- A
RUN export NODE_ENV=production
Why wrong: Incorrect. RUN export does not persist across layers.
- B
ARG NODE_ENV=production
Why wrong: Incorrect. ARG is for build-time variables, not persisted in the final image.
- C
ENV NODE_ENV=production
Correct. ENV sets environment variables that persist in the container.
- D
CMD NODE_ENV=production
Why wrong: Incorrect. CMD sets the command, not environment variables.
Question 542 of 1,000
200-901 Application Deployment and Security Practice Question
This 200-901 practice question tests your understanding of application deployment and security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 for a Node.js application. The application uses environment variables for configuration. Which Dockerfile instruction should be used to set a default value for the NODE_ENV variable?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ENV NODE_ENV=production
Option C is correct because the ENV instruction sets environment variables that persist in the container at runtime, making it the appropriate way to define a default value for NODE_ENV that can be overridden later with `docker run -e`. Unlike shell-level exports or build-time-only ARGs, ENV ensures the variable is available to the Node.js process 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
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
RUN export NODE_ENV=production
Why it's wrong here
Incorrect. RUN export does not persist across layers.
- ✗
ARG NODE_ENV=production
Why it's wrong here
Incorrect. ARG is for build-time variables, not persisted in the final image.
- ✓
ENV NODE_ENV=production
Why this is correct
Correct. ENV sets environment variables that persist in the container.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
CMD NODE_ENV=production
Why it's wrong here
Incorrect. CMD sets the command, not environment variables.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between build-time (ARG) and runtime (ENV) instructions, and the trap here is that candidates confuse ARG with ENV because both can set default values, but only ENV persists into the running container.
Trap categories for this question
Command / output trap
Incorrect. CMD sets the command, not environment variables.
Detailed technical explanation
How to think about this question
The ENV instruction writes the key-value pair into the image's metadata (specifically the `/proc/1/environ` of the container), making it accessible to all child processes. A subtle behavior is that ENV values are also available during subsequent build steps (unlike ARG), which can lead to unintended side effects if a build step depends on a variable that should only be set at runtime. In real-world scenarios, using ENV for NODE_ENV ensures that Node.js frameworks like Express automatically enable production optimizations (e.g., caching views, suppressing stack traces) unless overridden.
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.
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Application Deployment and Security — study guide chapter
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FAQ
Questions learners often ask
What does this 200-901 question test?
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: ENV NODE_ENV=production — Option C is correct because the ENV instruction sets environment variables that persist in the container at runtime, making it the appropriate way to define a default value for NODE_ENV that can be overridden later with `docker run -e`. Unlike shell-level exports or build-time-only ARGs, ENV ensures the variable is available to the Node.js process when the container starts.
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.
About these practice questions
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Last reviewed: Jul 4, 2026
This 200-901 practice question is part of Courseiva's free Cisco 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 200-901 exam.
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