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Migrate Kubernetes Objects Using Storage Version Migration

FEATURE STATE: Kubernetes v1.30 [alpha]

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:

Your Kubernetes server must be 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-secert 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.