Exposing an External IP Address to Access an Application in a Cluster

This page shows how to create a Kubernetes Service object that exposes an external IP address.

Before you begin

  • Install kubectl.

  • Use a cloud provider like Google Kubernetes Engine or Amazon Web Services to create a Kubernetes cluster. This tutorial creates an external load balancer, which requires a cloud provider.

  • Configure kubectl to communicate with your Kubernetes API server. For instructions, see the documentation for your cloud provider.

Objectives

  • Run five instances of a Hello World application.
  • Create a Service object that exposes an external IP address.
  • Use the Service object to access the running application.

Creating a service for an application running in five pods

  1. Run a Hello World application in your cluster:

service/load-balancer-example.yaml Exposing an External IP Address to Access an Application in a Cluster - 图1

  1. apiVersion: apps/v1
  2. kind: Deployment
  3. metadata:
  4.   labels:
  5.     app.kubernetes.io/name: load-balancer-example
  6.   name: hello-world
  7. spec:
  8.   replicas: 5
  9.   selector:
  10.     matchLabels:
  11.       app.kubernetes.io/name: load-balancer-example
  12.   template:
  13.     metadata:
  14.       labels:
  15.         app.kubernetes.io/name: load-balancer-example
  16.     spec:
  17.       containers:
  18.       - image: gcr.io/google-samples/node-hello:1.0
  19.         name: hello-world
  20.         ports:
  21.         - containerPort: 8080
  1. kubectl apply -f https://k8s.io/examples/service/load-balancer-example.yaml

The preceding command creates a Deployment and an associated ReplicaSet. The ReplicaSet has five Pods each of which runs the Hello World application.

  1. Display information about the Deployment:

    1.  kubectl get deployments hello-world
    2.  kubectl describe deployments hello-world

  2. Display information about your ReplicaSet objects:

    1.  kubectl get replicasets
    2.  kubectl describe replicasets

  3. Create a Service object that exposes the deployment:

    1.  kubectl expose deployment hello-world --type=LoadBalancer --name=my-service

  4. Display information about the Service:

    1.  kubectl get services my-service

    The output is similar to this:

    1.  NAME         TYPE           CLUSTER-IP     EXTERNAL-IP      PORT(S)    AGE
    2.  my-service   LoadBalancer   10.3.245.137   104.198.205.71   8080/TCP   54s

    Note: The type=LoadBalancer service is backed by external cloud providers, which is not covered in this example, please refer to this page for the details.

    Note: If the external IP address is shown as <pending>, wait for a minute and enter the same command again.

  5. Display detailed information about the Service:

    1.  kubectl describe services my-service

    The output is similar to this:

    1.  Name:           my-service
    2.  Namespace:      default
    3.  Labels:         app.kubernetes.io/name=load-balancer-example
    4.  Annotations:    <none>
    5.  Selector:       app.kubernetes.io/name=load-balancer-example
    6.  Type:           LoadBalancer
    7.  IP:             10.3.245.137
    8.  LoadBalancer Ingress:   104.198.205.71
    9.  Port:           <unset> 8080/TCP
    10.  NodePort:       <unset> 32377/TCP
    11.  Endpoints:      10.0.0.6:8080,10.0.1.6:8080,10.0.1.7:8080 + 2 more...
    12.  Session Affinity:   None
    13.  Events:         <none>

    Make a note of the external IP address (LoadBalancer Ingress) exposed by your service. In this example, the external IP address is 104.198.205.71. Also note the value of Port and NodePort. In this example, the Port is 8080 and the NodePort is 32377.

  6. In the preceding output, you can see that the service has several endpoints: 10.0.0.6:8080,10.0.1.6:8080,10.0.1.7:8080 + 2 more. These are internal addresses of the pods that are running the Hello World application. To verify these are pod addresses, enter this command:

    1.  kubectl get pods --output=wide

    The output is similar to this:

    1.  NAME                         ...  IP         NODE
    2.  hello-world-2895499144-1jaz9 ...  10.0.1.6   gke-cluster-1-default-pool-e0b8d269-1afc
    3.  hello-world-2895499144-2e5uh ...  10.0.1.8   gke-cluster-1-default-pool-e0b8d269-1afc
    4.  hello-world-2895499144-9m4h1 ...  10.0.0.6   gke-cluster-1-default-pool-e0b8d269-5v7a
    5.  hello-world-2895499144-o4z13 ...  10.0.1.7   gke-cluster-1-default-pool-e0b8d269-1afc
    6.  hello-world-2895499144-segjf ...  10.0.2.5   gke-cluster-1-default-pool-e0b8d269-cpuc

  7. Use the external IP address (LoadBalancer Ingress) to access the Hello World application:

    1.  curl http://<external-ip>:<port>

    where <external-ip> is the external IP address (LoadBalancer Ingress) of your Service, and <port> is the value of Port in your Service description. If you are using minikube, typing minikube service my-service will automatically open the Hello World application in a browser.

    The response to a successful request is a hello message:

    1.  Hello Kubernetes!

Cleaning up

To delete the Service, enter this command:

  1. kubectl delete services my-service

To delete the Deployment, the ReplicaSet, and the Pods that are running the Hello World application, enter this command:

  1. kubectl delete deployment hello-world

What’s next

Learn more about connecting applications with services.