- A
A ConfigMap containing the Rego policy, then reference it in a custom admission controller
Why wrong: Gatekeeper does not use ConfigMaps for Rego policies; it uses ConstraintTemplate custom resources.
- B
A ConstraintTemplate containing a Rego policy that checks for readOnlyRootFilesystem: true
ConstraintTemplate defines the Rego policy logic and parameters. It must be created before instantiating a Constraint.
- C
A Constraint resource that enforces the readOnlyRootFilesystem rule
Why wrong: The Constraint references a ConstraintTemplate; the template must exist first.
- D
A ValidatingWebhookConfiguration that points to the Gatekeeper service
Why wrong: While Gatekeeper uses a ValidatingWebhookConfiguration, the first step is to define the policy logic in a ConstraintTemplate.
First Resource to Create for OPA 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 need to enforce that all pods in the 'production' namespace run with read-only root filesystems. Which OPA Gatekeeper resource do you create first?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"first"Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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
A ConstraintTemplate containing a Rego policy that checks for readOnlyRootFilesystem: true
Option B is correct because OPA Gatekeeper requires a ConstraintTemplate first to define the Rego policy logic that checks for `readOnlyRootFilesystem: true`. The ConstraintTemplate is a custom resource that tells Gatekeeper what rule to enforce; without it, you cannot create a Constraint to apply the policy to the 'production' namespace. This follows the Gatekeeper workflow: template → constraint → enforcement via admission webhooks.
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.
- ✗
A ConfigMap containing the Rego policy, then reference it in a custom admission controller
Why it's wrong here
Gatekeeper does not use ConfigMaps for Rego policies; it uses ConstraintTemplate custom resources.
- ✓
A ConstraintTemplate containing a Rego policy that checks for readOnlyRootFilesystem: true
Why this is correct
ConstraintTemplate defines the Rego policy logic and parameters. It must be created before instantiating a Constraint.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
A Constraint resource that enforces the readOnlyRootFilesystem rule
Why it's wrong here
The Constraint references a ConstraintTemplate; the template must exist first.
- ✗
A ValidatingWebhookConfiguration that points to the Gatekeeper service
Why it's wrong here
While Gatekeeper uses a ValidatingWebhookConfiguration, the first step is to define the policy logic in a ConstraintTemplate.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The exam often tests the order of Gatekeeper resources: candidates mistakenly think a Constraint (option C) is created first, but the ConstraintTemplate must exist first to define the Rego logic, as the Constraint only applies the rule.
Detailed technical explanation
How to think about this question
Under the hood, Gatekeeper acts as an admission webhook that intercepts API requests and evaluates them against Rego policies defined in ConstraintTemplates. The ConstraintTemplate compiles the Rego into a custom resource definition (CRD), and each Constraint creates an instance of that CRD with parameters (e.g., `namespaces: ["production"]`). A subtle behavior is that if the ConstraintTemplate is not installed first, the Constraint creation will fail because the CRD doesn't exist yet. In a real-world scenario, you might also need to exempt certain system pods (e.g., those in kube-system) by adding `excludedNamespaces` in the Constraint.
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.
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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: A ConstraintTemplate containing a Rego policy that checks for readOnlyRootFilesystem: true — Option B is correct because OPA Gatekeeper requires a ConstraintTemplate first to define the Rego policy logic that checks for `readOnlyRootFilesystem: true`. The ConstraintTemplate is a custom resource that tells Gatekeeper what rule to enforce; without it, you cannot create a Constraint to apply the policy to the 'production' namespace. This follows the Gatekeeper workflow: template → constraint → enforcement via admission webhooks.
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.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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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