This PCD practice question tests your understanding of deploying 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.
A developer is troubleshooting a deployment on Cloud Run. The service fails with 'Container failed to start' error. The container image is built from a Dockerfile that uses CMD ['npm', 'start']. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The application does not listen on the port specified by the PORT environment variable.
Cloud Run requires the containerized application to listen on the port specified by the PORT environment variable (default 8080). If the application is hardcoded to listen on a different port (e.g., 3000) or does not read the PORT variable, Cloud Run's health checks and routing will fail, resulting in a 'Container failed to start' error. The CMD instruction is correct for starting npm, but the application must bind to the correct port.
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 Dockerfile uses CMD instead of ENTRYPOINT.
Why it's wrong here
Both are acceptable; CMD is fine when used with ENTRYPOINT or alone.
✗
The container image is too large and exceeds the memory limit.
Why it's wrong here
This would cause a different error or timeout, not a container start failure.
✓
The application does not listen on the port specified by the PORT environment variable.
Why this is correct
Cloud Run expects the container to listen on the port defined by the PORT env var (default 8080). If the app listens on another port, it fails.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The Cloud Run service does not have permission to pull the image from Container Registry.
Why it's wrong here
That would cause an image pull error, not a container start failure.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that CMD vs ENTRYPOINT is the root cause of container startup failures, when in reality the PORT environment variable mismatch is a far more frequent issue on Cloud Run.
Detailed technical explanation
How to think about this question
Cloud Run injects the PORT environment variable (typically '8080') into the container at runtime. The application must read this variable (e.g., process.env.PORT in Node.js) and bind its HTTP server to that port. If the application listens on a hardcoded port like 3000, Cloud Run's health checks (sent to the PORT) will fail, causing the container to be terminated and retried until the startup deadline (4 minutes by default) expires. This is a common pitfall when migrating from local development or traditional hosting where port 3000 is standard.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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.
Deploying applications — This question tests Deploying applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The application does not listen on the port specified by the PORT environment variable. — Cloud Run requires the containerized application to listen on the port specified by the PORT environment variable (default 8080). If the application is hardcoded to listen on a different port (e.g., 3000) or does not read the PORT variable, Cloud Run's health checks and routing will fail, resulting in a 'Container failed to start' error. The CMD instruction is correct for starting npm, but the application must bind to the correct port.
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". 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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