CKS Supply Chain Security Practice Question
An administrator wants to ensure that only images from a trusted registry 'myregistry.io' can run in the cluster. Which admission controller should be configured?
⚠ Common exam trap
Many candidates confuse PodSecurity (or deprecated PodSecurityPolicy) with image registry control, but PodSecurity only handles pod-level security contexts, not image source validation. ImagePolicyWebhook is the correct admission controller for this purpose.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ImagePolicyWebhook
The ImagePolicyWebhook admission controller enforces that only images from a trusted registry (e.g., 'myregistry.io') can run. It does this by querying an external webhook to validate the image source against a policy. Options A, B, and D are incorrect: NodeRestriction restricts node API access, MutatingAdmissionWebhook can mutate pods but is not specifically designed for image registry control, and PodSecurity handles pod security contexts, not image source validation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
NodeRestriction
Why it's wrong here
NodeRestriction limits which fields a kubelet may modify on its own Node and Pod objects; it never evaluates image registries. Restricting images to myregistry.io requires an admission controller that inspects image references, such as ImagePolicyWebhook or a policy engine.
- ✗
MutatingAdmissionWebhook
Why it's wrong here
MutatingAdmissionWebhook rewrites objects rather than rejecting them, so it cannot block a pod whose image originates outside myregistry.io. It is intended for defaulting and patching fields, such as injecting sidecars or labels, and would be the right choice when admitted resources need automatic modification rather than denial.
- ✓
ImagePolicyWebhook
Why this is correct
ImagePolicyWebhook forwards image admission requests to an external HTTPS endpoint that approves or rejects them. Configuring it to permit only myregistry.io images enforces the trusted-registry constraint at admission time, blocking pods referencing any other registry.
- ✗
PodSecurity
Why it's wrong here
PodSecurity enforces pod-level security standards covering privileged mode, host namespaces and capabilities; it evaluates no image registry field, so it cannot restrict pods to myregistry.io. It is the correct control when the requirement is enforcing the Restricted or Baseline security profile across a namespace.
Go deeper
Related to this question
Learn chapter
Supply Chain Security: Container Image Security
Key term
Node Restriction
A Kubernetes admission controller that limits what a kubelet can modify on its own node to prevent privilege escalation and unauthorized access.
Key term
Admission Controllers
Admission controllers are plugins that intercept and process requests to the Kubernetes API server after authentication and authorization, but before the request is persisted, allowing policies to be enforced on objects being created, modified, or deleted.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CKS practice question is part of Courseiva's free CNCF certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CKS exam.