Module 6 - Update your app

Difficulty: Beginner Estimated Time: 10 minutes

The goal of this scenario is to update a deployed application with kubectl set image and to rollback with the rollout undo command.

Step 1 - Update the version of the app

To list your deployments, run the get deployments command:

kubectl get deployments

To list the running Pods, run the get pods command:

kubectl get pods

To view the current image version of the app, run the describe pods command and look for the Image field:

kubectl describe pods

To update the image of the application to version 2, use the set image command, followed by the deployment name and the new image version:

kubectl set image deployments/kubernetes-bootcamp kubernetes-bootcamp=jocatalin/kubernetes-bootcamp:v2

The command notified the Deployment to use a different image for your app and initiated a rolling update. Check the status of the new Pods, and view the old one terminating with the get pods command:

kubectl get pods

Step 2 - Verify an update

First, check that the app is running. To find the exposed IP and Port, run the describe service command:

kubectl describe services/kubernetes-bootcamp

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 the tutorial after the curl $(minikube ip):$NODE_PORT command.

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}}')

Next, do a curl to the exposed IP and port:

curl $(minikube ip):$NODE_PORT

Every time you run the curl command, you will hit a different Pod. Notice that all Pods are running the latest version (v2).

You can also confirm the update by running the rollout status command:

kubectl rollout status deployments/kubernetes-bootcamp

To view the current image version of the app, run the describe pods command:

kubectl describe pods

In the Image field of the output, verify that you are running the latest image version (v2).

Step 3 - Rollback an update

Let’s perform another update, and deploy an image tagged with v10:

kubectl set image deployments/kubernetes-bootcamp

Use get deployments to see the status of the deployment:

kubectl get deployments

Notice that the output doesn’t list the desired number of available Pods. Run the get pods command to list all Pods:

kubectl get pods

Notice that some of the Pods have a status of ImagePullBackOff.

To get more insight into the problem, run the describe pods command:

kubectl describe pods

In the Events section of the output for the affected Pods, notice that the v10 image version did not exist in the repository.

To roll back the deployment to your last working version, use the rollout undo command:

kubectl rollout undo deployments/kubernetes-bootcamp

The rollout undo command reverts the deployment to the previous known state (v2 of the image). Updates are versioned and you can revert to any previously known state of a deployment.

Use the get pods commands to list the Pods again:

kubectl get pods

Four Pods are running. To check the image deployed on these Pods, use the describe pods command:

kubectl describe pods

The deployment is once again using a stable version of the app (v2). The rollback was successful.

Last modified May 5, 2023: site: Kubernetes 101 tutorial (6134ad5e4)