200-901 Application Deployment and Security Practice Question
A developer is writing a Dockerfile for a Node.js application. They want to set a build-time variable for the application version that can be changed without modifying the Dockerfile. Which instruction should be used?
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
✓
ARG
ARG allows passing build-time variables. ENV sets environment variables that persist in the container. CMD and RUN are not for variable definition.
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
Why it's wrong here
RUN executes commands, not for variable definition.
- ✓
ARG
Why this is correct
ARG defines build-time variables that can be overridden.
- ✗
ENV
Why it's wrong here
ENV sets environment variables available at runtime, not build-time adjustable.
- ✗
CMD
Why it's wrong here
CMD sets default command, not variables.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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