Migrate Kubernetes Objects Using Storage Version Migration

Kubernetes relies on API data being actively re-written, to support some maintenance activities related to at rest storage. Two prominent examples are the versioned schema of stored resources (that is, the preferred storage schema changing from v1 to v2 for a given resource) and encryption at rest (that is, rewriting stale data based on a change in how the data should be encrypted).

Before you begin

Install kubectl.

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

• Killercoda
• Play with Kubernetes

Your Kubernetes server must be at or later than version v1.30. To check the version, enter kubectl version.

Ensure that your cluster has the StorageVersionMigrator and InformerResourceVersion feature gates enabled. You will need control plane administrator access to make that change.

Enable storage version migration REST api by setting runtime config storagemigration.k8s.io/v1alpha1 to true for the API server. For more information on how to do that, read enable or disable a Kubernetes API.

Re-encrypt Kubernetes secrets using storage version migration

• To begin with, configure KMS provider to encrypt data at rest in etcd using following encryption configuration.

  kind: EncryptionConfiguration
  apiVersion: apiserver.config.k8s.io/v1
  resources:
  - resources:
    - secrets
    providers:
    - aescbc:
        keys:
        - name: key1
          secret: c2VjcmV0IGlzIHNlY3VyZQ==
  

  Make sure to enable automatic reload of encryption configuration file by setting --encryption-provider-config-automatic-reload to true.

• Create a Secret using kubectl.

  kubectl create secret generic my-secret --from-literal=key1=supersecret
  

• Verify the serialized data for that Secret object is prefixed with k8s:enc:aescbc:v1:key1.

• Update the encryption configuration file as follows to rotate the encryption key.

  kind: EncryptionConfiguration
  apiVersion: apiserver.config.k8s.io/v1
  resources:
  - resources:
    - secrets
    providers:
    - aescbc:
        keys:
        - name: key2
          secret: c2VjcmV0IGlzIHNlY3VyZSwgaXMgaXQ/
    - aescbc:
        keys:
        - name: key1
          secret: c2VjcmV0IGlzIHNlY3VyZQ==
  

• To ensure that previously created secret my-secret is re-encrypted with new key key2, you will use Storage Version Migration.

• Create a StorageVersionMigration manifest named migrate-secret.yaml as follows:

  kind: StorageVersionMigration
  apiVersion: storagemigration.k8s.io/v1alpha1
  metadata:
    name: secrets-migration
  spec:
    resource:
      group: ""
      version: v1
      resource: secrets
  

  Create the object using kubectl as follows:

  kubectl apply -f migrate-secret.yaml
  

• Monitor migration of Secrets by checking the .status of the StorageVersionMigration. A successful migration should have its Succeeded condition set to true. Get the StorageVersionMigration object as follows:

  kubectl get storageversionmigration.storagemigration.k8s.io/secrets-migration -o yaml
  

  The output is similar to:

  kind: StorageVersionMigration
  apiVersion: storagemigration.k8s.io/v1alpha1
  metadata:
    name: secrets-migration
    uid: 628f6922-a9cb-4514-b076-12d3c178967c
    resourceVersion: "90"
    creationTimestamp: "2024-03-12T20:29:45Z"
  spec:
    resource:
      group: ""
      version: v1
      resource: secrets
  status:
    conditions:
    - type: Running
      status: "False"
      lastUpdateTime: "2024-03-12T20:29:46Z"
      reason: StorageVersionMigrationInProgress
    - type: Succeeded
      status: "True"
      lastUpdateTime: "2024-03-12T20:29:46Z"
      reason: StorageVersionMigrationSucceeded
    resourceVersion: "84"
  

• Verify the stored secret is now prefixed with k8s:enc:aescbc:v1:key2.

Update the preferred storage schema of a CRD

Consider a scenario where a CustomResourceDefinition (CRD) is created to serve custom resources (CRs) and is set as the preferred storage schema. When it's time to introduce v2 of the CRD, it can be added for serving only with a conversion webhook. This enables a smoother transition where users can create CRs using either the v1 or v2 schema, with the webhook in place to perform the necessary schema conversion between them. Before setting v2 as the preferred storage schema version, it's important to ensure that all existing CRs stored as v1 are migrated to v2. This migration can be achieved through Storage Version Migration to migrate all CRs from v1 to v2.

