200-901 Application Deployment and Security Practice Question
A developer is writing a Dockerfile for a Node.js application. Which TWO instructions are commonly used to define the command that runs when the container starts?
⚠ Common exam trap
Cisco often tests the distinction between build-time instructions (RUN) and runtime instructions (CMD/ENTRYPOINT), and the trap here is that candidates confuse RUN (which executes during `docker build`) with CMD (which executes during `docker run`).
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
✓
CMD
The CMD instruction in a Dockerfile provides default arguments for the container's entrypoint or defines the command to execute when the container starts. For a Node.js application, CMD is commonly used to specify the startup command, such as `CMD ["node", "app.js"]`, which runs the Node.js process. This instruction can be overridden at runtime by providing a command after `docker run`.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
CMD
Why this is correct
CMD specifies the command to run when the container starts.
- ✗
RUN
Why it's wrong here
RUN executes commands during build, not at container start.
- ✗
START
Why it's wrong here
START is not a valid Dockerfile instruction.
- ✓
ENTRYPOINT
Why this is correct
ENTRYPOINT also specifies the startup command, often used with CMD for arguments.
- ✗
EXPOSE
Why it's wrong here
EXPOSE documents ports, but does not run any command.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.