and persistentvolumeclaims are added to the excluded_resources list in main.yml when the MigrationController pod restarts. Disabling PV migration also disables PV discovery when you create the migration plan.
   3	You can add OKD resources that you want to exclude to the additional_excluded_resources list.

3. Wait two minutes for the MigrationController pod to restart so that the changes are applied.

4. Verify that the resource is excluded:

   $ oc get deployment -n openshift-migration migration-controller -o yaml | grep EXCLUDED_RESOURCES -A1

   The output contains the excluded resources:

   Example output

   name: EXCLUDED_RESOURCES
   value:
   resource1,resource2,imagetags,templateinstances,clusterserviceversions,packagemanifests,subscriptions,servicebrokers,servicebindings,serviceclasses,serviceinstances,serviceplans,imagestreams,persistentvolumes,persistentvolumeclaims

Mapping namespaces

If you map namespaces in the MigPlan custom resource (CR), you must ensure that the namespaces are not duplicated on the source or the destination clusters because the UID and GID ranges of the namespaces are copied during migration.

Two source namespaces mapped to the same destination namespace

spec:
  namespaces:
    - namespace_2
    - namespace_1:namespace_2

If you want the source namespace to be mapped to a namespace of the same name, you do not need to create a mapping. By default, a source namespace and a target namespace have the same name.

Incorrect namespace mapping

spec:
  namespaces:
    - namespace_1:namespace_1

Correct namespace reference

spec:
  namespaces:
    - namespace_1

Excluding persistent volume claims

You select persistent volume claims (PVCs) for state migration by excluding the PVCs that you do not want to migrate. You exclude PVCs by setting the spec.persistentVolumes.pvc.selection.action parameter of the MigPlan custom resource (CR) after the persistent volumes (PVs) have been discovered.

Prerequisites

• MigPlan CR is in a Ready state.

Procedure

• Add the spec.persistentVolumes.pvc.selection.action parameter to the MigPlan CR and set it to skip:

  apiVersion: migration.openshift.io/v1alpha1
  kind: MigPlan
  metadata:
    name: <migplan>
    namespace: openshift-migration
  spec:
  ...
    persistentVolumes:
    - capacity: 10Gi
      name: <pv_name>
      pvc:
  ...
      selection:
        action: skip

Mapping persistent volume claims

You can migrate persistent volume (PV) data from the source cluster to persistent volume claims (PVCs) that are already provisioned in the destination cluster in the MigPlan CR by mapping the PVCs. This mapping ensures that the destination PVCs of migrated applications are synchronized with the source PVCs.

You map PVCs by updating the spec.persistentVolumes.pvc.name parameter in the MigPlan custom resource (CR) after the PVs have been discovered.

Prerequisites

• MigPlan CR is in a Ready state.

Procedure

• Update the spec.persistentVolumes.pvc.name parameter in the MigPlan CR:

  apiVersion: migration.openshift.io/v1alpha1
  kind: MigPlan
  metadata:
    name: <migplan>
    namespace: openshift-migration
  spec:
  ...
    persistentVolumes:
    - capacity: 10Gi
      name: <pv_name>
      pvc:
        name: <source_pvc>:<destination_pvc> (1)

  1	Specify the PVC on the source cluster and the PVC on the destination cluster. If the destination PVC does not exist, it will be created. You can use this mapping to change the PVC name during migration.

Editing persistent volume attributes

After you create a MigPlan custom resource (CR), the MigrationController CR discovers the persistent volumes (PVs). The spec.persistentVolumes block and the status.destStorageClasses block are added to the MigPlan CR.

You can edit the values in the spec.persistentVolumes.selection block. If you change values outside the spec.persistentVolumes.selection block, the values are overwritten when the MigPlan CR is reconciled by the MigrationController CR.

Prerequisites

• MigPlan CR is in a Ready state.

