Google ACE Practice Question: Ensuring successful operation of a cloud solution
This ACE practice question tests your understanding of ensuring successful operation of a cloud solution. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 receives a "Permission 'cloudfunctions.functions.call' denied" error when trying to invoke a Cloud Function from another service. 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 service account of the caller lacks the Cloud Functions Invoker role.
The error 'Permission cloudfunctions.functions.call denied' indicates that the Identity and Access Management (IAM) policy does not grant the caller the required permission to invoke the function. The Cloud Functions Invoker role (roles/cloudfunctions.invoker) specifically allows the `cloudfunctions.functions.call` permission, which is necessary for HTTP-triggered functions. Without this role on the caller's service account, any invocation attempt will be denied, regardless of other configurations.
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 of the caller lacks the Cloud Functions Invoker role.
Why this is correct
IAM permissions are required to invoke a function.
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 function is not deployed to the correct region.
Why it's wrong here
Would give a 'function not found' error, not permission denied.
✗
The Cloud Function has a CORS misconfiguration.
Why it's wrong here
CORS issues cause browser errors, not IAM permission errors.
✗
The VPC connector is not configured correctly.
Why it's wrong here
VPC connectors affect network routing, not permissions.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between IAM permission errors and network/configuration errors, so candidates mistakenly choose CORS or VPC options because they think invocation failures are always due to networking or browser restrictions, but the specific error message points directly to a missing IAM role.
Detailed technical explanation
How to think about this question
Under the hood, Cloud Functions uses IAM to evaluate the `cloudfunctions.functions.call` permission on the function resource before any request processing begins. This permission is distinct from the `cloudfunctions.functions.invoke` permission used for event-driven functions. In a real-world scenario, a service account used by Cloud Scheduler or a Compute Engine instance must have the Invoker role explicitly bound at the function level or project level; otherwise, even if the function is public, the caller's identity is denied. The error is returned as an HTTP 403 Forbidden with the specific message shown, which is a direct IAM denial, not a network or configuration 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 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this ACE question in full detail.
Ensuring successful operation of a cloud solution — This question tests Ensuring successful operation of a cloud solution — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The service account of the caller lacks the Cloud Functions Invoker role. — The error 'Permission cloudfunctions.functions.call denied' indicates that the Identity and Access Management (IAM) policy does not grant the caller the required permission to invoke the function. The Cloud Functions Invoker role (roles/cloudfunctions.invoker) specifically allows the `cloudfunctions.functions.call` permission, which is necessary for HTTP-triggered functions. Without this role on the caller's service account, any invocation attempt will be denied, regardless of other configurations.
What should I do if I get this ACE 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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