Learn Kubernetes part 1 – Web application in a Kubernetes cluster

This is a tutorial to script a simple web application deployment in an enterprise grade Kubernetes cluster that you can follow on your Macintosh. You only need to install Docker and enable Kubernetes.

The frontend of the web application is represented by an NGINX container that listens on port 80 and returns the NGINX default page. The application is exposed outside of the cluster via a kubernetes/ingress-nginx NGINX Ingress Controller, at the address http://localhost

Save all files in the same directory. During the development process open a terminal in the directory of the files, and periodically test the configuration with kubectl apply -f . to check the code (don’t forget the period at the end of the command). This way Kubernetes will build the system step-by-step giving you continuous feedback.

I have used unique label values to demonstrate which labels make the connection between the resources using the label and selector values. Most of the time the application name is used as label for easy maintenance, but as you learn Kubernetes, it is important to understand the relationships between the resources..

Script the deployment

The deployment configures the containers running in the pods and contains the label that has to match the selector of the service.

Connect the deployment to the pods

The label in spec: selector: matchLabels: connects the deployment to the pods specified in the deployment template via the same deployment’s spec: template: metadata: labels:

app1-frontend-deployment.yam
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app1-frontend-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: app1-frontend-template-label
  template:
    metadata:
      labels:
        app: app1-frontend-template-label
    spec:
      containers:
        - name: app1-frontend-container-label
          image: nginx:1.7.9
          ports:
          - containerPort: 80

Create the pod

Launch the pod from the terminal. Don’t forget the period at the end of the line.

 kubectl apply -f .

Test the pod

To make sure the container in the pod is running, we can test the pod. Get the list of pods

kubectl get pods
NAME          READY   STATUS    RESTARTS   AGE
MY_POD_NAME   1/1     Running   0          10m

Temporarily set up port forwarding to access the pod from outside of the cluster. We only use this to test the pod.

kubectl port-forward MY_POD_NAME 8080:80
Forwarding from 127.0.0.1:8080 -> 80
Forwarding from [::1]:8080 -> 80

Connect to the pod with a web browser. Navigate to http://127.0.0.1:8080/

You should see the NGINX default page.

To stop the port forwarding, press CTRL-C in the terminal.

See Kubernetes Deployments for more info

Script the service

The service specifies the environment variables of the pods backing the service and exposes the pods to the rest of the Kubernetes cluster or to the outside world.

Connect the service to the pods

The label in the service’s spec: selector: has to match the label in spec: template: metadata: labels: of the deployment.

We will expose the service outside of the cluster with type: LoadBalancer

app1-frontend-service.yaml
apiVersion: v1
kind: Service
metadata:
  name: app1-frontend-service
spec:
  selector:
    app: app1-frontend-template-label
  type: LoadBalancer
  ports:
    - protocol: TCP
      port: 8080
      targetPort: 80

See Kubernetes Services for more info.

Create the resources

To launch the application and configure the resources to expose it outside of the Kubernetes cluster, open a terminal in the directory where you saved the files and execute

 kubectl apply -f .

Accessing the application

To access the application get the address of the service

kubectl get service
NAME                    TYPE           CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
app1-frontend-service   LoadBalancer   10.99.210.235   localhost     8080:32569/TCP   9s

Open a web browser and navigate to the address indicated by the EXTERNAL-IP and PORT: http://localhost:8080

You should see the NGINX default page

Delete the resources

If you want to delete these resources from the Kubernetes cluster, execute

kubectl delete -f .

Next: Learn Kubernetes part 2 – NGINX Ingress Controller

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