Procedure

• Edit the spec.persistentVolumes.selection values in the MigPlan CR:

  apiVersion: migration.openshift.io/v1alpha1
  kind: MigPlan
  metadata:
    name: <migplan>
    namespace: openshift-migration
  spec:
    persistentVolumes:
    - capacity: 10Gi
      name: pvc-095a6559-b27f-11eb-b27f-021bddcaf6e4
      proposedCapacity: 10Gi
      pvc:
        accessModes:
        - ReadWriteMany
        hasReference: true
        name: mysql
        namespace: mysql-persistent
      selection:
        action: <copy> (1)
        copyMethod: <filesystem> (2)
        verify: true (3)
        storageClass: <gp2> (4)
        accessMode: <ReadWriteMany> (5)
      storageClass: cephfs

  1	Allowed values are move, copy, and skip. If only one action is supported, the default value is the supported action. If multiple actions are supported, the default value is copy.
  2	Allowed values are snapshot and filesystem. Default value is filesystem.
  3	The verify parameter is displayed if you select the verification option for file system copy in the MTC web console. You can set it to false.
  4	You can change the default value to the value of any name parameter in the status.destStorageClasses block of the MigPlan CR. If no value is specified, the PV will have no storage class after migration.
  5	Allowed values are ReadWriteOnce and ReadWriteMany. If this value is not specified, the default is the access mode of the source cluster PVC. You can only edit the access mode in the MigPlan CR. You cannot edit it by using the MTC web console.

Additional resources

• For details about the move and copy actions, see MTC workflow.

• For details about the skip action, see Excluding PVCs from migration.

• For details about the file system and snapshot copy methods, see About data copy methods.

Migrating Kubernetes objects

You can perform a one-time migration of Kubernetes objects that constitute an application’s state.

You add Kubernetes objects to the MigPlan CR by using one of the following options:

• Adding the Kubernetes objects to the includedResources section.

• Using the labelSelector parameter to reference labeled Kubernetes objects.

• Adding Kubernetes objects to the includedResources section and then filtering them with the labelSelector parameter, for example, Secret and ConfigMap resources with the label app: frontend.

Procedure

• Update the MigPlan CR:

  apiVersion: migration.openshift.io/v1alpha1
  kind: MigPlan
  metadata:
    name: <migplan>
    namespace: openshift-migration
  spec:
    includedResources:
    - kind: <kind> (1)
      group: ""
    - kind: <kind>
      group: ""
  ...
    labelSelector:
      matchLabels:
        <label> (2)

  1	Specify the Kubernetes object, for example, Secret or ConfigMap.
  2	Specify the label of the resources to migrate, for example, app: frontend.

Migration controller options

You can edit migration plan limits, enable persistent volume resizing, or enable cached Kubernetes clients in the MigrationController custom resource (CR) for large migrations and improved performance.

Increasing limits for large migrations

You can increase the limits on migration objects and container resources for large migrations with the Migration Toolkit for Containers (MTC).

Procedure

1. Edit the MigrationController custom resource (CR) manifest:

   $ oc edit migrationcontroller -n openshift-migration

2. Update the following parameters:

   ...
   mig_controller_limits_cpu: "1" (1)
   mig_controller_limits_memory: "10Gi" (2)
   ...
   mig_controller_requests_cpu: "100m" (3)
   mig_controller_requests_memory: "350Mi" (4)
   ...
   mig_pv_limit: 100 (5)
   mig_pod_limit: 100 (6)
   mig_namespace_limit: 10 (7)
   ...

   1	Specifies the number of CPUs available to the MigrationController CR.
   2	Specifies the amount of memory available to the MigrationController CR.
   3	Specifies the number of CPU units available for MigrationController CR requests. 100m represents 0.1 CPU units (100 * 1e-3).
   4	Specifies the amount of memory available for MigrationController CR requests.
   5	Specifies the number of persistent volumes that can be migrated.
   6	Specifies the number of pods that can be migrated.
   7	Specifies the number of namespaces that can be migrated.

