karmada/docs/userguide/resource-propagating.md

Resource Propagating

The PropagationPolicy and ClusterPropagationPolicy APIs are provided to propagate resources. For the differences between the two APIs, please see here.

Here, we use PropagationPolicy as an example to describe how to propagate resources.

Before you start

Install Karmada and prepare the karmadactl command-line tool.

Deploy a simplest multi-cluster Deployment

Create a PropagationPolicy object

You can propagate a Deployment by creating a PropagationPolicy object defined in a YAML file. For example, this YAML file describes a Deployment object named nginx under default namespace need to be propagated to member1 cluster:

# propagationpolicy.yaml
apiVersion: policy.karmada.io/v1alpha1
kind: PropagationPolicy
metadata:
  name: example-policy # The default namespace is `default`.
spec:
  resourceSelectors:
    - apiVersion: apps/v1
      kind: Deployment
      name: nginx # If no namespace is specified, the namespace is inherited from the parent object scope.
  placement:
    clusterAffinity:
      clusterNames:
        - member1

1. Create a propagationPolicy base on the YAML file:

kubectl apply -f propagationpolicy.yaml

2. Create a Deployment nginx resource:

kubectl create deployment nginx --image nginx

Note: The resource exists only as a template in karmada. After being propagated to a member cluster, the behavior of the resource is the same as that of a single kubernetes cluster.

Note: Resources and PropagationPolicy are created in no sequence.

3. Display information of the deployment:

karmadactl get deployment

The output is similar to this:

The karmadactl get command now only supports Push mode, [ member3 ] are not push mode

NAME    CLUSTER   READY   UP-TO-DATE   AVAILABLE   AGE   ADOPTION
nginx   member1   1/1     1            1           52s   Y

4. List the pods created by the deployment:

karmadactl get pod -l app=nginx

The output is similar to this:

The karmadactl get command now only supports Push mode, [ member3 ] are not push mode

NAME                     CLUSTER   READY   STATUS    RESTARTS   AGE
nginx-6799fc88d8-s7vv9   member1   1/1     Running   0          52s

Update PropagationPolicy

You can update the propagationPolicy by applying a new YAML file. This YAML file propagates the Deployment to the member2 cluster.

# propagationpolicy-update.yaml
apiVersion: policy.karmada.io/v1alpha1
kind: PropagationPolicy
metadata:
  name: example-policy
spec:
  resourceSelectors:
    - apiVersion: apps/v1
      kind: Deployment
      name: nginx
  placement:
    clusterAffinity:
      clusterNames: # Modify the selected cluster to propagate the Deployment.
        - member2

1. Apply the new YAML file:

kubectl apply -f propagationpolicy-update.yaml

2. Display information of the deployment (the output is similar to this):

The karmadactl get command now only supports Push mode, [ member3 ] are not push mode

NAME    CLUSTER   READY   UP-TO-DATE   AVAILABLE   AGE   ADOPTION
nginx   member2   1/1     1            1           5s    Y

3. List the pods of the deployment (the output is similar to this):

The karmadactl get command now only supports Push mode, [ member3 ] are not push mode

NAME                     CLUSTER   READY   STATUS    RESTARTS   AGE
nginx-6799fc88d8-8t8cc   member2   1/1     Running   0          17s

Note: Updating the .spec.resourceSelectors field to change hit resources is currently not supported.

Update Deployment

You can update the deployment template. The changes will be automatically synchronized to the member clusters.

1. Update deployment replicas to 2
2. Display information of the deployment (the output is similar to this):

The karmadactl get command now only supports Push mode, [ member3 ] are not push mode

NAME    CLUSTER   READY   UP-TO-DATE   AVAILABLE   AGE     ADOPTION
nginx   member2   2/2     2            2           7m59s   Y

3. List the pods of the deployment (the output is similar to this):

The karmadactl get command now only supports Push mode, [ member3 ] are not push mode

NAME                     CLUSTER   READY   STATUS    RESTARTS   AGE
nginx-6799fc88d8-8t8cc   member2   1/1     Running   0          8m12s
nginx-6799fc88d8-zpl4j   member2   1/1     Running   0          17s

Delete a propagationPolicy

Delete the propagationPolicy by name:

kubectl delete propagationpolicy example-policy

Deleting a propagationPolicy does not delete deployments propagated to member clusters. You need to delete deployments in the karmada control-plane:

kubectl delete deployment nginx

Deploy deployment into a specified set of target clusters

Configuring Multi-Cluster HA for Deployment

Multi-Cluster Failover

Please refer to Failover feature of Karmada.

Propagate specified resources to clusters

Adjusting the instance propagation policy of Deployment in clusters