This CKAD practice question tests your understanding of application design and build. 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.
A developer is writing a Dockerfile and wants to ensure that the container runs a Python script named 'app.py' as its main process. Which instruction should be used?
EXPOSE 8080
Why wrong: EXPOSE documents a port, it does not run a process.
CMD ["python", "app.py"]
Why wrong: CMD provides default arguments that can be overridden.
ENTRYPOINT ["python", "app.py"]
ENTRYPOINT sets the main command to run python app.py.
RUN ["python", "app.py"]
Why wrong: RUN executes a command during build, not at container start.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
ENTRYPOINT ["python", "app.py"]
ENTRYPOINT sets the main command that will always be executed when the container starts.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
EXPOSE 8080
Why it's wrong here
EXPOSE documents a port, it does not run a process.
CMD ["python", "app.py"]
Why it's wrong here
CMD provides default arguments that can be overridden.
ENTRYPOINT ["python", "app.py"]
Why this is correct
ENTRYPOINT sets the main command to run python app.py.
Related concept
Read the scenario before looking for a memorised answer.
RUN ["python", "app.py"]
Why it's wrong here
RUN executes a command during build, not at container start.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
RUN executes a command during build, not at container start.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the CKAD 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
Identify which CKAD exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Application Design and Build — This question tests Application Design and Build — Read the scenario before looking for a memorised answer..
The correct answer is: ENTRYPOINT ["python", "app.py"] — ENTRYPOINT sets the main command that will always be executed when the container starts.
Identify which CKAD exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 21, 2026
This CKAD practice question is part of Courseiva's free CNCF certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CKAD exam.
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