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Migrate Kubernetes Objects Using Storage Version Migration

FEATURE STATE:Kubernetes v1.30 [alpha] (enabled by default: false)

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 at or later than version v1.30.

To check the version, enter kubectl version.

Ensure that your cluster has the StorageVersionMigrator and InformerResourceVersionfeature 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:EncryptionConfigurationapiVersion:apiserver.config.k8s.io/v1resources:- resources:- secretsproviders:- aescbc:keys:- name:key1secret: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:EncryptionConfigurationapiVersion:apiserver.config.k8s.io/v1resources:- resources:- secretsproviders:- aescbc:keys:- name:key2secret:c2VjcmV0IGlzIHNlY3VyZSwgaXMgaXQ/- aescbc:keys:- name:key1secret: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:StorageVersionMigrationapiVersion:storagemigration.k8s.io/v1alpha1metadata:name:secrets-migrationspec:resource:group:""version:v1resource: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:StorageVersionMigrationapiVersion:storagemigration.k8s.io/v1alpha1metadata:name:secrets-migrationuid:628f6922-a9cb-4514-b076-12d3c178967cresourceVersion:"90"creationTimestamp:"2024-03-12T20:29:45Z"spec:resource:group:""version:v1resource:secretsstatus:conditions:- type:Runningstatus:"False"lastUpdateTime:"2024-03-12T20:29:46Z"reason:StorageVersionMigrationInProgress- type:Succeededstatus:"True"lastUpdateTime:"2024-03-12T20:29:46Z"reason:StorageVersionMigrationSucceededresourceVersion:"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/v1kind:CustomResourceDefinitionmetadata:name:selfierequests.stable.example.comspec:group:stable.example.comnames:plural:SelfieRequestssingular:SelfieRequestkind:SelfieRequestlistKind:SelfieRequestListscope:Namespacedversions:- name:v1served:truestorage:trueschema:openAPIV3Schema:type:objectproperties:hostPort:type:stringconversion:strategy:Webhookwebhook: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/v1kind:SelfieRequestmetadata:name:cr1namespace: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/v1kind:CustomResourceDefinitionmetadata:name:selfierequests.stable.example.comspec:group:stable.example.comnames:plural:SelfieRequestssingular:SelfieRequestkind:SelfieRequestlistKind:SelfieRequestListscope:Namespacedversions:- name:v2served:truestorage:trueschema:openAPIV3Schema:type:objectproperties:host:type:stringport:type:string- name:v1served:truestorage:falseschema:openAPIV3Schema:type:objectproperties:hostPort:type:stringconversion:strategy:Webhookwebhook: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/v2kind:SelfieRequestmetadata:name:cr2namespace: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:StorageVersionMigrationapiVersion:storagemigration.k8s.io/v1alpha1metadata:name:crdsvmspec:resource:group:stable.example.comversion:v1resource:SelfieRequest