Previous: kubectl for CKAD - exercise 2 - edit and replace a pod

Getting Started with kubectl for CKAD exam

First things first

Put your mouse away, forget you have a touchpad and keep your hands on the keyboard.

Start your terminal, the adventure continues…

The situation with the CKAD and other CK* exams is that we need to be fast. To be fast when editing YAML files and applying them with kubectl apply means - don’t leave Vim. Yes, we can run kubectl replace right from inside Vim!

Scenario

A pod named colorpod is running in the cluster. It has an environment variable APP_COLOR=red. We want to change the value of APP_COLOR to green.

Run a pod with this command:

kubectl run colorpod --image nginx:alpine --env APP_COLOR=red

Output:

pod/colorpod created

To check the environment variables:

kubectl set env pods colorpod --list

Output:

# Pod colorpod, container colorpod
APP_COLOR=red

Attempting to directly set the environment variable like this throws an error:

kubectl set env pods colorpod APP_COLOR=green

But, there is a way around it!

Use kubectl set env with --dry-run=client to get the colorpod’s YAML manifest and replace the pod

kubectl set env pods colorpod APP_COLOR=green --dry-run=client -o yaml | vim -

Vim opens the YAML file generated by the command above. Notice that the value of the APP_COLOR env variable is green.

Save the document as a new file (for example, new-colorpod.yaml)

:w new-colorpod.yaml

Replace the running pod with the updated definition directly from Vim

:!kubectl replace -f % --force --grace-period 0

If there is an error and the pod has not been replaced, read the error, correct the YAML, and repeat the steps

  1. write (save) the document: 
    ESC        // 'ESC'ape from INSERT mode
:w         // 'w'rite (save) the document
  2. Use the previous kubectl replace command: 
    :up arrow   // repeat to find the command :!kubectl replace -f % --force --grace-period 0
Enter

If everything is fine with the updated pod definition, it will be deleted, and a new pod will be created.

Close the document / quit Vim

:q

Vim quits, closing the edited YAML file.

Check, if the environment variable is set correctly on the newly created pod:

kubectl set env pods colorpod --list

Congratulations!

Practice these steps to master setting pod environment variables and replacing pods directly from Vim with kubectl.

Next: kubectl for CKAD - exercise 4 - set resources and replace pod