Hands-on Lab·Certified Kubernetes Security Specialist
Restricting Permitted Image Registries
Securing a supply chain means deciding what the cluster will run before it runs it. This guide writes a policy that permits two registries and requires a digest, shows each rule refusing something different, and is clear about what admission control cannot check.
Supply Chain Security Guide 28 of 40 Intermediate
- Kubernetesapiserver v1.36.4, kubelet v1.36.3
- Runtimecontainerd 2.2.6
- CNICilium 1.18.1 - tunnel/VXLAN, with Hubble relay and UI
- Host OSUbuntu 26.04 LTS, kernel 7.0.0-29
- Built withkubeadm v1.36.3 - podSubnet 10.244.0.0/16, serviceSubnet 10.96.0.0/12
- TimeAbout 16 min
- Reviewed25 August 2026
Written against the versions above. ValidatingAdmissionPolicy with CEL, built into the apiserver. It evaluates the object in front of it and cannot make a network call, which decides what this control can and cannot do.
| Server Name | IP Address | OS | Roles | CPU | RAM | HDD |
|---|---|---|---|---|---|---|
| CKA6001 | 192.168.0.46 | Ubuntu 26.04 LTS | Control Plane Node (tainted NoSchedule) | 2 Core | 4 GB | 50 GB |
| CKA6001-NODE01 | 192.168.0.47 | Ubuntu 26.04 LTS | Worker Node | 2 Core | 4 GB | 50 GB |
| CKA6001-NODE02 | 192.168.0.48 | Ubuntu 26.04 LTS | Worker Node | 2 Core | 4 GB | 50 GB |
Before you start
- guide 33 - why the digest rule exists.
-
The cluster will run anything from anywhere
-
One policy, two rules
-
Three attempts
-
What this policy cannot do
-
The plugin the exam still asks about