Whenever I need to update a YAML file, the first thing that comes to mind is to either use sed or awk or perl etc., But there's an in-house kubectl patch option that simplifies the experience.

Lab Setup

You can start the lab setup by clicking on the Lab Setup button on the right side of the screen. Please note that there are app-specific URLs exposed specifically for the hands-on lab purpose.

Our lab has been set up with all necessary tools like base OS (Ubuntu), and developer tools like Git, Vim, wget, and others. 

Lab With Kubectl Patch

As we triggered the lab through the LAB SETUP button, a terminal, and an IDE comes for us which already have a Kubernetes cluster running in them. This can be checked by running the kubectl get nodes command.    

Creating Kubernetes Deployment

• First, let’s create the nginx-deployment with 2 replicas and with container image as nginx with alpine tag.

Apply the above nginx-deployment.yaml file and then check deployments and pods

kubectl apply -f nginx-deployment.yaml

kubectl get deployments

kubectl get pods

Now, let’s update the number of replicas in the spec  and also the nginx container image version. Remember, it's multiline, and using any other option can be a bit clumsy.    

Updating Kubernetes Deployment

• Locally, let’s create a file called patch.yaml with the below content.

Then patch the nginx-deployment with the below command

kubectl patch deployment/nginx-deployment --patch "$(cat patch.yaml)"

Once you see this message deployment.apps/nginx-deployment patched. Run the below command to check the deployments

kubectl get deployments

kubectl get pods

kubectl get deployment nginx-deployment -o yaml

and look for to see the previous configuration that is replaced 

What Next?

As we have seen an example about how to patch an existing deployment with a kubectl patch, more information on this can be found out here.

Conclusion

In this hands-on lab, we learned how to update existing Kubernetes resources with the kubectl patch command.