Container Service for Kubernetes:Use headless multi-cluster Services to access specified pods of StatefulSets across clusters

How it works

A headless Service has no ClusterIP (clusterIP: None). Instead of resolving to a single Service IP, its DNS record resolves directly to the IP addresses of all matching pods. When you export a headless Service with a ServiceExport and import it with a ServiceImport of type Headless, ACK One extends this resolution across clusters.

In this example:

• ACK Cluster 1 is the service provider. It runs a MySQL StatefulSet and a ServiceExport that makes the mysql Service available to other clusters.

• ACK Cluster 2 is the service consumer. It has a ServiceImport that maps to the exported mysql Service, plus a client pod that connects to specific MySQL pods by domain name.

Prerequisites

Before you begin, ensure that you have:

Fleet-level requirements:

• Fleet management enabled

• ACK Cluster 1 and ACK Cluster 2 both associated with the Fleet instance

Cluster-level requirements:

• Kubernetes 1.22 or later on both clusters

• kubeconfig files obtained and kubectl connected to each cluster. For details, see Get a cluster kubeconfig and connect to the cluster using kubectl

• Network connectivity between the two clusters:

  • Same Virtual Private Cloud (VPC): no additional configuration needed

  • Different VPCs: inter-VPC communication enabled via Cloud Enterprise Network (CEN). For setup instructions, see Create a VPC connection

Step 1: Deploy a MySQL StatefulSet and create a ServiceExport in ACK Cluster 1

1. Create the provider-ns namespace:

   kubectl create ns provider-ns

2. Create a file named mysql.yaml with the following content:

   apiVersion: v1
   kind: Secret
   metadata:
       name: mysecret
   type: Opaque
   data:
      ROOT_PASSWORD: cGFzc3dvcmQ=
   ---
   apiVersion: v1
   kind: Service
   metadata:
     name: mysql
     labels:
       app: mysql
   spec:
     clusterIP: None
     selector:
       app: mysql
     ports:
       - name: tcp
         protocol: TCP
         port: 3306
   ---
   apiVersion: apps/v1
   kind: StatefulSet
   metadata:
     name: mysql
   spec:
     replicas: 2  # Two replicated pods are provisioned for the MySQL database.
     serviceName: mysql
     selector:
       matchLabels:
         app: mysql
     template:
       metadata:
         labels:
           app: mysql
       spec:
         terminationGracePeriodSeconds: 10
         containers:
           - name: mysql
             image: mysql:5.6
             ports:
               - name: tcp
                 protocol: TCP
                 containerPort: 3306
             env:
               - name: MYSQL_ROOT_PASSWORD
                 valueFrom:
                  secretKeyRef:
                   key: ROOT_PASSWORD
                   name: mysecret
             volumeMounts:
               - name: data
                 mountPath: /var/lib/mysql
     volumeClaimTemplates:
       - metadata:
           name: data
         spec:
           storageClassName: standard
           accessModes:
             - ReadWriteOnce
           resources:
             requests:
               storage: 50Gi
           storageClassName: alicloud-disk-topology-alltype

3. Deploy the MySQL StatefulSet:

   kubectl -n provider-ns create -f mysql.yaml

   Expected output:

   secret/mysecret created
   service/mysql created
   statefulset.apps/mysql created

4. Create a file named serviceexport.yaml with the following content:

   apiVersion: multicluster.x-k8s.io/v1alpha1
   kind: ServiceExport
   metadata:
     name: mysql           # Specify the name of the Service to export.

5. Create the ServiceExport:

   kubectl -n provider-ns create -f serviceexport.yaml

   Expected output:

   serviceexport.multicluster.x-k8s.io/mysql created

Step 2: Create a ServiceImport in ACK Cluster 2

1. Create the provider-ns namespace in ACK Cluster 2:

   kubectl create ns provider-ns

2. Create a file named serviceimport.yaml with the following content:

   Important

   Set type to Headless. This tells ACK One to resolve the import to individual pod IPs rather than a virtual Service IP.

   apiVersion: multicluster.x-k8s.io/v1alpha1
   kind: ServiceImport
   metadata:
     name: mysql              # Must match the ServiceExport name.
   spec:
     ports:
     - name: tcp
       port: 3306
       protocol: TCP
     type: Headless

3. Create the ServiceImport:

   kubectl -n provider-ns create -f serviceimport.yaml

   Expected output:

   serviceimport.multicluster.x-k8s.io/mysql created

Step 3: Access a specific MySQL pod from ACK Cluster 2

Within a single cluster, a StatefulSet pod is reachable at <pod-name>.<svc-name>.<namespace>.svc.cluster.local. Across clusters, ACK One extends this pattern with two domain name formats:

Method 1 uses the cluster's existing DNS and requires no extra configuration—the amcs- prefix routes cross-cluster pod resolution through the local DNS server. Method 2 uses the clusterset.local domain, which requires the CoreDNS multicluster plugin. Install or update CoreDNS to version 1.9.3 or later and add a plugin entry before using it.

Use Method 1 for simplicity. Use Method 2 when you need the cluster ID embedded in the domain, for example, to target pods in a specific member cluster of the Fleet.

Both methods require a client pod in ACK Cluster 2. Create a file named mysqlclient.yaml:

apiVersion: v1
kind: Pod
metadata:
  name: mysql-client
spec:
  containers:
  - name: mysql-client
    image: mysql:5.6
    command: ["sh", "-c", "sleep 12000"]

Deploy the client pod:

kubectl create -f mysqlclient.yaml

Expected output:

pod/mysql-client created

kubectl exec -it mysql-client -- mysql -h mysql-0.amcs-mysql.provider-ns.svc.cluster.local -P3306 -uroot -ppassword

kubectl exec -it mysql-client -- mysql -h mysql-1.amcs-mysql.provider-ns.svc.cluster.local -P3306 -uroot -ppassword

Warning: Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.6.51 MySQL Community Server (GPL)

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