Kubernetes Clusterip Service Example

Kubernetes ClusterIP Service Example

Kubernetes ClusterIP

cluster ip is the default type of a Kubernetes service. clusterip makes the service only reachable from within the cluster. we can not reach this service from out side the cluster. drawback of using ‘ClusterIp’ is that you cannot call the services from the outside of the cluster without using a proxy. to overcome this issue we have to some proxy. using Kubernetes ingress controller we can expose ClusterIP services to outside the network.

to create a service first we need pods. after creating pods we can expose service with particular labelled pods.

Create Pods:

using kubectl commands we can create pods.

kubectl run mypod  --generator=run-pod/v1 --image=nginx --port=80 --labels="myapp=mynginxapp"

here i created pod name called 'mypod' with label 'myapp=mynginxapp'.

Creating ClusterIP Service:

To create a service we can use kubectl expose command or we can create service with yml file.

apiVersion: v1
kind: Service
metadata:
  name: mynginxsvc
spec:
  type: ClusterIP
  ports:
    - port: 80
      name: http
    - port: 443
      name: https
  selector:
    myapp: mynginxapp

List services

list kubernetes services with kubectl get command

master $ kubectl get svc
NAME         TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
kubernetes   ClusterIP   10.96.0.1       <none>        443/TCP          20m
mynginxsvc   ClusterIP   10.111.129.81   <none>        80/TCP,443/TCP   13s

Here you can see the cluster ip and ports, you can access the nginx app from <clusterip>:<cluster port> i,e 10.111.129.81:80.

from above service of type Cluster-IP is created which would accept traffic on port 80(cluster port) from other pods and forward the traffic on port 80 of the pods with mynginxapp label.

Verify the ClusterIP Service:

kubectl exec -it mypod curl 10.111.129.81:80

using above command you can curl output of nginx app. most of the times curl is not available in nginx pod. so install curl command in your 'mypod'

kubectl exec -it mypod sh

you will enter into shell of mypod, after entering into shell install curl.

apt update -y

apt install curl -y

after installing curl in the pod execute curl <clusterip>:<cluster port>

# curl 10.111.129.81:80
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
</style>

Tip: we can expose a headless service by setting --cluster-ip=None

ClusterIP exposes the service on a cluster-internal IP. This IP address makes the service only reachable from within the cluster.