- A
OPA/Gatekeeper
OPA/Gatekeeper can define policies to restrict image registries using a ConstraintTemplate.
- B
Helm
Why wrong: Helm is a package manager, not an admission controller.
- C
Calico
Why wrong: Calico is a network policy tool, not for admission control.
- D
Prometheus
Why wrong: Prometheus is a monitoring tool, not for admission control.
Question 190 of 997
OPA/Gatekeeper: Enforce Image Registry Restrictions
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.
A cluster administrator wants to allow only images from a specific registry (e.g., 'myregistry.io') to be deployed in the cluster. Which tool can be used to enforce this via admission control?
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
✓
OPA/Gatekeeper
OPA/Gatekeeper is a Kubernetes admission controller that allows you to enforce custom policies, such as restricting container images to a specific registry. By defining a ConstraintTemplate and a Constraint that checks the image prefix (e.g., 'myregistry.io/'), Gatekeeper can reject any Pod creation that uses images from unauthorized registries. This directly addresses the requirement for registry-based admission control.
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.
- ✓
OPA/Gatekeeper
Why this is correct
OPA/Gatekeeper can define policies to restrict image registries using a ConstraintTemplate.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Helm
Why it's wrong here
Helm is a package manager, not an admission controller.
- ✗
Calico
Why it's wrong here
Calico is a network policy tool, not for admission control.
- ✗
Prometheus
Why it's wrong here
Prometheus is a monitoring tool, not for admission control.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse Helm (a deployment tool) with an admission controller, or assume Calico (a network policy tool) can enforce image registry restrictions, when only OPA/Gatekeeper or similar admission webhooks can perform this validation.
Detailed technical explanation
How to think about this question
Under the hood, OPA/Gatekeeper uses the Kubernetes Dynamic Admission Control mechanism via a ValidatingWebhookConfiguration. The webhook intercepts Pod create/update requests, and OPA evaluates Rego policies that can inspect the image field (e.g., `input.request.object.spec.containers[_].image`). A subtle behavior is that the policy must also handle initContainers and ephemeral containers, as they can also pull images from unauthorized registries. In a real-world scenario, this prevents supply chain attacks where a compromised container image from an untrusted registry is deployed.
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
- →
Supply Chain Security practice questions
Targeted practice on this topic area only
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All CKS questions
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Certified Kubernetes Security Specialist CKS study guide
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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: OPA/Gatekeeper — OPA/Gatekeeper is a Kubernetes admission controller that allows you to enforce custom policies, such as restricting container images to a specific registry. By defining a ConstraintTemplate and a Constraint that checks the image prefix (e.g., 'myregistry.io/'), Gatekeeper can reject any Pod creation that uses images from unauthorized registries. This directly addresses the requirement for registry-based admission control.
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 admin runs 'kubectl run nginx --image=nginx' and the pod fails with 'ImagePullBackOff'. The cluster has an OPA/Gatekeeper constraint that only allows images from 'myregistry.io'. How can the admin quickly test the restriction?
medium- A.Delete the OPA constraint
- B.Add a label 'allowlist=true' to the pod
- ✓ C.Use an image from 'myregistry.io/nginx:latest'
- D.Use 'kubectl run nginx --image=nginx --validate=false'
Why C: Option C is correct because the OPA/Gatekeeper constraint explicitly restricts allowed images to those from 'myregistry.io'. By specifying an image from that registry (e.g., 'myregistry.io/nginx:latest'), the admin can quickly verify that the constraint permits compliant images. This tests the policy's intended behavior without altering or bypassing the constraint.
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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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