- A
violation[{"msg": "Running as root is not allowed"}] { input.review.object.spec.containers[_].securityContext.capabilities.drop == "ALL" }
Why wrong: This checks for dropping ALL capabilities, not the user ID.
- B
violation[{"msg": "Running as root is not allowed"}] { input.review.object.spec.securityContext.runAsUser == 0 }
Why wrong: This only checks pod-level securityContext, not container-level, and uses incorrect field path (should be container level).
- C
violation[{"msg": "Running as root is not allowed"}] { input.review.object.spec.containers[_].securityContext.runAsUser == 0 }
This correctly denies pods with runAsUser=0.
- D
violation[{"msg": "Running as root is not allowed"}] { input.review.object.spec.containers[_].securityContext.runAsNonRoot == true }
Why wrong: This denies pods that set runAsNonRoot: true, which is the opposite of what we want.
OPA Gatekeeper Rego Policy to Deny Containers Running as Root (runAsUser: 0)
This CKS practice question tests your understanding of minimize microservice vulnerabilities. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
Which of the following OPA Gatekeeper Rego policies would deny a pod that sets `securityContext.runAsUser: 0`?
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
violation[{"msg": "Running as root is not allowed"}] { input.review.object.spec.containers[_].securityContext.runAsUser == 0 }
Option C is correct because it uses the correct Rego path to match the `runAsUser` field inside each container's `securityContext`. The `containers[_]` iterator ensures the policy checks every container in the pod spec, and `runAsUser == 0` correctly identifies containers running as root. This is the standard way to enforce a 'no root' policy at the container level in OPA Gatekeeper.
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.
- ✗
violation[{"msg": "Running as root is not allowed"}] { input.review.object.spec.containers[_].securityContext.capabilities.drop == "ALL" }
Why it's wrong here
This checks for dropping ALL capabilities, not the user ID.
- ✗
violation[{"msg": "Running as root is not allowed"}] { input.review.object.spec.securityContext.runAsUser == 0 }
Why it's wrong here
This only checks pod-level securityContext, not container-level, and uses incorrect field path (should be container level).
- ✓
violation[{"msg": "Running as root is not allowed"}] { input.review.object.spec.containers[_].securityContext.runAsUser == 0 }
Why this is correct
This correctly denies pods with runAsUser=0.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
violation[{"msg": "Running as root is not allowed"}] { input.review.object.spec.containers[_].securityContext.runAsNonRoot == true }
Why it's wrong here
This denies pods that set runAsNonRoot: true, which is the opposite of what we want.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The CKS exam often tests the distinction between pod-level and container-level `securityContext` fields, and candidates mistakenly choose option B because they assume `runAsUser` can be set at the pod level, but it is only valid inside `containers[].securityContext`.
Detailed technical explanation
How to think about this question
In Kubernetes, `securityContext.runAsUser` is defined at the container level (in `spec.containers[].securityContext`), not at the pod level (the pod-level `securityContext` has fields like `runAsUser` for init containers or `fsGroup`, but the main container `runAsUser` is per-container). OPA Gatekeeper uses the `AdmissionReview` object where `input.review.object.spec.containers` is an array; the `[_]` syntax iterates over all elements. A real-world scenario is a cluster with a 'restricted' Pod Security Standard where containers must not run as root; this policy would block any container with `runAsUser: 0` even if other containers are non-root.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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.
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Minimize Microservice Vulnerabilities — study guide chapter
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FAQ
Questions learners often ask
What does this CKS question test?
Minimize Microservice Vulnerabilities — This question tests Minimize Microservice Vulnerabilities — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: violation[{"msg": "Running as root is not allowed"}] { input.review.object.spec.containers[_].securityContext.runAsUser == 0 } — Option C is correct because it uses the correct Rego path to match the `runAsUser` field inside each container's `securityContext`. The `containers[_]` iterator ensures the policy checks every container in the pod spec, and `runAsUser == 0` correctly identifies containers running as root. This is the standard way to enforce a 'no root' policy at the container level in OPA Gatekeeper.
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.
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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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