minimal kubernetes mutating webhook example

introduction

This was a quick exploration of the base primitives that make mutating webhooks in kubernetes function. Assumes a linux host but probably works in other environments with some coaxing.

instructions

1. Run ./start-cluster.sh to create a cluster and tls material for control-plane <-> webhook communication.
2. Install the mutating webhook configuration, deployment and service.

   export CA_BUNDLE=$(cat webhook/pki/ca.crt | base64 | tr -d '\n')
   kubectl kustomize . | envsubst | k apply -f -
   

3. Apply a manifest that satisfies the mutating webhook configuration:

   kubectl apply -f pod.yml
   

4. View that the manifest was modified:

   kubectl get pods -n test --show-labels
   

5. View the request the control plane sends to the webhook:

   kubectl logs deployment/labelmutation
   

6. You can modify the webhook behavior by editing webhook/main.go and re-running step #2.