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XK0-006 Practice Question: Given the Dockerfile in the exhibit, which best…

Exhibit

Refer to the exhibit.

FROM ubuntu:20.04
RUN apt-get update
RUN apt-get install -y python3
COPY app.py /app/
CMD ["python3", "/app/app.py"]

Given the Dockerfile in the exhibit, which best practice is being violated?

⚠ Common exam trap

CompTIA often tests the nuance that separating `apt-get update` and `apt-get install` is a caching and security violation, not just a style issue, and candidates may mistakenly focus on cache cleanup or .dockerignore as the primary problem.

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

✓

Not combining apt-get update and install in one RUN command

The Dockerfile violates the best practice of combining `apt-get update` and `apt-get install` in a single RUN command. When these are separated, Docker caches the layer from `apt-get update`, so subsequent builds may use a stale package index, potentially installing outdated or vulnerable packages. Combining them ensures that the update and install happen atomically, reducing image size and guaranteeing a fresh package index.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • ✓

    Not combining apt-get update and install in one RUN command

    Why this is correct

    Should be combined: RUN apt-get update && apt-get install -y python3

  • ✗

    Using a non-LTS base image

    Why it's wrong here

    20.04 is LTS.

  • ✗

    Not using a .dockerignore file

    Why it's wrong here

    Missing .dockerignore is not a best practice violation for this simple case.

  • ✗

    Running apt-get update without cache cleanup

    Why it's wrong here

    rm -rf /var/lib/apt/lists/* is recommended, but not the primary violation.

About these practice questions

One of 979 original XK0-006 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →

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JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

This XK0-006 practice question is part of Courseiva's free CompTIA 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 XK0-006 exam.