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 mapping relationships between access channels, container ports, and access ports.

Figure 1 Intra-cluster access (ClusterIP)

Creating a ClusterIP Service

Log in to the CCE console and click the cluster name to access the cluster console.
In the navigation pane, choose Services & Ingresses. In the upper right corner, click Create Service.
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: Namespace to which the workload belongs.
- Selector: Add a label and click Confirm. The Service will use this label to select pods. You can also click Reference Workload Label to use the label of an existing workload. In the dialog box that is displayed, select a workload and click OK.
- IPv6: This function is disabled by default. After this function is enabled, the cluster IP address of the Service changes to an IPv6 address. For details, see Creating an IPv4/IPv6 Dual-Stack Cluster in CCE. This parameter is available only in clusters of v1.15 or later with IPv6 enabled (set during cluster creation).
- Ports
  - Protocol: protocol used by the Service.
  - Service Port: port used by the Service. The port number ranges from 1 to 65535.
  - Container Port: listener port of the workload. For example, Nginx uses port 80 by default.
Click OK.

Setting the Access Type Using kubectl

You can run kubectl commands to configure Service access. This section uses an Nginx workload as an example to describe how to implement intra-cluster access using kubectl.

Use kubectl to connect to the cluster. For details, see Connecting to a Cluster Using kubectl.

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.

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
```
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
```

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 IP address:Port or the domain name of the Service, as shown in the following figure.

The domain name suffix can be omitted. In the same namespace, you can directly 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>
...

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