The answer is that the application is hardcoded to listen on port 8080 instead of dynamically reading the PORT environment variable. Cloud Run injects the PORT environment variable into the container at runtime, and the container must bind to whatever port this variable specifies—even if it defaults to 8080, the application must read process.env.PORT rather than assuming a fixed value. This is a classic trap on the Google Professional Cloud Developer exam: candidates often verify local behavior with docker run -p 8080:8080, which works because the host port mapping matches the hardcoded port, but Cloud Run’s runtime environment may set PORT to a different value (e.g., 8081) for internal routing, causing the container to fail when it tries to bind to the wrong port. The key insight is that EXPOSE in the Dockerfile is documentation only and does not override the runtime PORT variable. Memory tip: always use `process.env.PORT || 8080` in your Node.js app to gracefully fall back while respecting Cloud Run’s dynamic port assignment.
PCD Deploying applications Practice Question
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.
You are deploying a Node.js application on Cloud Run. The container image is stored in Artifact Registry. After deploying with gcloud run deploy, the revision fails with 'Container failed to start. Failed to start and then listen on the port defined by the PORT environment variable.' The application listens on port 8080 by default. The Dockerfile uses EXPOSE 8080. The Cloud Run service is configured with container port 8080. You have verified that the container starts locally using docker run -p 8080:8080. What is the most likely cause of the startup failure?
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 is hardcoded to listen on port 8080 but the Cloud Run environment variable PORT may override it to a different value.
Option A is correct because Cloud Run sets the PORT environment variable to 8080 by default, but if the application is hardcoded to listen on 8080 instead of reading PORT, it may fail if the variable is not set or incorrect. Option B is wrong because the DEFAULT port variable is not used. Option C is wrong because the container port is set correctly. Option D is wrong because port 8080 is not privileged.
Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
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 application is hardcoded to listen on port 8080 but the Cloud Run environment variable PORT may override it to a different value.
Why this is correct
Cloud Run sets the PORT variable; the app must read it.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Authentication checks who the user is.
✗
The application is trying to bind to a privileged port.
Why it's wrong here
Port 8080 is not privileged.
✗
The Cloud Run service is configured with container port 443 by default.
Why it's wrong here
The port is explicitly set to 8080.
✗
The container does not have a proper HEALTHCHECK instruction.
Why it's wrong here
Healthcheck is not required for startup.
Common exam traps
Common exam trap: authentication is not authorization
Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.
Detailed technical explanation
How to think about this question
This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.
KKey Concepts to Remember
Authentication checks who the user is.
Authorization controls what the user is allowed to do after login.
Privilege levels affect access to EXEC and configuration commands.
AAA, TACACS+ and RADIUS can separate login success from command access.
TExam Day Tips
→Do not assume successful login means full administrative access.
→Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
→Separate login problems from permission problems before choosing the answer.
Key takeaway
Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
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. Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access. 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.
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related PCD questions on access control and AAA configuration.
Deploying applications — This question tests Deploying applications — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: The application is hardcoded to listen on port 8080 but the Cloud Run environment variable PORT may override it to a different value. — Option A is correct because Cloud Run sets the PORT environment variable to 8080 by default, but if the application is hardcoded to listen on 8080 instead of reading PORT, it may fail if the variable is not set or incorrect. Option B is wrong because the DEFAULT port variable is not used. Option C is wrong because the container port is set correctly. Option D is wrong because port 8080 is not privileged.
What should I do if I get this PCD question wrong?
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related PCD questions on access control and AAA configuration.
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?
Authentication checks who the user is.
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