This CKS practice question tests your understanding of cluster setup and 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.
A DevOps engineer needs to restrict the outbound network traffic from pods running in namespace 'secure-ns'. Which NetworkPolicy configuration achieves this by default?
Apply a NetworkPolicy that selects pods in 'secure-ns' and has an empty egress section.
An empty egress rule blocks all egress traffic.
B
Apply a NetworkPolicy that selects pods in 'secure-ns' and has an egress rule allowing all traffic.
Why wrong: This allows all egress, not restricting it.
C
No NetworkPolicy is needed because egress is denied by default.
Why wrong: By default, egress is allowed if no NetworkPolicy selects the pod.
D
Apply a NetworkPolicy that selects pods in 'secure-ns' and has an egress rule allowing traffic to port 53.
Why wrong: This only allows DNS traffic, but other egress is blocked. However, the question asks 'which configuration achieves this by default?' and an empty egress is the correct approach.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Apply a NetworkPolicy that selects pods in 'secure-ns' and has an empty egress section.
By default, Kubernetes NetworkPolicies are additive and deny-all unless explicitly allowed. Applying a NetworkPolicy with an empty egress section (no egress rules) to pods in 'secure-ns' effectively denies all outbound traffic from those pods, because the policy's egress field defaults to an empty list, which matches no traffic. This is the standard Kubernetes behavior for restricting egress.
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.
✓
Apply a NetworkPolicy that selects pods in 'secure-ns' and has an empty egress section.
Why this is correct
An empty egress rule blocks all egress traffic.
Related concept
Read the scenario before looking for a memorised answer.
✗
Apply a NetworkPolicy that selects pods in 'secure-ns' and has an egress rule allowing all traffic.
Why it's wrong here
This allows all egress, not restricting it.
✗
No NetworkPolicy is needed because egress is denied by default.
Why it's wrong here
By default, egress is allowed if no NetworkPolicy selects the pod.
✗
Apply a NetworkPolicy that selects pods in 'secure-ns' and has an egress rule allowing traffic to port 53.
Why it's wrong here
This only allows DNS traffic, but other egress is blocked. However, the question asks 'which configuration achieves this by default?' and an empty egress is the correct approach.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume egress is denied by default (Option C), but Kubernetes allows all egress until a NetworkPolicy explicitly restricts it, and an empty egress section in a policy is the correct way to achieve a deny-all for outbound traffic.
Detailed technical explanation
How to think about this question
When a NetworkPolicy selects a pod, it isolates that pod's traffic; any traffic not explicitly allowed by the policy is denied. An empty egress section means the policy has no egress rules, so no outbound traffic is permitted. This behavior is defined in the Kubernetes NetworkPolicy spec (networking.k8s.io/v1), where an empty `egress` array is equivalent to a deny-all for egress. In practice, this is often used to enforce a zero-trust model for pod egress, requiring explicit allow rules for any outbound communication.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CKS question in full detail.
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: Apply a NetworkPolicy that selects pods in 'secure-ns' and has an empty egress section. — By default, Kubernetes NetworkPolicies are additive and deny-all unless explicitly allowed. Applying a NetworkPolicy with an empty egress section (no egress rules) to pods in 'secure-ns' effectively denies all outbound traffic from those pods, because the policy's egress field defaults to an empty list, which matches no traffic. This is the standard Kubernetes behavior for restricting egress.
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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