This CV0-004 practice question tests your understanding of operations and support. 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.
Exhibit
Refer to the exhibit.
```
$ gcloud compute instances list
NAME ZONE MACHINE_TYPE PREEMPTIBLE STATUS
web-server us-east1-b e2-medium true RUNNING
db-server us-east1-b e2-standard-2 STOPPED
$ gcloud compute instances describe web-server --format='get(status,serviceAccounts.email)'
status: RUNNING
serviceAccounts.email: default@project.iam.gserviceaccount.com
$ gcloud compute instances get-serial-port-output web-server
...
[ 10.123456] cloud-init: User data script started
[ 10.654321] cloud-init: ERROR: Failed to fetch metadata from metadata server
...
```
A cloud engineer is troubleshooting a web application that is not responding. The engineer examines the serial console output of the web-server instance and finds the error shown in the exhibit. What is the MOST likely cause of this issue?
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
✓
A firewall rule is blocking traffic to the metadata server IP address 169.254.169.254.
The error shown in the serial console output indicates that the instance cannot reach the metadata server at 169.254.169.254. This IP address is a link-local address used by cloud providers (e.g., AWS, GCP, Azure) to serve instance metadata, including user data scripts. If a firewall rule blocks traffic to this IP, the instance cannot retrieve its user data, causing the web application to fail to start or respond.
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 service account associated with the instance is missing the required permissions.
Why it's wrong here
Missing permissions would cause API call failures, not metadata fetch errors.
✗
The instance is in a STOPPED state and cannot execute user data scripts.
Why it's wrong here
The serial output shows the instance is RUNNING.
✗
The instance does not have a public IP address assigned.
Why it's wrong here
Metadata server is accessible regardless of public IP; it's a link-local address.
✓
A firewall rule is blocking traffic to the metadata server IP address 169.254.169.254.
Why this is correct
The metadata server is accessed via link-local address; blocking this traffic prevents metadata retrieval.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often associate connectivity issues with public IPs or firewall rules blocking external traffic, but the metadata server is an internal link-local address, so the firewall rule must be blocking internal traffic to 169.254.169.254 specifically.
Trap categories for this question
Command / output trap
The serial output shows the instance is RUNNING.
Detailed technical explanation
How to think about this question
The metadata server at 169.254.169.254 is a link-local address (RFC 3927) that cloud hypervisors route internally without traversing a physical network. User data scripts are executed by cloud-init, which queries this IP on boot; if a firewall rule (e.g., iptables or security group) blocks outbound traffic to 169.254.169.254 on TCP port 80, cloud-init will time out and fail to run the script, leaving the application unconfigured. In real-world scenarios, overly restrictive network policies or misconfigured host-based firewalls are common causes of this issue.
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 CV0-004 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.
Operations and Support — This question tests Operations and Support — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: A firewall rule is blocking traffic to the metadata server IP address 169.254.169.254. — The error shown in the serial console output indicates that the instance cannot reach the metadata server at 169.254.169.254. This IP address is a link-local address used by cloud providers (e.g., AWS, GCP, Azure) to serve instance metadata, including user data scripts. If a firewall rule blocks traffic to this IP, the instance cannot retrieve its user data, causing the web application to fail to start or respond.
What should I do if I get this CV0-004 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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