ClusterIP

Scenario

ClusterIP Services allow workloads in the same cluster to use their cluster-internal domain names to access each other.

The cluster-internal domain name format is <Service name>.<Namespace of the workload>.svc.cluster.local:<Port>, for example, nginx.default.svc.cluster.local:80.

Figure 1 shows the access channel and mappings between the access port and container ports.

Figure 1 Intra-cluster access (ClusterIP)

Creating a ClusterIP Service

1. Log in to the CCE console and click the cluster name to access the cluster console.
2. In the navigation pane on the left, choose Services & Ingresses. In the upper right corner, click Create Service.
3. Configure intra-cluster access parameters.
   • Service Name: Specify a Service name, which can be the same as the workload name.
   • Service Type: Select ClusterIP.
   • Namespace: Select the namespace that the workload belongs to.
   • Selector: Add a label and click Confirm. A Service selects a pod based on the added label. You can also click Reference Workload Label to reference the label of an existing workload. In the dialog box that is displayed, select a workload and click OK.
   • Ports
     • Protocol: Select the protocol used by the Service.
     • Service Port: Specify the port used by the Service. The port number ranges from 1 to 65535.
     • Container Port: Specify the port on which the workload listens. For example, Nginx uses port 80 by default.

4. Click OK.

Adding a Service Using kubectl

You can run kubectl commands to add a Service. An Nginx workload is used as an example to describe how to implement intra-cluster access using kubectl.

1. Use kubectl to connect to the cluster. For details, see Connecting to a Cluster Using kubectl.
2. Create and edit the nginx-deployment.yaml and nginx-clusterip-svc.yaml files.

   The file names are user-defined. nginx-deployment.yaml and nginx-clusterip-svc.yaml are merely example file names.

   vi nginx-deployment.yaml

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: nginx
   spec:
     replicas: 1
     selector:
       matchLabels:
         app: nginx
     template:
       metadata:
         labels:
           app: nginx
       spec:
         containers:
         - image: nginx:latest
           name: nginx
         imagePullSecrets:
         - name: default-secret

   vi nginx-clusterip-svc.yaml

   apiVersion: v1
   kind: Service
   metadata:
     labels:
       app: nginx
     name: nginx-clusterip
   spec:
     ports:
     - name: service0
       port: 8080                # Port for accessing a Service
       protocol: TCP             # Protocol used for accessing a Service. The value can be TCP or UDP.
       targetPort: 80            # Port used by a Service to access the target container. This port is closely related to the applications running in a container. In this example, the Nginx image uses port 80 by default.
     selector:                   # Label selector. A Service selects a pod based on the label and forwards the requests for accessing the Service to the pod. In this example, select the pod with the app:nginx label.
       app: nginx
     type: ClusterIP             # Type of a Service. ClusterIP indicates that a Service is only reachable from within the cluster.

3. Create a workload.

   kubectl create -f nginx-deployment.yaml

   If information similar to the following is displayed, the workload has been created.

   deployment "nginx" created

   kubectl get po

   If information similar to the following is displayed, the workload is running.

   NAME                     READY     STATUS             RESTARTS   AGE
   nginx-2601814895-znhbr   1/1       Running            0          15s

4. Create a Service.

   kubectl create -f nginx-clusterip-svc.yaml

   If information similar to the following is displayed, the Service is being created.

   service "nginx-clusterip" created

   kubectl get svc

   If information similar to the following is displayed, the Service has been created, and a cluster-internal IP address has been assigned to the Service.

   # kubectl get svc
   NAME              TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)    AGE
   kubernetes        ClusterIP   10.247.0.1     <none>        443/TCP    4d6h
   nginx-clusterip   ClusterIP   10.247.74.52   <none>        8080/TCP   14m

5. Access the Service.

   A Service can be accessed from containers or nodes in a cluster.

   Create a pod, access the pod, and run the curl command to access the Service over IP address:Port or the domain name.

   The domain name suffix can be omitted. In the same namespace, you can use nginx-clusterip:8080 for access. In other namespaces, you can use nginx-clusterip.default:8080 for access.

   # kubectl run -i --tty --image nginx:alpine test --rm /bin/sh
   If you do not see a command prompt, try pressing Enter.
   / # curl 10.247.74.52:8080
   <!DOCTYPE html>
   <html>
   <head>
   <title>Welcome to nginx!</title>
   <style>
       body {
           width: 35em;
           margin: 0 auto;
           font-family: Tahoma, Verdana, Arial, sans-serif;
       }
   </style>
   </head>
   <body>
   <h1>Welcome to nginx!</h1>
   <p>If you see this page, the nginx web server is successfully installed and
   working. Further configuration is required.</p>
   
   <p>For online documentation and support please refer to
   <a href="http://nginx.org/">nginx.org</a>.<br/>
   Commercial support is available at
   <a href="http://nginx.com/">nginx.com</a>.</p>
   
   <p><em>Thank you for using nginx.</em></p>
   </body>
   </html>
   / # curl nginx-clusterip.default.svc.cluster.local:8080
   ...
   <h1>Welcome to nginx!</h1>
   ...
   / # curl nginx-clusterip.default:8080
   ...
   <h1>Welcome to nginx!</h1>
   ...
   / # curl nginx-clusterip:8080
   ...
   <h1>Welcome to nginx!</h1>
   ...