Container Service for Kubernetes:Get started with application distribution

Prerequisites

Ensure that you have:

• Multi-cluster management is enabled.

• Multiple clusters are associated with the Fleet instance.

• kubectl is connected to the Fleet instance using the kubeconfig downloaded from the ACK One console.

• The AliyunAdcpFullAccess policy is granted to your Resource Access Management (RAM) user.

• The AMC command-line tool is installed.

(Optional) Step 1: Create a namespace on the Fleet instance

Create the namespace if it does not exist on the Fleet instance.

Create a namespace named demo:

kubectl create namespace demo

Step 2: Create an application on the Fleet instance

Fleet distributes ConfigMaps, Deployments, and Services. This example uses an NGINX Deployment.

1. Create web-demo.yaml with the following content:

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     namespace: demo
     name: web-demo
   spec:
     replicas: 3
     selector:
       matchLabels:
         app: web-demo
     template:
       metadata:
         labels:
           app: web-demo
       spec:
         containers:
         - name: nginx
           image: registry-cn-hangzhou.ack.aliyuncs.com/acs/web-demo:0.5.0
           ports:
           - containerPort: 80

2. Deploy the application:

   kubectl apply -f web-demo.yaml

Step 3: Create a PropagationPolicy to distribute the application

A PropagationPolicy defines which resources to distribute and to which clusters. Once applied, the controller automatically pushes matching resources to the target clusters.

This example distributes the Deployment to two clusters in Duplicated mode — each cluster runs three replicas independently.

1. Get the member cluster IDs:

   kubectl get mcl

   The output is similar to:

   NAME                                HUB ACCEPTED   MANAGED CLUSTER URLS   JOINED   AVAILABLE   AGE
   cxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx   true                                  True     True        3d23h
   cxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx   true                                  True     True        5d21h

2. Create propagationpolicy.yaml with the following content. Replace ${cluster1-id} and ${cluster2-id} with your cluster IDs.

   ClusterPropagationPolicy distributes cluster-scoped resources (such as Namespaces). PropagationPolicy distributes namespace-scoped resources and selects only within its own namespace.

   apiVersion: policy.one.alibabacloud.com/v1alpha1
   kind: ClusterPropagationPolicy
   metadata:
     name: web-demo
   spec:
     resourceSelectors:
     - apiVersion: v1
       kind: Namespace
       name: demo
     placement:
       clusterAffinity:
         clusterNames:
         - ${cluster1-id} # The ID of your cluster.
         - ${cluster2-id} # The ID of your cluster.
       replicaScheduling:
         replicaSchedulingType: Duplicated
   ---
   apiVersion: policy.one.alibabacloud.com/v1alpha1
   kind: PropagationPolicy
   metadata:
     name: web-demo
     namespace: demo
   spec:
     preserveResourcesOnDeletion: true # When true, deleting resources from the Fleet instance keeps them in the member cluster. Set to false to delete them together.
     resourceSelectors:
     - apiVersion: apps/v1
       kind: Deployment
       name: web-demo
       namespace: demo
     placement:
       clusterAffinity:
         clusterNames:
         - ${cluster1-id} # The ID of your cluster.
         - ${cluster2-id} # The ID of your cluster.
       replicaScheduling:
         replicaSchedulingType: Duplicated

   Key parameters are listed below. The full parameter list is in PropagationPolicy.

   Parameter	Description	Example
   resourceSelectors	Resources to distribute. Match by apiVersion, kind, name, namespace, or labelSelector.	Select the web-demo Deployment in the demo namespace.
   placement.clusterAffinity	Target clusters for distribution. Enter cluster IDs, not cluster names.	${cluster1-id}, ${cluster2-id}
   replicaScheduling.replicaSchedulingType	Scheduling mode. Duplicated replicates the full replica count (defined by spec.replicas) to each cluster.	Duplicated

3. Apply the PropagationPolicy:

   kubectl apply -f propagationpolicy.yaml

(Optional) Step 4: Create an OverridePolicy to customize per-cluster configuration

An OverridePolicy modifies resource configuration before deployment, letting you tailor settings for individual clusters.

