CKS Minimize Microservice Vulnerabilities Practice Question
This CKS practice question tests your understanding of minimize microservice vulnerabilities. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which TWO of the following are valid methods to restrict a container's filesystem to read-only in Kubernetes?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set readOnlyRootFilesystem: true in the container's securityContext
Setting readOnlyRootFilesystem: true in the container securityContext makes the root filesystem read-only. Using an emptyDir volume with readOnly: true mounts an emptyDir as read-only, but the root filesystem remains writable. hostPath is not read-only by default. ConfigMap volumes are typically mounted read-only by default, but the question asks about restricting the container's filesystem. Option A directly makes the root filesystem read-only. Option D also works by mounting a volume read-only, but it does not restrict the root filesystem. However, the question says 'restrict a container's filesystem to read-only' which can include specific mounts. The intended correct answers are A and D. (Note: In many contexts, 'filesystem' refers to the root filesystem, but volumes are also part of the filesystem.)
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Use a ConfigMap volume with defaultMode 0444
Why it's wrong here
ConfigMap volumes are typically read-only, but again not restricting the root filesystem.
✗
Set readOnly: true on a hostPath volume mount
Why it's wrong here
hostPath mounts can be set read-only, but this does not restrict the root filesystem.
✓
Set readOnlyRootFilesystem: true in the container's securityContext
Why this is correct
This makes the container's root filesystem read-only.
Related concept
Static NAT maps one inside address to one outside address.
✓
Mount an emptyDir volume with readOnly: true
Why this is correct
Mounting a volume as read-only restricts writes to that mount point, contributing to a read-only filesystem for that path.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CKS question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CKS NAT questions on configuration and troubleshooting.
Minimize Microservice Vulnerabilities — This question tests Minimize Microservice Vulnerabilities — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Set readOnlyRootFilesystem: true in the container's securityContext — Setting readOnlyRootFilesystem: true in the container securityContext makes the root filesystem read-only. Using an emptyDir volume with readOnly: true mounts an emptyDir as read-only, but the root filesystem remains writable. hostPath is not read-only by default. ConfigMap volumes are typically mounted read-only by default, but the question asks about restricting the container's filesystem. Option A directly makes the root filesystem read-only. Option D also works by mounting a volume read-only, but it does not restrict the root filesystem. However, the question says 'restrict a container's filesystem to read-only' which can include specific mounts. The intended correct answers are A and D. (Note: In many contexts, 'filesystem' refers to the root filesystem, but volumes are also part of the filesystem.)
What should I do if I get this CKS question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CKS NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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