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Kubernetes Lab (1 hour)

In this lab, you will deploy your previously created Docker image in Kubernetes.
The goal of this lab is to

  • show you the usage of Kubernetes deployments and services
  • how to use Kubernetes scaling capabilites
  • how to access a service deployed in Kubernetes

Application Deployment

  1. Verify that you can access Kubernetes:

     kubectl version

    If you see a Server Version like below, it means your Kubernetes CLI can connect to your Kubernetes VM:

     $ kubectl version
 Client Version: version.Info{Major:"1", Minor:"13", GitVersion:"v1.13.10", GitCommit:"37d169313237cb4ceb2cc4bef300f2ae3053c1a2", GitTreeState:"clean", BuildDate:"2019-08-19T10:52:43Z", GoVersion:"go1.11.13", Compiler:"gc", Platform:"linux/amd64"}
 Server Version: version.Info{Major:"1", Minor:"13", GitVersion:"v1.13.10", GitCommit:"37d169313237cb4ceb2cc4bef300f2ae3053c1a2", GitTreeState:"clean", BuildDate:"2019-08-19T10:44:49Z", GoVersion:"go1.11.13", Compiler:"gc", Platform:"linux/amd64"}

  2. Download the following file to your "CloudAwarenessLab" folder:

  3. Open the file in an editor and verify that the image: key is referencing your previously built image

  4. Deploy your application with the following command:

     kubectl apply -f deployment.yaml

  5. Verify that your application is running properly:

     kubectl get deployment

    You shoud now see one running Pod, which is scheduled by the Deployment that you just created.

  6. You can also check the running Pods in your Kubernetes cluster by typing:

     kubectl get pods

    This will give a list of running instances (a.k.a. Pods) of your application.
    Write down the name of the Pod, you'll need it later for reference.

  7. In order to access your application, you have to deploy a Kubernetes service.
    Download the following file your "CloudAwarenessLab" folder:

    and apply the following command:

     kubectl apply -f service.yaml

  8. You have now deployed a so called NodePort Kubernetes Service. It opens a dedicated port on your Minikube VM, through which you can access the according service.
    You can find the associated port number by typing:

     kubectl get svc

    In the example below, the port number would be 31478:

     $ kubectl get svc  
 NAME                TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE  
 kubernetes          ClusterIP   10.96.0.1        <none>        443/TCP        126d
 webserver-service   NodePort    10.98.147.142    <none>        80:31478/TCP   4s

  9. In your browser, open the IP of your Minikube VM (which you retrieved in the previous lab) and add the port that you retrieved from the last command, e.g.: http://minikube-ip:31478.
    You should see "Hello World" example from before, but it's hosted in Kubernetes.
    You should also see that the hostname is equal to the Pod name that you wrote down earlier.

Application Scaling

  1. Now you'll see the scaling capabilities of Kubernetes. Enter the following command:

     kubectl scale deployment/webserver-deployment --replicas=3

    With this command, you update the Kubernetes Deployment and instruct it to have a total of three replicas. Kubernetes will handle that by instantiating two additional Pods.

  2. Refresh your browser serveral times and monitor how the hostname of your microservice changes.
    Congratulations, you just learned how to scale a service in Kubernetes.

Application Configuration

  1. For the next step, we we'll see how to configure an application in Kubernetes.
    You might have noticed that in the app.js file, we are defining an environment variable GREETING with the default value Hello World.
    In a first step, we will change the Kubernetes the Kubernetes deployment and add environment variable section the Pod template:

     kubectl edit deployment webserver-deployment

    and add the env section like described below:

     spec:
 containers:
 - image: mywebserver:1.0
   imagePullPolicy: IfNotPresent
   name: webserver
   env:
   - name: GREETING
 	value: "I'm configured now"

  2. Refresh your browser, and see how to greeting changed.

  3. Now let's use another mean to configure our application: the Kubernetes ConfigMap. Download the sample ConfigMap to your "CloudAwarenessLab" folder:

    This way, you can decouple the application from the deployment configuration and therefore ease the reusability of your application. You can deploy the ConfigMap with the following command:

     kubectl apply -f configmap.yaml

  4. Now, you'll have to modify your deployment in order to consume the ConfigMap:

     kubectl edit deployment webserver-deployment

    And edit the file in the following way:

     spec:
 containers:
 - image: mywebserver:1.0
 	imagePullPolicy: IfNotPresent
 	name: webserver
 	env:
 	- name: GREETING
 	valueFrom:
 		configMapKeyRef:
 		name: webserver-configmap
 		key: greeting

Application Secrets

Kubernetes also supports objects of the type Secret, that are meant to store sensitive data. Secrets can either be injected as environment variables or mounted in the Pods filesystem.
As you already learned how to inject environment variables, let's now inject the Kubernetes secret as a file into our pod.

  1. Deploy a secret in our Kubernetes cluster:

     kubectl create secret generic webserver-secret --from-literal=secret.txt="Well done!"

  2. Update your Pod definiton to mount the webserver-secret secret in /var/secret/:

     kubectl edit deployment webserver-deployment

    And edit the file in the following way:

     spec:
 containers:
 - image: mywebserver:1.0
 	imagePullPolicy: IfNotPresent
 	name: webserver
 	volumeMounts:
 	- name: webserver-secret
 	mountPath: "/var/secret"
 	readOnly: true
 volumes:
 - name: webserver-secret
 	secret:
 	secretName: webserver-secret

  3. Refresh your browser, and see how the greeting changed.

Follow up exercise (30 Minutes)

Try to launch a database in Kubernetes and connect an application with this database.
A simple example can be found here. It's written in Node.JS and uses MongoDB.