All Products
Search
Document Center

Container Service for Kubernetes:Use the CLI to configure MCS

Last Updated:Aug 02, 2024

The multi-cluster Services (MCS) feature allows you to access Services across Kubernetes clusters without the need to create load balancers. This topic describes how to create a ServiceExport and ServiceImport on a Fleet instance to configure MCS in order to access Services across Kubernetes clusters.

Prerequisites

Overview

The MCS feature allows you to access Services across Kubernetes clusters. The following figure shows the architecture of the MCS feature.

多集群服务

  1. The administrator deployed application resources, such as namespaces, Deployments, and Services, in a Service provider cluster (ACK Cluster 1) and a Service consumer cluster (ACK Cluster 2). The administrator also created MCS resources, including a ServiceExport and a ServiceImport.

  2. The Fleet instance listens on the ServiceExport and ServiceImport in the associated ACK clusters, and synchronizes the MCS endpoint information.

  3. The client pod in ACK Cluster 2 can access Service 1 in ACK Cluster 1.

Step 1: Create resources for the Service provider

Skip this step if Kubernetes Services and resources are already deployed in ACK Cluster 1 where the Service provider resides.

  1. Run the following command in ACK Cluster 1 to create a namespace for the Service provider.

    In this example, the provider-ns namespace is created.

    kubectl create ns provider-ns
  2. Create a Kubernetes Service and a Deployment for the Service provider in ACK Cluster 1.

    1. Create a file named app-meta.yaml and add the following content to the file:

      apiVersion: v1       # The Service provider. 
      kind: Service
      metadata:
        name: service1
        namespace: provider-ns
      spec:
        ports:
        - name: http
          port: 80
          protocol: TCP
          targetPort: 8080
        selector:
          app: web-demo
        sessionAffinity: None
        type: ClusterIP
      ---
      apiVersion: apps/v1
      kind: Deployment
      metadata:
        labels:
          app: web-demo
        name: web-demo
        namespace: provider-ns
      spec:
        replicas: 2
        selector:
          matchLabels:
            app: web-demo
        template:
          metadata:
            labels:
              app: web-demo
          spec:
            containers:
            - image: acr-multiple-clusters-registry.cn-hangzhou.cr.aliyuncs.com/ack-multiple-clusters/web-demo:0.4.0
              name: web-demo
              env:
              - name: ENV_NAME
                value: cluster1-beijing
    2. Run the following command to create resources in ACK Cluster 1:

      kubectl apply -f app-meta.yaml
    3. Run the following command to create a ServiceExport in ACK Cluster 1 and specify the Service to be exported through a multi-cluster Service:

      apiVersion: multicluster.x-k8s.io/v1alpha1
      kind: ServiceExport
      metadata:
        name: service1           # The value must be the same as the name of the Service that you want to export. 
        namespace: provider-ns   # The value must be the same as the namespace of the Service that you want to export.

      The following table describes the parameters.

      Parameter

      Description

      metadata.name

      The name of the Service that you want to export.

      metadata.namespace

      The namespace of the Service that you want to export.

Step 2: Configure the Service consumer cluster

  1. Run the following command in ACK Cluster 2 to create a namespace for the Service consumer.

    In this example, the provider-ns namespace is created.

    kubectl create ns provider-ns
  2. Create a file and add the following content to the file to create a ServiceImport in ACK Cluster 2:

    apiVersion: multicluster.x-k8s.io/v1alpha1
    kind: ServiceImport
    metadata:
      name: service1           
      namespace: provider-ns   
    spec:
      ports:                   # The values in this field must be the same as the ports used by the Service that you want to export. 
      - name: http
        port: 80
        protocol: TCP
      type: ClusterSetIP

    The spec section of the ServiceImport displays only partial parameters. The following table describes all parameters in the spec section.