3. Create a migration plan that uses the updated parameters to verify the changes.

   If your migration plan exceeds the MigrationController CR limits, the MTC console displays a warning message when you save the migration plan.

Enabling persistent volume resizing for direct volume migration

You can enable persistent volume (PV) resizing for direct volume migration to avoid running out of disk space on the destination cluster.

When the disk usage of a PV reaches a configured level, the MigrationController custom resource (CR) compares the requested storage capacity of a persistent volume claim (PVC) to its actual provisioned capacity. Then, it calculates the space required on the destination cluster.

A pv_resizing_threshold parameter determines when PV resizing is used. The default threshold is 3%. This means that PV resizing occurs when the disk usage of a PV is more than 97%. You can increase this threshold so that PV resizing occurs at a lower disk usage level.

PVC capacity is calculated according to the following criteria:

• If the requested storage capacity (spec.resources.requests.storage) of the PVC is not equal to its actual provisioned capacity (status.capacity.storage), the greater value is used.

• If a PV is provisioned through a PVC and then subsequently changed so that its PV and PVC capacities no longer match, the greater value is used.

Prerequisites

• The PVCs must be attached to one or more running pods so that the MigrationController CR can execute commands.

Procedure

1. Log in to the host cluster.

2. Enable PV resizing by patching the MigrationController CR:

   $ oc patch migrationcontroller migration-controller -p '{"spec":{"enable_dvm_pv_resizing":true}}' \ (1)
     --type='merge' -n openshift-migration

   1	Set the value to false to disable PV resizing.

3. Optional: Update the pv_resizing_threshold parameter to increase the threshold:

   $ oc patch migrationcontroller migration-controller -p '{"spec":{"pv_resizing_threshold":41}}' \ (1)
     --type='merge' -n openshift-migration

   1	The default value is 3.

   When the threshold is exceeded, the following status message is displayed in the MigPlan CR status:

   status:
     conditions:
   ...
     - category: Warn
       durable: true
       lastTransitionTime: "2021-06-17T08:57:01Z"
       message: 'Capacity of the following volumes will be automatically adjusted to avoid disk capacity issues in the target cluster:  [pvc-b800eb7b-cf3b-11eb-a3f7-0eae3e0555f3]'
       reason: Done
       status: "False"
       type: PvCapacityAdjustmentRequired

   For AWS gp2 storage, this message does not appear unless the pv_resizing_threshold is 42% or greater because of the way gp2 calculates volume usage and size. (BZ#1973148)

Enabling cached Kubernetes clients

You can enable cached Kubernetes clients in the MigrationController custom resource (CR) for improved performance during migration. The greatest performance benefit is displayed when migrating between clusters in different regions or with significant network latency.

Cached clients require extra memory because the MigrationController CR caches all API resources that are required for interacting with MigCluster CRs. Requests that are normally sent to the API server are directed to the cache instead. The cache watches the API server for updates.

You can increase the memory limits and requests of the MigrationController CR if OOMKilled errors occur after you enable cached clients.

Procedure

1. Enable cached clients by running the following command:

   $ oc -n openshift-migration patch migrationcontroller migration-controller --type=json --patch \
     '[{ "op": "replace", "path": "/spec/mig_controller_enable_cache", "value": true}]'

2. Optional: Increase the MigrationController CR memory limits by running the following command:

   $ oc -n openshift-migration patch migrationcontroller migration-controller --type=json --patch \
     '[{ "op": "replace", "path": "/spec/mig_controller_limits_memory", "value": <10Gi>}]'

3. Optional: Increase the MigrationController CR memory requests by running the following command:

   $ oc -n openshift-migration patch migrationcontroller migration-controller --type=json --patch \
     '[{ "op": "replace", "path": "/spec/mig_controller_requests_memory", "value": <350Mi>}]'