Container Service for Kubernetes:Access Services across clusters by using domain names

Prerequisites

• The Fleet management feature is enabled. For more information, see Enable multi-cluster management.

• Two clusters are associated with a Fleet instance. One cluster serves as the Service provider. The other cluster serves as the Service consumer. For more information, see Manage associated clusters.

• The Kubernetes versions of the associated clusters must be 1.22 or later.

• Pods in the Service provider cluster and pods in the Service consumer cluster can communicate with each other. For more information, see MCS overview.

  Note

  After enabling pod CIDR connectivity between clusters, ensure that the security groups for the cluster's node pools have allowed traffic from the pod CIDR blocks of the interconnected clusters.

• The kubeconfig files of the Service provider cluster, Service consumer cluster, and the Fleet instance are obtained, and kubectl is used to connect to the clusters and the instance. For more information, see Obtain the kubeconfig file of a cluster and use kubectl to connect to the cluster.

MCS architecture

To allow a Service in the Service provider cluster to be accessed by a client pod in the Service consumer cluster, perform the following steps:

1. Create a Service named service1 and an application pod that is exposed by using the service1 Service in the Service provider cluster. Create a Service named service1 in the Service consumer cluster.

2. Create a multi-cluster Service named service1 on the Fleet instance. When you create the multi-cluster Service, set the Service name to service1 and the namespace to the namespace of the service1 Service in the Service provider cluster. In addition, specify the names of the Service provider cluster and the Service consumer cluster in the configurations of the multi-cluster Service.

3. Create a client pod in the Service consumer cluster. This way, you can use the client pod to access the backend pods of the service1 Service in the Service provider cluster by using a domain name.

Step 1: Create a Service named service1 in the Service provider cluster

1. Connect to the Service provider cluster by using its kubeconfig file. Then, use the following code block to create a file named web-demo-svc-provider.yaml:

   apiVersion: v1
   kind: Service
   metadata:
     name: service1
     namespace: provider-ns
   spec:
     ports:
     - port: 80
       protocol: TCP
       targetPort: 8080
     selector:
       app: web-demo
     sessionAffinity: None
     type: ClusterIP
   ---
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: web-demo
     namespace: provider-ns
   spec:
     replicas: 1
     selector:
       matchLabels:
         app: web-demo
     template:
       metadata:
         creationTimestamp: null
         labels:
           app: web-demo
       spec:
         containers:
         - env:
           - name: ENV_NAME
             value: cluster-provider
           image: registry-cn-hangzhou.ack.aliyuncs.com/acs/web-demo:0.5.0
           imagePullPolicy: Always
           name: web-demo
         dnsPolicy: ClusterFirst
         restartPolicy: Always
         schedulerName: default-scheduler

2. Run the following command to create a Service named service1 and an application pod that is exposed by using the Service:

   kubectl apply -f web-demo-svc-provider.yaml

Step 2: Create a Service named service1 in the Service consumer cluster

1. Connect to the Service consumer cluster by using its kubeconfig file. Then, use the following code block to create a file named web-demo-svc-consumer.yaml:

   Note

   In this step, you do not need to create application pods.

   apiVersion: v1
   kind: Service
   metadata:
     name: service1
     namespace: provider-ns
   spec:
     ports:
     - port: 80
       protocol: TCP
       targetPort: 8080
     selector:
       app: web-demo
     sessionAffinity: None
     type: ClusterIP

2. Run the following command to create a Service named service1:

   kubectl apply -f web-demo-svc-consumer.yaml

Step 3: Create a multi-cluster Service on the Fleet instance

1. Connect to the Fleet instance by using its kubeconfig file. Then, use the following code block to create a file named multiclusterservice.yaml:

   Note

   • Replace <your consumer cluster id> and <your provider cluster id> with the actual cluster IDs.

   • The name and namespace of the multi-cluster Service must be the same as the name and namespace of the service1 Service in the Service provider cluster.

   apiVersion: networking.one.alibabacloud.com/v1alpha1
   kind: MultiClusterService
   metadata:
      name: service1
      namespace: provider-ns
   spec:
     consumerClusters:
       - name: <your consumer cluster id>
     providerClusters:
       - name: <your provider cluster id>

2. Run the following command to create a multi-cluster Service named service1 on the Fleet instance:

   kubectl apply -f multiclusterservice.yaml

Step 4: Create a client pod in the Service consumer cluster to access the service1 Service in the Service provider cluster

1. Connect to the Service consumer cluster by using its kubeconfig file. Then, use the following code block to create a file named client-pod.yaml:

   apiVersion: v1
   kind: Pod
   metadata:
     name: curl-client
     namespace: customer-ns
   spec:
     containers:
     - name: curl-client
       image: registry-cn-hangzhou.ack.aliyuncs.com/dev/curl:8.11.1
       command: ["sh", "-c", "sleep 12000"]

2. Run the following command to deploy a client pod in the Service consumer cluster:

   kubectl apply -f client-pod.yaml

3. Run the following command to log on to the client pod in the Service consumer cluster and access the service1 Service in the Service provider cluster:

   kubectl exec -it -ncustomer-ns curl-client -- sh
   
   curl service1.provider-ns

   Expected output:

   This is cluster-provider!