What is the cluster IP in Kubernetes?

Question

I have created a cluster of three nodes: one master, two minions. How to check the cluster IP in Kubernetes? Is it the IP of the master node?

What do you mean by the "cluster IP"? What is your use case? — Tim Allclair
Was trying to implement service type load-balancer from following link: kubernetes.io/v1.0/docs/user-guide/services.html ,there it asked for cluster-ip . — Madhurima Mishra

Tim Allclair Tim Allclair · Accepted Answer · 2015-11-02T18:31:42

ClusterIP can mean 2 things: a type of service which is only accessible within a Kubernetes cluster, or the internal ("virtual") IP of components within a Kubernetes cluster. Assuming you're asking about finding the internal IP of a cluster, it can be accessed in 3 ways (using the simple-nginx example):

Via command line kubectl utility:

$ kubectl describe service my-nginx
Name:           my-nginx
Namespace:      default
Labels:         run=my-nginx
Selector:       run=my-nginx
Type:           LoadBalancer
IP:         10.123.253.27
LoadBalancer Ingress:   104.197.129.240
Port:           <unnamed>   80/TCP
NodePort:       <unnamed>   30723/TCP
Endpoints:      10.120.0.6:80
Session Affinity:   None
No events.

Via the kubernetes API (here I've used kubectl proxy to route through localhost to my cluster):

$ kubectl proxy &
$ curl -G http://localhost:8001/api/v1/namespaces/default/services/my-nginx
{
  "kind": "Service",
  "apiVersion": "v1",
  "metadata": <omitted>,
  "spec": {
    "ports": [
      {
        "protocol": "TCP",
        "port": 80,
        "targetPort": 80,
        "nodePort": 30723
      }
    ],
    "selector": {
      "run": "my-nginx"
    },
    "clusterIP": "10.123.253.27",
    "type": "LoadBalancer",
    "sessionAffinity": "None"
  },
  "status": {
    "loadBalancer": {
      "ingress": [
        {
          "ip": "104.197.129.240"
        }
      ]
    }
  }
}

Via the $<NAME>_SERVICE_HOST environment variable within a Kubernetes container (in this example my-nginx-yczg9 is the name of a pod in the cluster):
```
$ kubectl exec my-nginx-yczg9 -- sh -c 'echo $MY_NGINX_SERVICE_HOST'
10.123.253.27
```

More details on service IPs can be found in the Services in Kubernetes documentation, and the previously mentioned simple-nginx example is a good example of exposing a service outside your cluster with the LoadBalancer service type.

What is the cluster IP in Kubernetes?

4 Answers