- A
apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: allow-api-to-db namespace: finance spec: podSelector: matchLabels: app: api ingress: - from: - podSelector: matchLabels: app: db ports: - port: 5432
Why wrong: The podSelector selects 'app: api' but should select the target pods 'app: db'.
- B
apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: allow-api-to-db namespace: finance spec: podSelector: matchLabels: app: api egress: - to: - podSelector: matchLabels: app: db ports: - port: 5432
Why wrong: This controls egress from api pods, not ingress to db pods; it also does not deny other traffic to db.
- C
apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: allow-api-to-db namespace: finance spec: podSelector: matchLabels: app: db ingress: - from: - podSelector: matchLabels: app: api
Why wrong: Missing port restriction; allows all ports from api pods.
- D
apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: allow-api-to-db namespace: finance spec: podSelector: matchLabels: app: db ingress: - from: - podSelector: matchLabels: app: api ports: - port: 5432
Correctly targets db pods, allows ingress from api pods on port 5432, and implicitly denies all other ingress.
CKS Cluster Setup and Hardening Practice Question
This CKS practice question tests your understanding of cluster setup and hardening. 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.
After a security incident, you need to restrict which pods can communicate with each other in the 'finance' namespace. You want to allow only pods with label 'app: api' to connect to pods with label 'app: db' on TCP port 5432, and deny all other traffic. Which NetworkPolicy should you create?
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
apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: allow-api-to-db namespace: finance spec: podSelector: matchLabels: app: db ingress: - from: - podSelector: matchLabels: app: api ports: - port: 5432
Option D is correct because it defines a NetworkPolicy that selects pods with label 'app: db' as the target and allows ingress traffic only from pods with label 'app: api' on TCP port 5432. By default, if no NetworkPolicy exists, all traffic is allowed; once a NetworkPolicy selects a pod, all traffic not explicitly allowed is denied. This policy therefore restricts communication to only the intended api-to-db flow on the specified port.
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.
- ✗
apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: allow-api-to-db namespace: finance spec: podSelector: matchLabels: app: api ingress: - from: - podSelector: matchLabels: app: db ports: - port: 5432
Why it's wrong here
The podSelector selects 'app: api' but should select the target pods 'app: db'.
- ✗
apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: allow-api-to-db namespace: finance spec: podSelector: matchLabels: app: api egress: - to: - podSelector: matchLabels: app: db ports: - port: 5432
Why it's wrong here
This controls egress from api pods, not ingress to db pods; it also does not deny other traffic to db.
- ✗
apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: allow-api-to-db namespace: finance spec: podSelector: matchLabels: app: db ingress: - from: - podSelector: matchLabels: app: api
Why it's wrong here
Missing port restriction; allows all ports from api pods.
- ✓
apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: allow-api-to-db namespace: finance spec: podSelector: matchLabels: app: db ingress: - from: - podSelector: matchLabels: app: api ports: - port: 5432
Why this is correct
Correctly targets db pods, allows ingress from api pods on port 5432, and implicitly denies all other ingress.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CNCF often tests the direction of traffic flow: candidates mistakenly apply the policy to the source pod (app: api) with an ingress rule, which would control traffic coming into the api pod rather than traffic going to the db pod, or they forget to specify the port, allowing all ports from the allowed source.
Detailed technical explanation
How to think about this question
NetworkPolicy rules are additive: when a pod is selected by a policy, all traffic not matching an ingress or egress rule is denied by default. The podSelector in spec.podSelector determines which pods the policy applies to, and the ingress.from.podSelector matches source pods. Port restrictions are applied at the transport layer (TCP/UDP/SCTP), and omitting the port field allows all ports. In a zero-trust security model, such policies are critical for micro-segmentation, and misconfiguring the direction (ingress vs egress) or the selector can leave unintended access paths open.
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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Cluster Setup and Hardening — study guide chapter
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FAQ
Questions learners often ask
What does this CKS question test?
Cluster Setup and Hardening — This question tests Cluster Setup and Hardening — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: apiVersion: networking.k8s.io/v1 kind: NetworkPolicy metadata: name: allow-api-to-db namespace: finance spec: podSelector: matchLabels: app: db ingress: - from: - podSelector: matchLabels: app: api ports: - port: 5432 — Option D is correct because it defines a NetworkPolicy that selects pods with label 'app: db' as the target and allows ingress traffic only from pods with label 'app: api' on TCP port 5432. By default, if no NetworkPolicy exists, all traffic is allowed; once a NetworkPolicy selects a pod, all traffic not explicitly allowed is denied. This policy therefore restricts communication to only the intended api-to-db flow on the specified port.
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
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Last reviewed: Jun 30, 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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