- A
Enable Pod Security Admission with the 'baseline' policy in enforce mode for acme-corp namespace, and add a mutating webhook to set readOnlyRootFilesystem
Why wrong: Baseline does not enforce readOnlyRootFilesystem; mutating webhook adds complexity.
- B
Use OPA/Gatekeeper to create a ConstraintTemplate that requires readOnlyRootFilesystem and allows only NET_BIND_SERVICE capability, then apply it to acme-corp namespace
OPA can enforce both requirements flexibly.
- C
Use Pod Security Admission with the 'privileged' policy and rely on the legacy container's securityContext
Why wrong: Privileged policy allows everything, defeating security.
- D
Create a new PSP that allows NET_BIND_SERVICE and requires readOnlyRootFilesystem, then bind it to the acme-corp namespace via RoleBinding
Why wrong: PSP is deprecated and not recommended for new deployments.
CKS Cluster Hardening Practice Question
This CKS practice question tests your understanding of cluster hardening. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 the security engineer for a multi-tenant Kubernetes cluster. The cluster uses kubeadm and runs Kubernetes v1.24. Each tenant has a dedicated namespace. A new tenant, 'acme-corp', requires that all pods in their namespace run with a read-only root filesystem and must not be able to escalate privileges. They also need to run a legacy container that must listen on a port below 1024. The cluster currently uses PodSecurityPolicy (PSP) but is planning to migrate to Pod Security Admission (PSA). The legacy container needs to run as non-root with the NET_BIND_SERVICE capability to bind to port 80. You need to configure security policies for the 'acme-corp' namespace without affecting other tenants. Which approach best meets these requirements while following Kubernetes best practices?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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
Use OPA/Gatekeeper to create a ConstraintTemplate that requires readOnlyRootFilesystem and allows only NET_BIND_SERVICE capability, then apply it to acme-corp namespace
Option B is correct because OPA/Gatekeeper allows fine-grained, namespace-scoped policy enforcement that can require readOnlyRootFilesystem and restrict capabilities to only NET_BIND_SERVICE, meeting all requirements without affecting other tenants. Pod Security Admission (PSA) does not support custom capability restrictions or readOnlyRootFilesystem enforcement natively, and PSP is deprecated in Kubernetes v1.24 and being removed, making it unsuitable for new configurations. Gatekeeper’s ConstraintTemplate provides the flexibility to enforce these specific security contexts while following best practices for policy-as-code.
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.
- ✗
Enable Pod Security Admission with the 'baseline' policy in enforce mode for acme-corp namespace, and add a mutating webhook to set readOnlyRootFilesystem
Why it's wrong here
Baseline does not enforce readOnlyRootFilesystem; mutating webhook adds complexity.
- ✓
Use OPA/Gatekeeper to create a ConstraintTemplate that requires readOnlyRootFilesystem and allows only NET_BIND_SERVICE capability, then apply it to acme-corp namespace
Why this is correct
OPA can enforce both requirements flexibly.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use Pod Security Admission with the 'privileged' policy and rely on the legacy container's securityContext
Why it's wrong here
Privileged policy allows everything, defeating security.
- ✗
Create a new PSP that allows NET_BIND_SERVICE and requires readOnlyRootFilesystem, then bind it to the acme-corp namespace via RoleBinding
Why it's wrong here
PSP is deprecated and not recommended for new deployments.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may choose Pod Security Admission (PSA) because it is the newer, recommended replacement for PSP, but PSA lacks the granularity to enforce readOnlyRootFilesystem or restrict capabilities to a single capability like NET_BIND_SERVICE, leading to an incorrect choice like Option A or C.
Detailed technical explanation
How to think about this question
OPA/Gatekeeper uses ConstraintTemplates defined in Rego to enforce custom policies; for this scenario, you would create a template that checks securityContext.readOnlyRootFilesystem: true and securityContext.capabilities.drop: ['ALL'] with add: ['NET_BIND_SERVICE'], ensuring the legacy container can bind to port 80 as non-root. The NET_BIND_SERVICE capability (Linux capability CAP_NET_BIND_SERVICE) allows binding to ports below 1024 without root, which is critical for legacy containers that cannot run as root. In a multi-tenant cluster, namespace-scoped constraints via Gatekeeper avoid impacting other tenants, unlike cluster-wide PSPs or PSA policies that apply to all namespaces unless explicitly excluded.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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.
- →
Cluster Hardening — study guide chapter
Learn the concepts, then practise the questions
- →
Cluster Hardening practice questions
Targeted practice on this topic area only
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Certified Kubernetes Security Specialist CKS study guide
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FAQ
Questions learners often ask
What does this CKS question test?
Cluster Hardening — This question tests Cluster Hardening — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use OPA/Gatekeeper to create a ConstraintTemplate that requires readOnlyRootFilesystem and allows only NET_BIND_SERVICE capability, then apply it to acme-corp namespace — Option B is correct because OPA/Gatekeeper allows fine-grained, namespace-scoped policy enforcement that can require readOnlyRootFilesystem and restrict capabilities to only NET_BIND_SERVICE, meeting all requirements without affecting other tenants. Pod Security Admission (PSA) does not support custom capability restrictions or readOnlyRootFilesystem enforcement natively, and PSP is deprecated in Kubernetes v1.24 and being removed, making it unsuitable for new configurations. Gatekeeper’s ConstraintTemplate provides the flexibility to enforce these specific security contexts while following best practices for policy-as-code.
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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 11, 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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