This PCSE practice question tests your understanding of pcse exam topics. 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 security engineer runs the commands shown. The command 'gcloud compute instances list' fails with a permission denied error. The service account key belongs to a service account with the role 'roles/compute.viewer' on the project. 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.
Network Topology
A
The role 'roles/compute.viewer' does not include the permission to list instances.
Why wrong: It does include compute.instances.list.
B
The service account key file is invalid or the service account has been deleted.
Most likely cause: the key is invalid, causing authentication failure.
C
The command 'gcloud auth activate-service-account' should be 'gcloud auth login' instead.
Why wrong: Activate-service-account is the correct command for service account authentication.
D
The project 'my-project' does not exist or the service account is not in that project.
Why wrong: If the project didn't exist, gcloud config set would fail; but the error is on list command.
The answer is that the service account key file is invalid or the service account has been deleted. This is the most likely cause because the `gcloud auth activate-service-account` command relies on a valid, unexpired key file to establish identity; if the key is corrupted, malformed, or the underlying service account no longer exists, authentication silently fails, leading to a permission denied error on subsequent commands like `gcloud compute instances list` even though the `roles/compute.viewer` role is correctly assigned. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding that IAM authorization depends on successful authentication first—a common trap is to assume the error stems from insufficient permissions when the real issue is a broken identity proof. Remember the memory tip: “Auth before Authz”—if authentication fails, no amount of roles will help.
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
✓
The service account key file is invalid or the service account has been deleted.
The command 'gcloud auth activate-service-account' uses a service account key file to authenticate as that service account. If the key file is invalid (e.g., corrupted, expired, or malformed) or the service account itself has been deleted, authentication will fail, causing subsequent commands like 'gcloud compute instances list' to return a permission denied error even if the service account has the correct role. The error is not about missing permissions on the role, but about the inability to prove identity.
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 role 'roles/compute.viewer' does not include the permission to list instances.
Why it's wrong here
It does include compute.instances.list.
✓
The service account key file is invalid or the service account has been deleted.
Why this is correct
Most likely cause: the key is invalid, causing authentication failure.
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 command 'gcloud auth activate-service-account' should be 'gcloud auth login' instead.
Why it's wrong here
Activate-service-account is the correct command for service account authentication.
✗
The project 'my-project' does not exist or the service account is not in that project.
Why it's wrong here
If the project didn't exist, gcloud config set would fail; but the error is on list command.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between authentication failure (invalid key/deleted account) and authorization failure (insufficient permissions), tricking candidates into assuming the role itself is missing a permission when the real issue is that the identity cannot be verified.
Trap categories for this question
Command / output trap
Activate-service-account is the correct command for service account authentication.
Detailed technical explanation
How to think about this question
When 'gcloud auth activate-service-account' is run, it uses the private key from the JSON key file to generate a signed JWT (JSON Web Token) that is exchanged for an OAuth 2.0 access token from Google's token endpoint. If the key file is invalid (e.g., incorrect format, expired key, or revoked) or the service account has been deleted, the token request fails with a 400 or 401 error, and gcloud stores no valid credentials. Subsequent API calls then fail with a 403 permission denied because no authenticated identity is associated with the request. This is distinct from a role-based permission denial, which would occur only after successful authentication.
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.
Read the scenario before looking for a memorised answer.
What is the correct answer to this question?
The correct answer is: The service account key file is invalid or the service account has been deleted. — The command 'gcloud auth activate-service-account' uses a service account key file to authenticate as that service account. If the key file is invalid (e.g., corrupted, expired, or malformed) or the service account itself has been deleted, authentication will fail, causing subsequent commands like 'gcloud compute instances list' to return a permission denied error even if the service account has the correct role. The error is not about missing permissions on the role, but about the inability to prove identity.
What should I do if I get this PCSE 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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