- A
Validating webhooks should run before mutating webhooks
Correct. This describes the issue exactly: validating webhooks should run before mutating webhooks, but the fixed order causes them to run after, leading to the sidecar being added even when the image is rejected.
- B
Use a validating webhook instead of ImagePolicyWebhook
Why wrong: Wrong. Substituting ImagePolicyWebhook with a validating webhook does not change the order; mutating webhooks still run first.
- C
The mutating webhook should be configured to skip pods with certain images
Why wrong: Wrong. Configuring the mutating webhook to skip certain images is a potential workaround but does not address the fundamental ordering issue.
- D
The ImagePolicyWebhook should be placed before the mutating webhook in the webhook configuration
Why wrong: Wrong. In Kubernetes, the order of admission controllers is fixed: mutating controllers run before validating ones. You cannot reorder ImagePolicyWebhook before the mutating webhook in the plugin chain.
Admission Controller Order: Why Mutating Webhooks Run Before Validating
This CKS practice question tests your understanding of supply chain security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: admission controller ordering. 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 has both ImagePolicyWebhook and a mutating webhook that adds a sidecar. The admin notices that even when ImagePolicyWebhook rejects an image, the mutating webhook has already added the sidecar. What admission ordering issue is occurring?
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
Validating webhooks should run before mutating webhooks
Option A is correct. In Kubernetes, admission controllers are invoked in a fixed order: mutating admission controllers (including MutatingAdmissionWebhook) run before validating ones (including ImagePolicyWebhook and ValidatingAdmissionWebhook). Therefore, the mutating webhook that adds the sidecar runs before ImagePolicyWebhook validates the image. This means even if ImagePolicyWebhook rejects the image, the sidecar has already been added. The issue is that validating webhooks should run before mutating webhooks to prevent such problems, but the fixed order prevents this. Option B is wrong because using a validating webhook still runs after mutating webhooks. Option C is a workaround but not related to the ordering issue. Option D is incorrect because you cannot change the order of built-in admission controllers; the order is fixed.
Key principle: Admission controller ordering
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Validating webhooks should run before mutating webhooks
Why this is correct
Correct. This describes the issue exactly: validating webhooks should run before mutating webhooks, but the fixed order causes them to run after, leading to the sidecar being added even when the image is rejected.
Related concept
Admission controller ordering
- ✗
Use a validating webhook instead of ImagePolicyWebhook
Why it's wrong here
Wrong. Substituting ImagePolicyWebhook with a validating webhook does not change the order; mutating webhooks still run first.
- ✗
The mutating webhook should be configured to skip pods with certain images
Why it's wrong here
Wrong. Configuring the mutating webhook to skip certain images is a potential workaround but does not address the fundamental ordering issue.
- ✗
The ImagePolicyWebhook should be placed before the mutating webhook in the webhook configuration
Why it's wrong here
Wrong. In Kubernetes, the order of admission controllers is fixed: mutating controllers run before validating ones. You cannot reorder ImagePolicyWebhook before the mutating webhook in the plugin chain.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap is that candidates think they can reorder admission controllers, but Kubernetes enforces a fixed order: mutating runs before validating. Therefore, placing a validating controller before a mutating one is not possible.
Detailed technical explanation
How to think about this question
Kubernetes admission webhooks are invoked in two phases: mutating webhooks (which can modify objects) run first, followed by validating webhooks (which can only reject). The ImagePolicyWebhook is a validating webhook, so it runs after the mutating webhook that adds the sidecar. To enforce image policy before mutation, you would need to use a mutating webhook that performs the image check and rejects the request before the sidecar is added, or reorder the webhooks using the 'matchConditions' or 'objectSelector' fields, but the standard ordering is fixed by the API server.
KKey Concepts to Remember
- Admission controller ordering
- ImagePolicyWebhook
- MutatingAdmissionWebhook
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
Admission controller ordering
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. Admission controller ordering 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.
Review admission controller ordering, then practise related CKS questions on the same topic to reinforce the concept.
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Supply Chain Security — study guide chapter
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Supply Chain Security practice 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 — Admission controller ordering.
What is the correct answer to this question?
The correct answer is: Validating webhooks should run before mutating webhooks — Option A is correct. In Kubernetes, admission controllers are invoked in a fixed order: mutating admission controllers (including MutatingAdmissionWebhook) run before validating ones (including ImagePolicyWebhook and ValidatingAdmissionWebhook). Therefore, the mutating webhook that adds the sidecar runs before ImagePolicyWebhook validates the image. This means even if ImagePolicyWebhook rejects the image, the sidecar has already been added. The issue is that validating webhooks should run before mutating webhooks to prevent such problems, but the fixed order prevents this. Option B is wrong because using a validating webhook still runs after mutating webhooks. Option C is a workaround but not related to the ordering issue. Option D is incorrect because you cannot change the order of built-in admission controllers; the order is fixed.
What should I do if I get this CKS question wrong?
Review admission controller ordering, then practise related CKS questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Admission controller ordering
About these practice questions
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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. Which THREE of the following are correct statements about Kubernetes admission controllers in the context of supply chain security? (Select 3)
hard- ✓ A.Admission controllers are executed in a specific order that can affect the final state of the resource
- ✓ B.ValidatingAdmissionWebhook can be used to enforce policies like requiring all images to be signed
- C.MutatingAdmissionWebhook can only modify pods, not other resources
- ✓ D.ImagePolicyWebhook is used to validate container images against an external policy
- E.OPA/Gatekeeper uses MutatingAdmissionWebhook to enforce policies
Why A: Admission controllers are executed in a specific order: mutating controllers run first, then validating controllers. This ordering is critical because a mutating webhook can modify the resource before a validating webhook evaluates it, potentially bypassing intended policies if the order is not carefully managed. The Kubernetes API server processes admission controllers sequentially based on the order defined in the API server flags or the built-in chain, which directly affects the final resource state.
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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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