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Version: v1.12

Resource Migration and Rollback

Objectives​

Assuming you have a single kubernetes cluster which already has many native resource installed, furthermore, you want to migrate the existing resource to Karmada and then achieve multi-cluster management.

So, this section will guide you to cover:

  • Migrate application from Kubernetes to Karmada.
  • Rollback application migration.

Prerequisites​

Karmada with multi cluster has been installed​

Step 1: Run the command​

git clone https://github.com/karmada-io/karmada
cd karmada
hack/local-up-karmada.sh
export KUBECONFIG=~/.kube/karmada.config:~/.kube/members.config

Note:

Before guide started, we should install at least three kubernetes clusters, one is for Karmada control plane, the other two for member clusters. For convenience, we use hack/local-up-karmada.sh script to quickly prepare the above clusters.

After the above command executed, you will see Karmada control plane installed with multi member clusters.

Preset resource in a member cluster​

To simulate resources already exist in member cluster, we deploy simple Deployment to member1 cluster.

Step 2: Write the code​

Create new file /tmp/deployments.yaml and copy text below to it:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deploy
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 2
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
        - name: nginx
          image: nginx:latest
          ports:
            - containerPort: 80

Step 3: Run the command​

$ kubectl --context member1 apply -f /tmp/deployments.yaml
deployment.apps/nginx-deploy created

$ karmadactl --karmada-context karmada-apiserver get deploy --operation-scope=all
NAME           CLUSTER   READY   UP-TO-DATE   AVAILABLE   AGE   ADOPTION
nginx-deploy   member1   2/2     2            2           15m   N

You will see the current nginx-deploy deployment in the member1 cluster, with ADOPTION=N indicating it is not currently managed by Karmada.

Tutorials​

Migrate application to Karmada​

To make the tutorial simpler and easier to understand, here we assume the application example contains only a single simple deployment.

Step 1: Run the command​

$ kubectl --context karmada-apiserver apply -f /tmp/deployments.yaml
deployment.apps/nginx-deploy created

$ karmadactl --karmada-context karmada-apiserver get deploy --operation-scope=all
NAME           CLUSTER   READY   UP-TO-DATE   AVAILABLE   AGE   ADOPTION
nginx-deploy   Karmada   0/2     0            0           7s    -
nginx-deploy   member1   2/2     2            2           16m   N

You will see that the Deployment has been deployed to the Karmada control plane as a ResourceTemplate, but there is currently no matching PropagationPolicy to propagate it.

Step 2: Write the code​

Create new file /tmp/pp-for-migrating-deployments.yaml and copy text below to it:

apiVersion: policy.karmada.io/v1alpha1
kind: PropagationPolicy
metadata:
  name: migrate-pp
spec:
  conflictResolution: Overwrite
  placement:
    clusterAffinity:
      clusterNames:
      - member1
  resourceSelectors:
  - apiVersion: apps/v1
    kind: Deployment
    name: nginx-deploy

Note:

You should pay attention to two fields：

  • spec.conflictResolution: Overwrite：the value must be Overwrite.
  • spec.resourceSelectors：selecting resources to migrate, you can define your custom ResourceSelector.

Step 3: Run the Command​

Apply the above PropagationPolicy to the Karmada control plane:

$ kubectl --context karmada-apiserver apply -f /tmp/pp-for-migrating-deployments.yaml
propagationpolicy.policy.karmada.io/migrate-pp created

Step 4: Verification​

$ karmadactl --karmada-context karmada-apiserver get deploy --operation-scope=all
NAME           CLUSTER   READY   UP-TO-DATE   AVAILABLE   AGE   ADOPTION
nginx-deploy   Karmada   2/2     2            2           34s   -
nginx-deploy   member1   2/2     2            2           16m   Y

$ karmadactl --karmada-context karmada-apiserver get pods --operation-scope=all
NAME                            CLUSTER   READY   STATUS    RESTARTS   AGE
nginx-deploy-54b9c68f67-4qjrz   member1   1/1     Running   0          16m
nginx-deploy-54b9c68f67-f4qpm   member1   1/1     Running   0          16m

You will see that all Deployments are ready, which means nginx-deploy in the member1 cluster is successfully taken over by Karmada:

  • AGE=16m indicates the resource is taken over rather than recreated, with corresponding pods no need to be restarted.
  • ADOPTION=Y indicates that the resource is now managed by Karmada.

You have now completed the migration.

Rollback Migration​

Step 5: Set preserveResourcesOnDeletion for PropagationPolicy​

Run the following command to modify PropagationPolicy/migrate-pp, setting spec.preserveResourcesOnDeletion=true:

$ kubectl --context karmada-apiserver patch pp migrate-pp --type='json' -p '[{"op": "replace", "path": "/spec/preserveResourcesOnDeletion", "value": true}]'
propagationpolicy.policy.karmada.io/nginx-pp patched

Step 6: Delete the Resource Template from the Control Plane​

Run the following command:

$ kubectl --context karmada-apiserver delete -f /tmp/deployments.yaml
deployment.apps "nginx-deploy" deleted

Step 7: Verification​

Run the following command:

$ karmadactl --karmada-context karmada-apiserver get deploy --operation-scope=all
NAME           CLUSTER   READY   UP-TO-DATE   AVAILABLE   AGE   ADOPTION
nginx-deploy   member1   2/2     2            2           17m   N
...

You will see that the resource template in the control plane has been deleted, and the resources in the member clusters remain intact, with ADOPTION=N indicating that the resource is not managed by Karmada.

You have now completed the migration rollback.