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Terminology

Table 1. MTC terminology
Term Definition

Source cluster

Cluster from which the applications are migrated.

Destination cluster[1]

Cluster to which the applications are migrated.

Replication repository

Object storage used for copying images, volumes, and Kubernetes objects during indirect migration or for Kubernetes objects during direct volume migration or direct image migration.

The replication repository must be accessible to all clusters.

Host cluster

Cluster on which the migration-controller pod and the web console are running. The host cluster is usually the destination cluster but this is not required.

The host cluster does not require an exposed registry route for direct image migration.

Remote cluster

A remote cluster is usually the source cluster but this is not required.

A remote cluster requires a Secret custom resource that contains the migration-controller service account token.

A remote cluster requires an exposed secure registry route for direct image migration.

Indirect migration

Images, volumes, and Kubernetes objects are copied from the source cluster to the replication repository and then from the replication repository to the destination cluster.

Direct volume migration

Persistent volumes are copied directly from the source cluster to the destination cluster.

Direct image migration

Images are copied directly from the source cluster to the destination cluster.

Stage migration

Data is copied to the destination cluster without stopping the application.

Running a stage migration multiple times reduces the duration of the cutover migration.

Cutover migration

The application is stopped on the source cluster and its resources are migrated to the destination cluster.

State migration

Application state is migrated by copying specific persistent volume claims to the destination cluster.

Rollback migration

Rollback migration rolls back a completed migration.

1 Called the target cluster in 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.

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 OpenShift Container Platform 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 OpenShift Container Platform 4 registry is exposed by default.

Procedure
  • To create a route to an OpenShift Container Platform 4 registry, run the following command:

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

Proxy configuration

For OpenShift Container Platform 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 OpenShift Container Platform 4.2 to 4.11, 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.

Direct volume migration

Direct Volume Migration (DVM) was introduced in MTC 1.4.2. 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.

If you want to perform a DVM from a source cluster behind a proxy, you must configure a TCP proxy that works at the transport layer and forwards the SSL connections transparently without decrypting and re-encrypting them with their own SSL certificates. A Stunnel proxy is an example of such a proxy.

TCP proxy setup for DVM

You can set up a direct connection between the source and the target cluster through a TCP proxy and configure the stunnel_tcp_proxy variable in the MigrationController CR to use the proxy:

apiVersion: migration.openshift.io/v1alpha1
kind: MigrationController
metadata:
  name: migration-controller
  namespace: openshift-migration
spec:
  [...]
  stunnel_tcp_proxy: http://username:password@ip:port

Direct volume migration (DVM) supports only basic authentication for the proxy. Moreover, DVM works only from behind proxies that can tunnel a TCP connection transparently. HTTP/HTTPS proxies in man-in-the-middle mode do not work. The existing cluster-wide proxies might not support this behavior. As a result, the proxy settings for DVM are intentionally kept different from the usual proxy configuration in MTC.

Why use a TCP proxy instead of an HTTP/HTTPS proxy?

You can enable DVM by running Rsync between the source and the target cluster over an OpenShift route. Traffic is encrypted using Stunnel, a TCP proxy. The Stunnel running on the source cluster initiates a TLS connection with the target Stunnel and transfers data over an encrypted channel.

Cluster-wide HTTP/HTTPS proxies in OpenShift are usually configured in man-in-the-middle mode where they negotiate their own TLS session with the outside servers. However, this does not work with Stunnel. Stunnel requires that its TLS session be untouched by the proxy, essentially making the proxy a transparent tunnel which simply forwards the TCP connection as-is. Therefore, you must use a TCP proxy.

Known issue
Migration fails with error Upgrade request required

The migration Controller uses the SPDY protocol to execute commands within remote pods. If the remote cluster is behind a proxy or a firewall that does not support the SPDY protocol, the migration controller fails to execute remote commands. The migration fails with the error message Upgrade request required. Workaround: Use a proxy that supports the SPDY protocol.

In addition to supporting the SPDY protocol, the proxy or firewall also must pass the Upgrade HTTP header to the API server. The client uses this header to open a websocket connection with the API server. If the Upgrade header is blocked by the proxy or firewall, the migration fails with the error message Upgrade request required. Workaround: Ensure that the proxy forwards the Upgrade header.

Tuning network policies for migrations

OpenShift supports restricting traffic to or from pods using NetworkPolicy or EgressFirewalls based on the network plugin used by the cluster. If any of the source namespaces involved in a migration use such mechanisms to restrict network traffic to pods, the restrictions might inadvertently stop traffic to Rsync pods during migration.

Rsync pods running on both the source and the target clusters must connect to each other over an OpenShift Route. Existing NetworkPolicy or EgressNetworkPolicy objects can be configured to automatically exempt Rsync pods from these traffic restrictions.

NetworkPolicy configuration
Egress traffic from Rsync pods

You can use the unique labels of Rsync pods to allow egress traffic to pass from them if the NetworkPolicy configuration in the source or destination namespaces blocks this type of traffic. The following policy allows all egress traffic from Rsync pods in the namespace:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-all-egress-from-rsync-pods
spec:
  podSelector:
    matchLabels:
      owner: directvolumemigration
      app: directvolumemigration-rsync-transfer
  egress:
  - {}
  policyTypes:
  - Egress
Ingress traffic to Rsync pods
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-all-egress-from-rsync-pods
spec:
  podSelector:
    matchLabels:
      owner: directvolumemigration
      app: directvolumemigration-rsync-transfer
  ingress:
  - {}
  policyTypes:
  - Ingress
EgressNetworkPolicy configuration

The EgressNetworkPolicy object or Egress Firewalls are OpenShift constructs designed to block egress traffic leaving the cluster.

Unlike the NetworkPolicy object, the Egress Firewall works at a project level because it applies to all pods in the namespace. Therefore, the unique labels of Rsync pods do not exempt only Rsync pods from the restrictions. However, you can add the CIDR ranges of the source or target cluster to the Allow rule of the policy so that a direct connection can be setup between two clusters.

Based on which cluster the Egress Firewall is present in, you can add the CIDR range of the other cluster to allow egress traffic between the two:

apiVersion: network.openshift.io/v1
kind: EgressNetworkPolicy
metadata:
  name: test-egress-policy
  namespace: <namespace>
spec:
  egress:
  - to:
      cidrSelector: <cidr_of_source_or_target_cluster>
    type: Deny
Configuring supplemental groups for Rsync pods

When your PVCs use a shared storage, you can configure the access to that storage by adding supplemental groups to Rsync pod definitions in order for the pods to allow access:

Table 2. Supplementary groups for Rsync pods
Variable Type Default Description

src_supplemental_groups

string

Not set

Comma-separated list of supplemental groups for source Rsync pods

target_supplemental_groups

string

Not set

Comma-separated list of supplemental groups for target Rsync pods

Example usage

The MigrationController CR can be updated to set values for these supplemental groups:

spec:
  src_supplemental_groups: "1000,2000"
  target_supplemental_groups: "2000,3000"

Configuring proxies

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)
      noProxy: example.com (2)
    1 Stunnel proxy URL for direct volume migration.
    2 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 Specif