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.

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.

Last modified April 04, 2024 at 12:22 PM PST: docs: KEP-4192 PR feedback - feature gates don't match the code (2a0b55d3c7)

Migrate Kubernetes Objects Using Storage Version Migration

Before you begin

Re-encrypt Kubernetes secrets using storage version migration

Update the preferred storage schema of a CRD

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