    Parameter

    Description

    metadata.name 

    The Service name. The name must be the same as that of the Service you want to export.

    metadata.namespace

    The namespace of the Service. The namespace must be the same as that of the Service you want to export.

    spec. ports. name

    The name of the port. The value must be the same as that of the Service you want to export.

    spec. ports. protocol

    The protocol. The value must be the same as that of the Service you want to export.

    spec. ports. appProtocol

    The application protocol. The value must be the same as that of the Service you want to export.

    spec. ports. port

    The port. The value must be the same as that of the Service you want to export.

    spec. ips

    The virtual IP address of the Service. This parameter is specified by the Fleet instance. You can ignore this parameter.

    spec. type

    Valid values: ClusterSetIP and Headless.

    When the ClusterIP parameter of the Service is set to None, the Service is a headless Service. In this scenario, set type to Headless.

    In other scenarios, set type to ClusterSetIP.

    spec. sessionAffinity

    Session affinity. Valid values: ClientIP and None. The value must be the same as that of the Service you want to export.

    spec. sessionAffinityConfig

    The session affinity configuration. The value must be the same as that of the Service you want to export.

Step 3: Access the Service across clusters

The client pod in ACK Cluster 2 can use one of the following methods to access Service 1 in ACK Cluster 1.

Method 1: Use the name of the Service

After you create a ServiceImport in ACK Cluster 2, the Fleet instance creates a multi-cluster Service prefixed with amcs- in ACK Cluster 2.

The client pod in ACK Cluster 2 can use amcs-service1.provider-ns to access Service 1 in ACK Cluster 1.

  1. Run the following command in ACK Cluster 2 to query the Service information:

    kubectl get service -n provider-ns

    Expected output:

    NAME            TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)   AGE
    amcs-service1   ClusterIP   172.xx.xx.xx   <none>        80/TCP    26m
  2. Run the following command in the client pod in ACK Cluster 2 to access Service 1 in ACK Cluster 1.

    curl amcs-service1.provider-ns

Method 2: Use the domain name of the Service

  1. Install or update CoreDNS in ACK Cluster 2. The version of CoreDNS must be 1.9.3 or later. For more information, see CoreDNS and Manage components.

  2. Modify the Corefile configurations of CoreDNS.

    1. Run the following command to modify the ConfigMap of CoreDNS:

      kubectl edit configmap coredns -n kube-system
    2. In the Corefile field, add multicluster clusterset.local to enable domain name resolution for multi-cluster Services.

      apiVersion: v1
      data:
        Corefile: |
          .:53 {
              errors
              health {
                 lameduck 15s
              }
              ready
              multicluster clusterset.local    # Add this configuration to enable domain name resolution for multi-cluster Services. 
              kubernetes cluster.local in-addr.arpa ip6.arpa {
      
                pods verified
                ttl 30
                fallthrough in-addr.arpa ip6.arpa
              }
              ...
          }
      kind: ConfigMap
      metadata:
        name: coredns
        namespace: kube-system
                                      
  3. Run the following command in the client pod in ACK Cluster 2 to access Service 1 in ACK Cluster 1:

    curl service1.provider-ns.svc.clusterset.local
  4. (Optional) Modify the dnsConfig.searches field of the client pod in ACK Cluster 2 to access the multi-cluster Service.

    1. Add clusterset.local to the dnsConfig.searches field of the client pod.

      apiVersion: apps/v1
      kind: Deployment
      metadata:
        name: client-pod
        namespace: consumer-ns
      spec:
        ...
        template:
          ...
          spec:
            dnsPolicy: "ClusterFirst"    
            dnsConfig:                   
              searches:                        #dnsConfig. Add clusterset.local. 
                - svc.clusterset.local
                - clusterset.local
                - consumer-ns.svc.cluster.local
                - svc.cluster.local
                - cluster.local
            containers:
            - name: client-pod
              ...
    2. Run the following command to access the multi-cluster Service:

      curl service1.provider-ns

References

You can also configure MCS in the console. For more information, see Use MCS in the ACK One console.