200-901 Application Deployment and Security Practice Question
This 200-901 practice question tests your understanding of application deployment 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.
Exhibit
FROM python:3.9-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install -r requirements.txt
COPY . .
EXPOSE 5000
CMD ["python", "app.py"]
Refer to the exhibit. The Docker image built from this Dockerfile is larger than expected. Which optimization should be recommended?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a multi-stage build.
Multi-stage builds allow you to use multiple FROM statements in your Dockerfile. You can compile or install dependencies in an intermediate stage using a full-featured base image, then copy only the necessary artifacts (e.g., compiled code, libraries) into a final, minimal runtime image. This dramatically reduces the final image size by discarding build tools, temporary files, and unnecessary layers from the earlier stages.
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.
✗
Use a smaller base image like python:3.9-alpine.
Why it's wrong here
This is a valid optimization but not the most recommended for this simple case; multi-stage build is more comprehensive.
✗
Combine RUN and COPY layers to reduce layers.
Why it's wrong here
This reduces layers but not the actual size; cache inefficiency may increase build time.
✗
Remove the EXPOSE instruction.
Why it's wrong here
EXPOSE is metadata and does not affect image size.
✓
Use a multi-stage build.
Why this is correct
Multi-stage builds allow copying only necessary artifacts, significantly reducing the final image size.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that reducing the number of layers (Option B) or using a smaller base image (Option A) is the primary way to shrink image size, when in fact multi-stage builds are the correct, targeted solution for removing build-time artifacts that inflate the final image.
Detailed technical explanation
How to think about this question
Under the hood, each Dockerfile instruction creates a new layer that is stored as a diff from the previous layer. In a single-stage build, all intermediate files (e.g., compilers, package manager caches, source code) remain in the final image. Multi-stage builds leverage the fact that only the final stage's layers are saved; intermediate stages are discarded after their artifacts are copied. For example, a Python app built with gcc and system headers can be compiled in a 'builder' stage using python:3.9-slim, then the compiled .so files are copied to a python:3.9-alpine final stage, eliminating hundreds of megabytes of build dependencies.
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 200-901 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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Application Deployment and Security — This question tests Application Deployment and Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a multi-stage build. — Multi-stage builds allow you to use multiple FROM statements in your Dockerfile. You can compile or install dependencies in an intermediate stage using a full-featured base image, then copy only the necessary artifacts (e.g., compiled code, libraries) into a final, minimal runtime image. This dramatically reduces the final image size by discarding build tools, temporary files, and unnecessary layers from the earlier stages.
What should I do if I get this 200-901 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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