Intra-Cluster Access (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)
Click to enlarge

Adding a Service When Creating a Workload

You can set the access type (Service) when creating a workload on the CCE console.

In the Set Application Access step of Creating a Deployment, Creating a StatefulSet, or Creating a DaemonSet, click Add Service and set the following parameters:
- Access Type: Select ClusterIP.
- Service Name: Specify a Service name, which can be the same as the workload name.
- Port Settings
  - Protocol: protocol used by the Service.
  - Container Port: port on which the workload listens. The Nginx application listens on port 80.
  - Access Port: a port mapped to the container port at the cluster-internal IP address. The workload can be accessed at <cluster-internal IP address>:<access port>. The port number range is 1–65535.
Figure 2 Adding a ClusterIP Service
After the configuration, click OK and then Next: Configure Advanced Settings. On the page displayed, click Create.
Click View Deployment Details or View StatefulSet Details. On the Services tab page, obtain the access address, for example, 10.247.74.100:8080.

Adding a Service After Creating a Workload

You can set the Service after creating a workload. This has no impact on the workload status and takes effect immediately. The procedure is as follows:

Log in to the CCE console. In the navigation pane, choose Workloads > Deployments. On the workload list, click the name of the workload for which you will create a Service.
On the Services tab page, click Add Service.
On the Create Service page, select ClusterIP from the Access Type drop-down list.
Set intra-cluster access parameters.
- Service Name: Service name, which can be the same as the workload name.
- Cluster Name: name of the cluster where the workload runs. The value is inherited from the workload creation page and cannot be changed.
- Namespace: namespace where the workload is located. The value is inherited from the workload creation page and cannot be changed.
- Workload: workload for which you want to add a Service.
- Port Settings
  - Protocol: protocol used by the Service.
  - Container Port: port on which the workload listens. The Nginx application listens on port 80.
  - Access Port: port mapped to the container port at the cluster-internal IP address. The workload can be accessed at <cluster-internal IP address>:<access port>. The port number range is 1–65535.
Click Create. The ClusterIP Service will be added for the workload.

Setting the Access Type Using kubectl

You can run kubectl commands to set the access type (Service). This section uses a 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 a 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 don't 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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