PCD Building and testing applications Practice Question
This PCD practice question tests your understanding of building and testing applications. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Network Topology
Refer to the exhibit. A developer writes the above Dockerfile for a Cloud Run service. The service fails to start. The logs indicate that the container exited immediately. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Clue: "immediately / without restart"
Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
The WORKDIR is set to a directory that doesn't exist
Why wrong: WORKDIR creates the directory if it doesn't exist; this is not the cause.
B
The server.js file is missing from the build context
If server.js is not copied into the image (e.g., it's in a different directory or excluded by .dockerignore), the container has no entrypoint and exits immediately.
C
The CMD instruction is incorrectly formatted
Why wrong: The CMD is correctly written as JSON array; this is not the issue.
D
The EXPOSE 8080 instruction is unnecessary and may cause conflicts
Why wrong: EXPOSE is just documentation; it does not affect container startup.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The server.js file is missing from the build context
The most likely cause is that the server.js file is missing from the build context. When the Dockerfile contains a COPY command (e.g., COPY . .) to copy application files, the server.js file must exist in the source directory from which the build is run. If it is absent, the container will have no entry point, and the CMD instruction (e.g., CMD ["node", "server.js"]) will fail because the file does not exist inside the image, causing the container to exit immediately. Cloud Run requires the container to start a listening process; without server.js, no process runs.
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.
✗
The WORKDIR is set to a directory that doesn't exist
Why it's wrong here
WORKDIR creates the directory if it doesn't exist; this is not the cause.
✓
The server.js file is missing from the build context
Why this is correct
If server.js is not copied into the image (e.g., it's in a different directory or excluded by .dockerignore), the container has no entrypoint and exits immediately.
Clue confirmation
The clue words "most likely", "immediately / without restart" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The CMD instruction is incorrectly formatted
Why it's wrong here
The CMD is correctly written as JSON array; this is not the issue.
✗
The EXPOSE 8080 instruction is unnecessary and may cause conflicts
Why it's wrong here
EXPOSE is just documentation; it does not affect container startup.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a missing WORKDIR or an incorrect CMD format is the root cause, but the real issue is that the application file (server.js) is not copied into the image, leading to an immediate container exit.
Detailed technical explanation
How to think about this question
The COPY instruction in a Dockerfile copies files from the build context (the directory specified in the docker build command) into the image. If server.js is not present in that context, the COPY operation either fails (if explicitly listed) or silently omits it (if using a wildcard), resulting in an image without the required entry point. Cloud Run injects the PORT environment variable (default 8080), but the container must still have a running process; without server.js, Node.js cannot execute the CMD, and the container exits with code 0 or 1. This is a common issue when developers forget to include all source files in the build context or misconfigure .dockerignore.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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.
Building and testing applications — This question tests Building and testing applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The server.js file is missing from the build context — The most likely cause is that the server.js file is missing from the build context. When the Dockerfile contains a COPY command (e.g., COPY . .) to copy application files, the server.js file must exist in the source directory from which the build is run. If it is absent, the container will have no entry point, and the CMD instruction (e.g., CMD ["node", "server.js"]) will fail because the file does not exist inside the image, causing the container to exit immediately. Cloud Run requires the container to start a listening process; without server.js, no process runs.
What should I do if I get this PCD 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: "most likely", "immediately / without restart". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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