This example targets ${cluster2-id} with two changes:

• Reduces replicas from 3 to 1

• Prepends a registry prefix to the image

Before applying the OverridePolicy, the Deployment on ${cluster2-id} has:

spec:
  replicas: 3
  ...
  containers:
    - image: registry-cn-hangzhou.ack.aliyuncs.com/acs/web-demo:0.5.0

After applying the OverridePolicy, the Deployment on ${cluster2-id} becomes:

spec:
  replicas: 1
  ...
  containers:
    - image: {{Registry}}/registry-cn-hangzhou.ack.aliyuncs.com/acs/web-demo:0.5.0

1. Create overridepolicy.yaml with the following content:

   apiVersion: policy.one.alibabacloud.com/v1alpha1
   kind: OverridePolicy
   metadata:
     name: example
     namespace: demo
   spec:
     resourceSelectors:
       - apiVersion: apps/v1
         kind: Deployment
         name: web-demo
     overrideRules:
       - targetCluster:
           clusterNames:
             - ${cluster2-id}
         overriders:
           plaintext:
             - operator: replace
               path: /spec/replicas
               value: 1
           imageOverrider:
             - component: Registry
               operator: add
               value: {{Registry}}

   Key parameters are listed below. The full parameter list is in OverridePolicy.

   Parameter	Description	Example
   resourceSelectors	Resources to override. Match by apiVersion, kind, name, namespace, or labelSelector.	Select the web-demo Deployment.
   overrideRules.plaintext	Override resource fields with JSONPatch. Set operator, path, and value.	Change spec.replicas to 1.
   overrideRules.imageOverrider	Override image components: Registry, Repository, or Version.	Prepend a registry prefix to the image.

2. Apply the OverridePolicy:

   kubectl apply -f overridepolicy.yaml

Step 5: View the distribution status

Check whether the application has been distributed to all member clusters:

kubectl amc get deploy -ndemo -M

The output is similar to:

NAME       CLUSTER          READY   UP-TO-DATE   AVAILABLE   AGE    ADOPTION
web-demo   cxxxxxxxxxxxxx   3/3     3            3           3d4h   Y
web-demo   cxxxxxxxxxxxxx   3/3     3            3           3d4h   Y

READY: 3/3 and ADOPTION: Y confirm the application runs in each cluster.

Step 6: Update the application

1. Update web-demo.yaml to increase replicas to 4:

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     namespace: demo
     name: web-demo
   spec:
     replicas: 4
     selector:
       matchLabels:
         app: web-demo
     template:
       metadata:
         labels:
           app: web-demo
       spec:
         containers:
         - name: nginx
           image: registry-cn-hangzhou.ack.aliyuncs.com/acs/web-demo:0.5.0
           ports:
           - containerPort: 80

2. Apply the updated manifest:

   kubectl apply -f web-demo.yaml

3. Verify propagation to all clusters:

   kubectl amc get deploy -ndemo -M

   The output is similar to:

   NAME       CLUSTER          READY   UP-TO-DATE   AVAILABLE   AGE    ADOPTION
   web-demo   cxxxxxxxxxxxxx   4/4     4            4           3d4h   Y
   web-demo   cxxxxxxxxxxxxx   4/4     4            4           3d4h   Y

   READY: 4/4 confirms both clusters are updated.

Step 7: Delete application resources

By default, removing an application or PropagationPolicy from the Fleet instance does not delete resources from member clusters.

To delete resources from member clusters:

1. Set preserveResourcesOnDeletion to false in ClusterPropagationPolicy:

   apiVersion: policy.one.alibabacloud.com/v1alpha1
   kind: ClusterPropagationPolicy
   metadata:
     name: web-demo
   spec:
     preserveResourcesOnDeletion: false
     resourceSelectors:
     - apiVersion: apps/v1
       kind: Deployment
       name: web-demo
     - apiVersion: v1
       kind: Namespace
       name: demo
     placement:
       clusterAffinity:
         clusterNames:
         - ${cluster1-id} # The ID of your cluster.
         - ${cluster2-id} # The ID of your cluster.
       replicaScheduling:
         replicaSchedulingType: Duplicated

2. Apply the updated policy:

   kubectl apply -f propagationpolicy.yaml

3. Delete the application resources:

   kubectl delete -f web-demo.yaml

4. Confirm removal from member clusters:

   kubectl amc get deploy -ndemo -M

   The output is similar to:

   cluster(cxxxxxxxxxxxxx): deployments.apps "web-demo" not found
   cluster(cxxxxxxxxxxxxx): deployments.apps "web-demo" not found

References

• Monitor distributed applications: Monitoring management

• Implement zone-disaster recovery: Use MSE multi-cluster gateways to implement zone-disaster recovery in ACK One

• Full parameter reference: PropagationPolicy and OverridePolicy