Creating a Mutating Admission Controller Webhook for Kubernetes

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Creating a Mutating Admission Controller Webhook for Kubernetes

Admission controllers affect what actions we let occur on our Kubernetes clusters, either by validating and approving or denying them, or by changing the actual API request objects itself. To alter these objects, we leverage a MutatingAdmissionsWebhook, which parses and updates the object before validation and deployment. In this lab, we'll write one of these webhooks!

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Lab Info

Level

Intermediate

Last updated

Sep 20, 2025

Duration

30m

Challenge

Write Response

Within the webhooks/label-add-webhook/ directory, update the app/server.js file to create a response object.
Challenge

Create JSON Patch

Generate a file containing the label information in the appropriate format. Encode it and add it to the response object.
Challenge

Deploy and Test
If using your own image:
1. Generate certs.
2. Update label-add-webhook-registration.yaml with the Base64-encoded output of app/ca.crt.
3. Log in to Docker; tag and push to repo.
4. Update label-add-webhook-deploy.yaml with your user name instead of linuxacademycontent.
5. Deploy webhook and test as described in the instructions.
If using the provided test image: Deploy webhook as described in the instructions.

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