Creating an MCS Object

Constraints

• MCS is available only in clusters 1.21 or later.
• A Service, with both MCI and Multi-Cluster Service (MCS) configured, can only be delivered to the cluster where the Service is deployed, the cluster that accesses the Service, and the cluster where the corresponding workload is deployed in MCS.

Preparations

• Deploying Workloads and Services

  Deploy available workloads (Deployments) and Services on the federation control plane. If no workload or Service is available, create one by referring to Deployments and ClusterIP.

• Configuring the Cluster Network

  Check and configure the network connectivity of both inter-cluster nodes and containers by referring to Configuring the Multi-Cluster Networking.

Creating an MCS Object

1. Use kubectl to connect to the federation. For details, see Using kubectl to Connect to a Federation.
2. Create and edit an mcs.yaml file. For details about the parameters, see Table 1.

   vi mcs.yaml

   In the example, the defined MCS object is associated with Service foo. This Service is deployed in cluster B and can be accessed from cluster A.

   apiVersion: networking.karmada.io/v1alpha1 
   kind: MultiClusterService 
   metadata: 
      name: foo                          # MCS object name
      namespace: default                  # Name of the namespace where the MCS object is located
   spec: 
      types: 
        - CrossCluster                   # Inter-cluster service discovery
      providerClusters:                  # Cluster that the Service is delivered to
        - name: clusterB
      consumerClusters:                  # Cluster that accesses the Service
        - name: clusterA

   Table 1 Key parameters

   Parameter	Mandatory	Type	Description
   metadata.name	Yes	String	Name of the MCS object, which must be the same as that of the associated Service.
   metadata.namespace	No	String	Name of the namespace where the MCS object is located, which must be the same as that of the namespace where the associated Service is located. If this parameter is left blank, default is used.
   spec.types	Yes	String	Traffic direction. To enable service discovery across clusters, set this parameter to CrossCluster.
   spec.providerClusters.name	No	String	Name of the cluster that the Service is delivered to. Set this parameter to the cluster where the Service is deployed. If this parameter is left blank, the Service is delivered to all clusters in the federation by default. CAUTION: If a Service is deployed in cluster B but cluster A and cluster B are both configured as the delivery targets, the Service is delivered to both clusters. The original Service with the same name in cluster A will be overwritten.
   spec.consumerClusters.name	No	String	Name of the cluster that accesses the Service. Set this parameter to the name of the cluster that is expected to access the Service across clusters through MCS. If this parameter is left blank, all clusters in the federation can access the Service by default.

3. Create an MCS object.

   kubectl apply -f mcs.yaml

4. Check the status of the MCS object (named foo).

   kubectl describe mcs foo

   The status field in the YAML file records the MCS object status. If the following information is displayed, the endpoint slices are successfully delivered and synchronized, and cross-cluster service discovery is available:

   status: 
     conditions: 
     - lastTransitionTime: "2023-11-20T02:30:49Z"  
     message: EndpointSlices are propagated to target clusters. 
       reason: EndpointSliceAppliedSuccess 
       status: "True"  
     type: EndpointSliceApplied

   Run the following commands to operate the MCS object (named foo):

   • kubectl get mcs foo: obtains the MCS object.
   • kubectl edit mcs foo: updates the MCS object.
   • kubectl delete mcs foo: deletes the MCS object.

Cross-Cluster Access

After the MCS object is created, you can access the Service from the cluster specified by consumerClusters.name.

In the cluster specified by consumerClusters.name, create a pod, access the container, and run the curl http://Service name:Port number command to access the Service.

If the following information is displayed, the access is successful:

/ # curl http://Service name:Port number
... 
<h1>Welcome to foo!</h1> 
...