Module 4 - Expose your app publicly

Difficulty: Beginner Estimated Time: 10 minutes

In this scenario you will learn how to expose Kubernetes applications outside the cluster using the kubectl expose command. You will also learn how to view and apply labels to objects with the kubectl label command.

Step 1 - Create a new service

Let’s verify that our application is running. We’ll use the kubectl get command and look for existing Pods:

kubectl get pods

Next, let’s list the current Services from our cluster:

kubectl get services

We have a Service called Kubernetes that is created by default when minikube starts the cluster. To create a new service and expose it to external traffic we’ll use the expose command with NodePort as parameter.

kubectl expose deployment/kubernetes-bootcamp --type="NodePort" --port 8080

Let’s run again the get services command:

kubectl get services

Note for Docker Desktop users: Due to Docker Desktop networking limitations, by default you’re unable to access pods directly from the host. Run minikube service kubernetes-bootcamp, this will create a SSH tunnel from the pod to your host and open a window in your default browser that’s connected to the service. The tunnel can be terminated by pressing control-C, then continue on to Step 2.

We have now a running Service called kubernetes-bootcamp. Here we see that the Service received a unique cluster-IP, an internal port and an external-IP (the IP of the Node).

To find out what port was opened externally (by the NodePort option) we’ll run the describe service command:

kubectl describe services/kubernetes-bootcamp

Create an environment variable called NODE_PORT that has the value of the Node port assigned:

export NODE_PORT=$(kubectl get services/kubernetes-bootcamp -o go-template='{{(index .spec.ports 0).nodePort}}')
echo NODE_PORT=$NODE_PORT

Now we can test that the app is exposed outside of the cluster using curl, the IP of the Node and the externally exposed port:

curl $(minikube ip):$NODE_PORT

And we get a response from the server. The Service is exposed.

Step 2 - Using labels

The Deployment created automatically a label for our Pod. With describe deployment command you can see the name of the label:

kubectl describe deployment

Let’s use this label to query our list of Pods. We’ll use the kubectl get pods command with -l as a parameter, followed by the label values:

kubectl get pods -l app=kubernetes-bootcamp

You can do the same to list the existing services:

kubectl get services -l app=kubernetes-bootcamp

Get the name of the Pod and store it in the POD_NAME environment variable:

export POD_NAME=$(kubectl get pods -o go-template --template '{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}')
echo Name of the Pod: $POD_NAME

To apply a new label we use the label command followed by the object type, object name and the new label:

kubectl label pods $POD_NAME version=v1

This will apply a new label to our Pod (we pinned the application version to the Pod), and we can check it with the describe pod command:

kubectl describe pods $POD_NAME

We see here that the label is attached new to our Pod. And we can query now the list of pods using the new label:

kubectl get pods -l version=v1

And we see the Pod.

Step 3 - Deleting a service

To delete Services you can use the delete service command. Labels can be used also here:

kubectl delete service -l app=kubernetes-bootcamp

Confirm that the service is gone:

kubectl get services

This confirms that our Service was removed. To confirm that route is not exposed anymore you can curl the previously exposed IP and port:

curl $(minikube ip):$NODE_PORT

This proves that the app is not reachable anymore from outside of the cluster. You can confirm that the app is still running with a curl inside the pod:

kubectl exec -ti $POD_NAME -- curl localhost:8080

We see here that the application is up. This is because the Deployment is managing the application. To shut down the application, you would need to delete the Deployment as well.

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