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Lab 3 - Deployment

Deployments allow you to manage Pods. With this resource, you'll be able to update and scale quickly and easily your applications.

From now on, we'll be interacting with the cluster thanks to the kubectl command.

Deploy the application

In this lab, we're going to deploy the whoami application. It's a tiny webserver that prints out information about the node it's deployed on.

To do that, we're going to apply the yaml descriptor tp2-deploy-whoami.yaml :

kubectl apply -f tp3-deploy-whoami.yaml

As you can see in the yaml, this descriptor will create a deployment called whoami. This deployment is going to control 3 pod replicas based on the whoami docker image.

Check

  • Check that the deployment was successfully applied
kubectl rollout status deploy whoami
# It should print the following
deployment "whoami" successfully rolled out
  • List all your deployments
kubectl get deploy
# It should print something similar to below
NAME     READY   UP-TO-DATE   AVAILABLE   AGE
whoami   3/3     3            3           5m4s

Here you can see your whoami deployment. You can also see the number of replicas currently running.

  • Get the details of that deployments
kubectl describe deploy whoami

This commands allows to get more info about your deployment, especially the number of replicas and the pod template.

  • List the pods
kubectl get po
# It should print something similar to below
NAME                          READY   STATUS    RESTARTS   AGE
pod/whoami-66688d8f77-7cg4r   1/1     Running   0          14m
pod/whoami-66688d8f77-mh946   1/1     Running   0          14m
pod/whoami-66688d8f77-w9pxj   1/1     Running   0          14m

Here you can see that 3 pods were created as requested.

  • Now what happens if we delete a pod ? Lets try it.
  1. Pick a pod from the previous command and delete it
kubectl delete po whoami-66688d8f77-w9pxj
  1. Now let's print the pods again
kubectl get po
# It should print something similar to below
NAME                      READY   STATUS    RESTARTS   AGE
whoami-66688d8f77-7cg4r   1/1     Running   0          21m
whoami-66688d8f77-dbs5j   1/1     Running   0          8s
whoami-66688d8f77-mh946   1/1     Running   0          21m

As you can see, you still have 3 replicas. Also note that the age is different on one pod. That's the one that the deployment created automatically when you deleted a pod. Why ? Because in your deployment descriptor, you requested 3 replicas. So whatever happens, the kubernetes controller manager will do everything to maintain that number.

  • Change the number of replicas :
# Lets increase the number of replicas
kubectl scale deploy whoami --replicas=5
# Get the deployment again
kubectl get deploy whoami
# It should print something like below
NAME     READY   UP-TO-DATE   AVAILABLE   AGE
whoami   5/5     5            5           28m

As you can see, there is now 5 replicas attached to your deployment.

Now go ahead and print all the pods !