- A
Use OPA/Gatekeeper to create a constraint that checks the image registry
Gatekeeper can enforce policies on images, including allowing only certain registries.
- B
Set up a NetworkPolicy to block traffic from other registries
Why wrong: NetworkPolicy controls network traffic between pods, not image registries.
- C
Configure an ImagePolicyWebhook
Why wrong: ImagePolicyWebhook is used for verifying image signatures, not for registry allowlisting.
- D
Modify the kubelet configuration to only pull from a specific registry
Why wrong: The kubelet does not have a built-in feature to restrict registries; this is typically done at the admission level.
Question 900 of 997
Restricting Container Images to a Trusted Registry: OPA Gatekeeper vs ImagePolicyWebhook
This CKS practice question tests your understanding of supply chain security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You want to allow only images from a specific registry (e.g., myregistry.io) to be deployed in your cluster. Which tool or approach is best suited for this requirement?
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
✓
Use OPA/Gatekeeper to create a constraint that checks the image registry
OPA/Gatekeeper allows you to define a ConstraintTemplate and a Constraint that validates the image registry in pod specs via a Rego rule. This approach enforces admission control at the API server level, rejecting any pod that references an image from an unauthorized registry before it is persisted in etcd.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Use OPA/Gatekeeper to create a constraint that checks the image registry
Why this is correct
Gatekeeper can enforce policies on images, including allowing only certain registries.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Set up a NetworkPolicy to block traffic from other registries
Why it's wrong here
NetworkPolicy controls network traffic between pods, not image registries.
- ✗
Configure an ImagePolicyWebhook
Why it's wrong here
ImagePolicyWebhook is used for verifying image signatures, not for registry allowlisting.
- ✗
Modify the kubelet configuration to only pull from a specific registry
Why it's wrong here
The kubelet does not have a built-in feature to restrict registries; this is typically done at the admission level.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common misconception is that NetworkPolicy can control image sources, but NetworkPolicy operates on network traffic, not on admission of pod specifications.
Detailed technical explanation
How to think about this question
Under the hood, OPA/Gatekeeper intercepts AdmissionReview requests via a MutatingAdmissionWebhook or ValidatingAdmissionWebhook. The Rego rule typically parses the `spec.containers[*].image` field, extracts the registry hostname (e.g., using `regex.split` or `startswith`), and denies the request if the registry does not match the allowed list. A subtle behavior is that the rule must also handle initContainers, ephemeralContainers, and image references with implicit Docker Hub (e.g., `nginx` expands to `docker.io/library/nginx`), so the Rego policy must explicitly block or allow the default registry.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the CKS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
- →
Supply Chain Security — study guide chapter
Learn the concepts, then practise the questions
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FAQ
Questions learners often ask
What does this CKS question test?
Supply Chain Security — This question tests Supply Chain Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use OPA/Gatekeeper to create a constraint that checks the image registry — OPA/Gatekeeper allows you to define a ConstraintTemplate and a Constraint that validates the image registry in pod specs via a Rego rule. This approach enforces admission control at the API server level, rejecting any pod that references an image from an unauthorized registry before it is persisted in etcd.
What should I do if I get this CKS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on CKS
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An OPA/Gatekeeper constraint is configured to allow only images from 'trusted-registry.io'. A pod is created with image 'trusted-registry.io/app:v1' but is denied. Which is the MOST likely cause?
hard- A.The constraint is only applied in the default namespace
- B.The image tag is not pinned to a digest
- C.The image is not signed
- ✓ D.The constraint uses regex and the image does not match the pattern
Why D: The most likely cause is that the OPA/Gatekeeper constraint uses a regex pattern to match allowed image registries, and the image 'trusted-registry.io/app:v1' does not match that pattern. Gatekeeper constraints often rely on Rego rules that check image strings against regex patterns; if the pattern is too restrictive or incorrectly defined (e.g., requiring a trailing slash or specific path), valid images can be denied. This is a common misconfiguration where the regex does not account for the full image reference format.
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Last reviewed: Jul 4, 2026
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.
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