This KCNA practice question tests your understanding of container orchestration. 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 statements about container images are correct? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Each layer is identified by a unique hash
Option B is correct because each layer in a container image is identified by a unique content-addressable hash (typically a SHA-256 digest). This hash is computed from the layer's contents and metadata, ensuring integrity and enabling layer caching and deduplication across images. The hash is used in the image manifest (as defined by the OCI Image Specification) to reference each layer uniquely.
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.
✗
Images are always pulled from a private registry
Why it's wrong here
Images can be pulled from public registries like Docker Hub.
✓
Each layer is identified by a unique hash
Why this is correct
Layers are content-addressable and identified by their digest.
Related concept
Read the scenario before looking for a memorised answer.
✗
Images can be modified at runtime by writing to the container layer
Why it's wrong here
At runtime, the container has a writable layer, but the image itself is immutable.
✓
Images are built from a series of read-only layers
Why this is correct
Images are composed of layers that are stacked.
Related concept
Read the scenario before looking for a memorised answer.
✗
Images are stored on the host filesystem after being pulled
Why it's wrong here
Images are stored in the local image cache, but this is not a defining statement; they are also stored in registries.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CNCF often tests the misconception that images are stored directly on the host filesystem like regular files, when in reality they are stored in a runtime-managed cache (e.g., /var/lib/docker) and are not directly accessible as ordinary files.
Detailed technical explanation
How to think about this question
Under the hood, container images are composed of a stack of read-only layers, each represented by a tar archive and identified by a SHA-256 digest in the image manifest (OCI Image Spec v1.0). When a container runs, a thin writable layer (the container layer) is added on top using a union filesystem like OverlayFS, which uses copy-on-write to allow modifications without altering the underlying image layers. This layering mechanism enables efficient storage and sharing of common base layers across multiple containers.
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 practitioner preparing for the KCNA exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this KCNA question in full detail.
Container Orchestration — This question tests Container Orchestration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Each layer is identified by a unique hash — Option B is correct because each layer in a container image is identified by a unique content-addressable hash (typically a SHA-256 digest). This hash is computed from the layer's contents and metadata, ensuring integrity and enabling layer caching and deduplication across images. The hash is used in the image manifest (as defined by the OCI Image Specification) to reference each layer uniquely.
What should I do if I get this KCNA 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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