CKAD Practice Question: Application Environment, Configuration and Security
This CKAD practice question tests your understanding of application environment, configuration and security. 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.
What is the effect of setting 'readOnlyRootFilesystem: true' in a container's securityContext?
The container can only read from the root filesystem, but can still write to /tmp.
Why wrong: If /tmp is part of the root filesystem, it is also read-only. To have writable /tmp, it must be a separate volume.
B
The container's root filesystem is mounted as read-only.
Correct. The container will be unable to write to its own filesystem.
C
The container cannot write to any mounted volumes.
Why wrong: It only affects the root filesystem; volumes can still be read-write depending on their mount options.
D
The container will be killed if it attempts to write to the root filesystem.
Why wrong: The write operation will fail with an error, but the container will not be killed. The container may crash if the application cannot handle the error.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The container's root filesystem is mounted as read-only.
Setting `readOnlyRootFilesystem: true` in a container's securityContext mounts the container's root filesystem as read-only. This prevents any process inside the container from writing to the root filesystem, enhancing security by reducing the attack surface and ensuring immutability of the container image layers. It does not affect writable volumes mounted at other paths, such as emptyDir or hostPath volumes.
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.
✗
The container can only read from the root filesystem, but can still write to /tmp.
Why it's wrong here
If /tmp is part of the root filesystem, it is also read-only. To have writable /tmp, it must be a separate volume.
✓
The container's root filesystem is mounted as read-only.
Why this is correct
Correct. The container will be unable to write to its own filesystem.
Related concept
Read the scenario before looking for a memorised answer.
✗
The container cannot write to any mounted volumes.
Why it's wrong here
It only affects the root filesystem; volumes can still be read-write depending on their mount options.
✗
The container will be killed if it attempts to write to the root filesystem.
Why it's wrong here
The write operation will fail with an error, but the container will not be killed. The container may crash if the application cannot handle the error.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'readOnlyRootFilesystem' with making all volumes read-only, or assume the container is terminated on write attempts, when in reality only the root filesystem is affected and writes simply fail silently.
Detailed technical explanation
How to think about this question
Under the hood, this setting modifies the container's mount namespace so that the root filesystem (typically an overlay filesystem combining image layers and a writable layer) is mounted with the MS_RDONLY flag. In Kubernetes, this is enforced by the container runtime (e.g., containerd or CRI-O) via the OCI runtime spec's `readonly` field. A real-world scenario is running a container that only needs to serve static files or execute code without persisting state, reducing the risk of malware writing malicious files to the container image.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CKAD question in full detail.
Application Environment, Configuration and Security — This question tests Application Environment, Configuration and Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The container's root filesystem is mounted as read-only. — Setting `readOnlyRootFilesystem: true` in a container's securityContext mounts the container's root filesystem as read-only. This prevents any process inside the container from writing to the root filesystem, enhancing security by reducing the attack surface and ensuring immutability of the container image layers. It does not affect writable volumes mounted at other paths, such as emptyDir or hostPath volumes.
What should I do if I get this CKAD 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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Question Discussion
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