- A
Write a MutatingWebhookConfiguration that adds the label automatically.
Why wrong: The requirement is to enforce (deny) namespaces without the label, not mutate them. However, mutating could be an alternative, but not the typical enforcement method.
- B
Use kubectl label command with a --validate flag.
Why wrong: There is no built-in kubectl validation for required labels; policy enforcement requires an admission controller.
- C
Create a ValidatingWebhookConfiguration that directly contains the Rego policy.
Why wrong: ValidatingWebhookConfiguration can call an external webhook, but Gatekeeper uses a custom resource model (ConstraintTemplate and Constraint) to manage policies.
- D
Create a ConstraintTemplate with Rego that denies namespaces missing the label, then create a Constraint referencing that template.
This is the standard Gatekeeper pattern: ConstraintTemplate defines the rule, Constraint applies it to specific resources.
Enforce Namespace Labels with OPA Gatekeeper
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.
A security team wants to use OPA/Gatekeeper to enforce that all namespaces must have a label 'security-tier' with value 'high' or 'medium'. What is the correct approach?
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
Create a ConstraintTemplate with Rego that denies namespaces missing the label, then create a Constraint referencing that template.
Option D is correct because OPA/Gatekeeper enforces policies via a two-part model: a ConstraintTemplate defines the Rego logic (e.g., denying a namespace if it lacks the required label), and a Constraint instantiates that template with specific parameters (e.g., 'security-tier' with values 'high' or 'medium'). This decouples policy definition from enforcement, allowing Gatekeeper's admission webhook to reject non-compliant resources at creation or update time.
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.
- ✗
Write a MutatingWebhookConfiguration that adds the label automatically.
Why it's wrong here
The requirement is to enforce (deny) namespaces without the label, not mutate them. However, mutating could be an alternative, but not the typical enforcement method.
- ✗
Use kubectl label command with a --validate flag.
Why it's wrong here
There is no built-in kubectl validation for required labels; policy enforcement requires an admission controller.
- ✗
Create a ValidatingWebhookConfiguration that directly contains the Rego policy.
Why it's wrong here
ValidatingWebhookConfiguration can call an external webhook, but Gatekeeper uses a custom resource model (ConstraintTemplate and Constraint) to manage policies.
- ✓
Create a ConstraintTemplate with Rego that denies namespaces missing the label, then create a Constraint referencing that template.
Why this is correct
This is the standard Gatekeeper pattern: ConstraintTemplate defines the rule, Constraint applies it to specific resources.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The key distinction in OPA/Gatekeeper is between mutation (MutatingWebhookConfiguration) and validation (ValidatingWebhookConfiguration), and that policies must be defined via ConstraintTemplates and Constraints, not embedded directly in webhook configurations.
Detailed technical explanation
How to think about this question
Under the hood, Gatekeeper registers a ValidatingWebhookConfiguration that intercepts all API server requests matching its rules. When a namespace creation request arrives, Gatekeeper evaluates the Rego policy defined in the ConstraintTemplate; if the namespace lacks the required label, the webhook returns an admission denial with a custom message. A real-world scenario is enforcing PCI-DSS compliance by ensuring all namespaces in a payment processing cluster have a 'compliance-tier' label, preventing accidental deployment into unlabeled environments.
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.
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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: Create a ConstraintTemplate with Rego that denies namespaces missing the label, then create a Constraint referencing that template. — Option D is correct because OPA/Gatekeeper enforces policies via a two-part model: a ConstraintTemplate defines the Rego logic (e.g., denying a namespace if it lacks the required label), and a Constraint instantiates that template with specific parameters (e.g., 'security-tier' with values 'high' or 'medium'). This decouples policy definition from enforcement, allowing Gatekeeper's admission webhook to reject non-compliant resources at creation or update time.
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
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