- A
violation[{"msg": msg}] { container := input.review.object.spec.containers[_] container.securityContext.readOnlyRootFilesystem == true msg := "readOnlyRootFilesystem must be true" }
Why wrong: This denies pods that DO have readOnlyRootFilesystem true, which is opposite.
- B
violation[{"msg": msg}] { container := input.review.object.spec.containers[_] not container.securityContext.readOnlyRootFilesystem msg := "readOnlyRootFilesystem must be true" }
Correctly denies when readOnlyRootFilesystem is not set or false.
- C
violation[{"msg": msg}] { container := input.review.object.spec.containers[_] not container.securityContext.readOnlyRootFilesystem == false msg := "readOnlyRootFilesystem must be true" }
Why wrong: This is a double negative and still incorrect logic.
- D
violation[{"msg": msg}] { container := input.review.object.spec.containers[_] container.securityContext.readOnlyRootFilesystem == false msg := "readOnlyRootFilesystem must be true" }
Why wrong: This only denies when explicitly false, but not when the field is missing.
Writing Rego Rules to Enforce readOnlyRootFilesystem with Gatekeeper
This CKS practice question tests your understanding of minimize microservice vulnerabilities. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 are using Open Policy Agent (OPA) Gatekeeper to enforce pod security. You want to create a constraint that denies pods unless they have readOnlyRootFilesystem set to true. Which Rego rule in a ConstraintTemplate correctly implements this?
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": msg}] { container := input.review.object.spec.containers[_] not container.securityContext.readOnlyRootFilesystem msg := "readOnlyRootFilesystem must be true" }
Option B is correct because it uses `not container.securityContext.readOnlyRootFilesystem` to trigger a violation when the field is missing, false, or nil. In Rego, `not` succeeds when the expression inside it fails, so this rule denies any pod where any container does not have `readOnlyRootFilesystem` explicitly set to `true`. This matches the requirement to deny pods unless the field is `true`.
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": msg}] { container := input.review.object.spec.containers[_] container.securityContext.readOnlyRootFilesystem == true msg := "readOnlyRootFilesystem must be true" }
Why it's wrong here
This denies pods that DO have readOnlyRootFilesystem true, which is opposite.
- ✓
violation[{"msg": msg}] { container := input.review.object.spec.containers[_] not container.securityContext.readOnlyRootFilesystem msg := "readOnlyRootFilesystem must be true" }
Why this is correct
Correctly denies when readOnlyRootFilesystem is not set or false.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
violation[{"msg": msg}] { container := input.review.object.spec.containers[_] not container.securityContext.readOnlyRootFilesystem == false msg := "readOnlyRootFilesystem must be true" }
Why it's wrong here
This is a double negative and still incorrect logic.
- ✗
violation[{"msg": msg}] { container := input.review.object.spec.containers[_] container.securityContext.readOnlyRootFilesystem == false msg := "readOnlyRootFilesystem must be true" }
Why it's wrong here
This only denies when explicitly false, but not when the field is missing.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CNCF often tests the nuance that `not` in Rego catches both `false` and undefined values, whereas an explicit `== false` check misses undefined fields — a common pitfall for candidates who think only explicit `false` values should be denied.
Detailed technical explanation
How to think about this question
In OPA Gatekeeper, the `violation` rule in a ConstraintTemplate is evaluated for each container in the pod spec. The `not` operator in Rego performs negation-as-failure: it succeeds only if the inner expression produces no bindings. When `securityContext` or `readOnlyRootFilesystem` is undefined, `container.securityContext.readOnlyRootFilesystem` evaluates to `undefined`, which causes `container.securityContext.readOnlyRootFilesystem == true` to fail — so `not` catches that case. This is critical because a missing field is semantically equivalent to `false` in Kubernetes security contexts.
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.
- →
Minimize Microservice Vulnerabilities — study guide chapter
Learn the concepts, then practise the questions
- →
Minimize Microservice Vulnerabilities practice questions
Targeted practice on this topic area only
- →
All CKS questions
997 questions across all exam domains
- →
Certified Kubernetes Security Specialist CKS study guide
Full concept coverage aligned to exam objectives
- →
CKS practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related CKS practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Monitoring Logging and Runtime Security practice questions
Practise CKS questions linked to Monitoring Logging and Runtime Security.
Cluster Setup and Hardening practice questions
Practise CKS questions linked to Cluster Setup and Hardening.
System Hardening practice questions
Practise CKS questions linked to System Hardening.
Minimize Microservice Vulnerabilities practice questions
Practise CKS questions linked to Minimize Microservice Vulnerabilities.
Supply Chain Security practice questions
Practise CKS questions linked to Supply Chain Security.
Monitoring, Logging and Runtime Security practice questions
Practise CKS questions linked to Monitoring, Logging and Runtime Security.
Cluster Setup practice questions
Practise CKS questions linked to Cluster Setup.
Cluster Hardening practice questions
Practise CKS questions linked to Cluster Hardening.
CKS fundamentals practice questions
Practise CKS questions linked to CKS fundamentals.
CKS scenario practice questions
Practise CKS questions linked to CKS scenario.
CKS troubleshooting practice questions
Practise CKS questions linked to CKS troubleshooting.
Practice this exam
Start a free CKS practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
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": msg}] { container := input.review.object.spec.containers[_] not container.securityContext.readOnlyRootFilesystem msg := "readOnlyRootFilesystem must be true" } — Option B is correct because it uses `not container.securityContext.readOnlyRootFilesystem` to trigger a violation when the field is missing, false, or nil. In Rego, `not` succeeds when the expression inside it fails, so this rule denies any pod where any container does not have `readOnlyRootFilesystem` explicitly set to `true`. This matches the requirement to deny pods unless the field is `true`.
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 →
Keep practising
More CKS practice questions
- Which flag is used to restrict the kubelet's ability to modify node status and pods?
- A Falco rule has priority `WARNING` and output: `Sensitive file opened (user=%user.name command=%proc.cmdline file=%fd.n…
- Falco detects a shell being opened inside a container. Which Falco rule field is used to specify the syscall condition f…
- A security audit reveals that a ServiceAccount named 'monitor' has a ClusterRoleBinding to the cluster-admin role. What…
- Match each Kubernetes security component to its description.
- Match each Kubernetes certificate type to its usage.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.