CKS Monitoring, Logging and Runtime Security Practice Question
This CKS practice question tests your understanding of monitoring, logging and runtime security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 have deployed a pod and set `securityContext.readOnlyRootFilesystem: true`. The pod is failing to start with an error about writing to `/tmp`. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The pod is missing an emptyDir volume mounted at `/tmp`
When `readOnlyRootFilesystem` is true, the container cannot write to any path on the root filesystem unless a writable volume is mounted. `/tmp` is on the root filesystem by default, so the container needs an emptyDir volume mounted at `/tmp` to write there.
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.
✗
The `securityContext` is misspelled
Why it's wrong here
Misspelling would cause a validation error, not a runtime write error.
✓
The pod is missing an emptyDir volume mounted at `/tmp`
Why this is correct
An emptyDir volume provides a writable location on an otherwise read-only root filesystem.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The container image does not have `/tmp` directory
Why it's wrong here
Even if the directory exists, writing to it requires a writable filesystem.
✗
The container is running as a non-root user
Why it's wrong here
Non-root users can still write if the filesystem is writable; the issue is the read-only root filesystem.
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.
Monitoring, Logging and Runtime Security — This question tests Monitoring, Logging and Runtime Security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The pod is missing an emptyDir volume mounted at `/tmp` — When `readOnlyRootFilesystem` is true, the container cannot write to any path on the root filesystem unless a writable volume is mounted. `/tmp` is on the root filesystem by default, so the container needs an emptyDir volume mounted at `/tmp` to write there.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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