- A
Use the ADD instruction instead of COPY to copy local files into the image.
Why wrong: COPY is preferred over ADD for local files because ADD has additional features (like tar extraction) that can be unexpected.
- B
Combine multiple RUN commands into a single RUN statement to reduce image layers.
Why wrong: While reducing layers can be beneficial, combining commands into one RUN is not always best; it can reduce cacheability. The recommended practice is to minimize layers but not at the expense of readability.
- C
Use a .dockerignore file to exclude unnecessary files from the build context.
.dockerignore reduces build context size and improves security by excluding sensitive files.
- D
Use the EXPOSE instruction to secure the container by limiting exposed ports.
Why wrong: EXPOSE is documentation only; it does not actually open or secure ports. Security is achieved via -p flag or network policies.
- E
Prefer official base images from trusted registries.
Official images are maintained and scanned for vulnerabilities, reducing security risks.
Quick Answer
The correct answer is that you should prefer official base images from trusted registries, as this ensures a secure, stable foundation for your containerized applications. This is a core Dockerfile best practice because official images are maintained by the software vendor or the Docker team, receive regular security patches, and are verified to be free of malware, reducing your attack surface significantly. On the Cisco DevNet Associate 200-901 exam, this concept tests your understanding of secure software supply chains and efficient image layering, often appearing alongside questions about minimizing build context with a .dockerignore file—a common trap is forgetting that a .dockerignore prevents sensitive files like .git or logs from reaching the daemon, which also speeds up builds. To remember this, think of the mnemonic “O-F-F” for Official, From trusted, and Filter with .dockerignore.
200-901 Application Deployment and Security Practice Question
This 200-901 practice question tests your understanding of application deployment and security. 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.
Which TWO statements about Dockerfile best practices are correct? (Choose two.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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
Use a .dockerignore file to exclude unnecessary files from the build context.
Option C is correct because a .dockerignore file prevents unnecessary files (e.g., node_modules, .git, logs) from being sent to the Docker daemon as part of the build context. This reduces build time, minimizes the risk of including sensitive data, and ensures a cleaner, more efficient image build.
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.
- ✗
Use the ADD instruction instead of COPY to copy local files into the image.
Why it's wrong here
COPY is preferred over ADD for local files because ADD has additional features (like tar extraction) that can be unexpected.
- ✗
Combine multiple RUN commands into a single RUN statement to reduce image layers.
Why it's wrong here
While reducing layers can be beneficial, combining commands into one RUN is not always best; it can reduce cacheability. The recommended practice is to minimize layers but not at the expense of readability.
- ✓
Use a .dockerignore file to exclude unnecessary files from the build context.
Why this is correct
.dockerignore reduces build context size and improves security by excluding sensitive files.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use the EXPOSE instruction to secure the container by limiting exposed ports.
Why it's wrong here
EXPOSE is documentation only; it does not actually open or secure ports. Security is achieved via -p flag or network policies.
- ✓
Prefer official base images from trusted registries.
Why this is correct
Official images are maintained and scanned for vulnerabilities, reducing security risks.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that EXPOSE actually secures or opens ports, when in reality it is only documentation and has no effect on container network security.
Trap categories for this question
Command / output trap
While reducing layers can be beneficial, combining commands into one RUN is not always best; it can reduce cacheability. The recommended practice is to minimize layers but not at the expense of readability.
Detailed technical explanation
How to think about this question
The Docker build context is the entire directory sent to the Docker daemon; a .dockerignore file uses glob patterns to exclude files, similar to .gitignore, and can significantly speed up builds on large projects. The COPY vs ADD distinction is codified in the Dockerfile reference: ADD has extra features like automatic tar extraction and URL fetching, which can lead to unexpected results if not intended. The EXPOSE instruction does not affect network security—it is metadata that can be read by tools like docker ps or used by container orchestration platforms to map ports automatically.
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
Learn the concepts, then practise the questions
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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: Use a .dockerignore file to exclude unnecessary files from the build context. — Option C is correct because a .dockerignore file prevents unnecessary files (e.g., node_modules, .git, logs) from being sent to the Docker daemon as part of the build context. This reduces build time, minimizes the risk of including sensitive data, and ensures a cleaner, more efficient image build.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
2 more ways this is tested on 200-901
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Refer to the exhibit. A developer is building a Docker image for a Node.js application. The Dockerfile contains: ``` FROM node:14 WORKDIR /usr/src/app COPY package*.json ./ RUN npm install COPY . . CMD ["node", "app.js"] ``` When building, the error shown occurs. What is the most likely cause?
hard- A.The Dockerfile should use the root user for running npm install.
- B.The npm install command should be run with the --unsafe-perm flag.
- C.The base image node:14 is outdated and contains a bug.
- ✓ D.The application is running as a non-root user (e.g., node) that lacks write permission to the working directory.
Why D: The error occurs because the official Node.js Docker image (node:14) runs as a non-root user named 'node' by default. The WORKDIR /usr/src/app is owned by root, so the 'node' user lacks write permission to that directory. When npm install tries to create node_modules or write package-lock.json, it fails with a permission error. Option D correctly identifies this user-permission mismatch.
Variation 2. A developer wants to ensure that a Docker container running a web application can only accept incoming traffic on port 443. Which Docker run option should be used?
easy- A.docker run --port 443 myapp
- B.docker run --net host myapp
- ✓ C.docker run -p 443:443 myapp
- D.docker run --expose 443 myapp
Why C: Option C is correct because the `-p 443:443` flag publishes container port 443 to the host port 443, mapping incoming traffic on the host's port 443 to the container's port 443. This ensures the web application inside the container only accepts incoming traffic on port 443, as the host firewall and Docker's port mapping restrict access to that specific port.
Last reviewed: Jun 11, 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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