• Create a manifest for the CRD, named test-crd.yaml, as follows:

  apiVersion: apiextensions.k8s.io/v1
  kind: CustomResourceDefinition
  metadata:
    name: selfierequests.stable.example.com
  spec:
    group: stable.example.com
    names:
      plural: SelfieRequests
      singular: SelfieRequest
      kind: SelfieRequest
      listKind: SelfieRequestList
    scope: Namespaced
    versions:
    - name: v1
      served: true
      storage: true
      schema:
        openAPIV3Schema:
          type: object
          properties:
            hostPort:
              type: string
    conversion:
      strategy: Webhook
      webhook:
        clientConfig:
          url: "https://127.0.0.1:9443/crdconvert"
          caBundle: <CABundle info>
      conversionReviewVersions:
      - v1
      - v2
  

  Create CRD using kubectl:

  kubectl apply -f test-crd.yaml
  

• Create a manifest for an example testcrd. Name the manifest cr1.yaml and use these contents:

  apiVersion: stable.example.com/v1
  kind: SelfieRequest
  metadata:
    name: cr1
    namespace: default
  

  Create CR using kubectl:

  kubectl apply -f cr1.yaml
  

• Verify that CR is written and stored as v1 by getting the object from etcd.

  ETCDCTL_API=3 etcdctl get /kubernetes.io/stable.example.com/testcrds/default/cr1 [...] | hexdump -C
  

  where [...] contains the additional arguments for connecting to the etcd server.

• Update the CRD test-crd.yaml to include v2 version for serving and storage and v1 as serving only, as follows:

  apiVersion: apiextensions.k8s.io/v1
  kind: CustomResourceDefinition
  metadata:
  name: selfierequests.stable.example.com
  spec:
    group: stable.example.com
    names:
      plural: SelfieRequests
      singular: SelfieRequest
      kind: SelfieRequest
      listKind: SelfieRequestList
    scope: Namespaced
    versions:
      - name: v2
        served: true
        storage: true
        schema:
          openAPIV3Schema:
            type: object
            properties:
              host:
                type: string
              port:
                type: string
      - name: v1
        served: true
        storage: false
        schema:
          openAPIV3Schema:
            type: object
            properties:
              hostPort:
                type: string
    conversion:
      strategy: Webhook
      webhook:
        clientConfig:
          url: "https://127.0.0.1:9443/crdconvert"
          caBundle: <CABundle info>
        conversionReviewVersions:
          - v1
          - v2
  

  Update CRD using kubectl:

  kubectl apply -f test-crd.yaml
  

• Create CR resource file with name cr2.yaml as follows:

  apiVersion: stable.example.com/v2
  kind: SelfieRequest
  metadata:
    name: cr2
    namespace: default
  

• Create CR using kubectl:

  kubectl apply -f cr2.yaml
  

• Verify that CR is written and stored as v2 by getting the object from etcd.

  ETCDCTL_API=3 etcdctl get /kubernetes.io/stable.example.com/testcrds/default/cr2 [...] | hexdump -C
  

  where [...] contains the additional arguments for connecting to the etcd server.

• Create a StorageVersionMigration manifest named migrate-crd.yaml, with the contents as follows:

  kind: StorageVersionMigration
  apiVersion: storagemigration.k8s.io/v1alpha1
  metadata:
    name: crdsvm
  spec:
    resource:
      group: stable.example.com
      version: v1
      resource: SelfieRequest
  

  Create the object using kubectl as follows:

  kubectl apply -f migrate-crd.yaml
  

• Monitor migration of secrets using status. Successful migration should have Succeeded condition set to "True" in the status field. Get the migration resource as follows:

  kubectl get storageversionmigration.storagemigration.k8s.io/crdsvm -o yaml
  

  The output is similar to:

  kind: StorageVersionMigration
  apiVersion: storagemigration.k8s.io/v1alpha1
  metadata:
    name: crdsvm
    uid: 13062fe4-32d7-47cc-9528-5067fa0c6ac8
    resourceVersion: "111"
    creationTimestamp: "2024-03-12T22:40:01Z"
  spec:
    resource:
      group: stable.example.com
      version: v1
      resource: testcrds
  status:
    conditions:
      - type: Running
        status: "False"
        lastUpdateTime: "2024-03-12T22:40:03Z"
        reason: StorageVersionMigrationInProgress
      - type: Succeeded
        status: "True"
        lastUpdateTime: "2024-03-12T22:40:03Z"
        reason: StorageVersionMigrationSucceeded
    resourceVersion: "106"
  

• Verify that previously created cr1 is now written and stored as v2 by getting the object from etcd.

  ETCDCTL_API=3 etcdctl get /kubernetes.io/stable.example.com/testcrds/default/cr1 [...] | hexdump -C
  

  where [...] contains the additional arguments for connecting to the etcd server.