Google PCA Manage implementation of cloud architecture Practice Question
A company has a Cloud Run service that processes images uploaded by users. The service reads the images from a Cloud Storage bucket and writes processed images to another bucket. The team recently updated the service to use a custom service account named 'image-processor-sa' with minimal permissions. After the update, the service fails with permission errors when trying to read from the source bucket. The team verified that the service account has the Storage Object Viewer role on the source bucket and Storage Object Creator role on the destination bucket. What should the architect do to resolve the issue?
⚠ Common exam trap
Google Cloud often tests the distinction between granting permissions to a service account versus actually attaching that service account to a resource; candidates mistakenly assume that creating and granting roles to a service account automatically makes it the active identity of the Cloud Run service.
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
✓
Ensure the Cloud Run service uses the correct service account by redeploying with the --service-account flag set to 'image-processor-sa@project-id.iam.gserviceaccount.com'.
The error occurs because the Cloud Run service is not using the custom service account 'image-processor-sa' despite it being created and granted permissions. By default, Cloud Run uses the Compute Engine default service account unless explicitly overridden. Redeploying with the --service-account flag attaches the correct identity to the Cloud Run revision, allowing it to authenticate with Cloud Storage using the minimal permissions already assigned.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Ensure the Cloud Run service uses the correct service account by redeploying with the --service-account flag set to 'image-processor-sa@project-id.iam.gserviceaccount.com'.
Why this is correct
Cloud Run defaults to the Compute Engine default service account unless explicitly overridden, so the new permissions were never applied. Redeploying with the --service-account flag binds the revision to image-processor-sa, letting its Storage Object Viewer role take effect.
- ✗
Grant the service account the Cloud Run Invoker role on the Cloud Run service.
Why it's wrong here
Cloud Run Invoker governs who may call the service, not what the service's identity can do to Cloud Storage, so it cannot fix the read failure. It is tempting because the error surfaced after a service-account change, but Invoker applies to inbound invocation, not outbound bucket access.
- ✗
Assign the Storage Admin role to the service account.
Why it's wrong here
Storage Admin grants far more than the read the service needs, violating least privilege, and the missing permission is on the bucket's IAM binding, not the role's scope. It is tempting because a broad role often masks an underlying misconfiguration, but it over-provisions rights.
- ✗
Enable the Cloud Storage API for the project.
Why it's wrong here
The Storage API is already enabled, since the service previously read and wrote objects successfully; disabling it would break all bucket operations, not just this identity's reads. It is tempting because API enablement is a common first check for permission-style errors on new projects.
Visual reference
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Related to this question
Learn chapter
Cloud Storage: Objects and Buckets
Key term
Compute Engine
Compute Engine is Google Cloud's Infrastructure-as-a-Service (IaaS) offering that lets you create and run virtual machines on Google's infrastructure.
Key term
Service
A service is a software component or system that performs a specific function and is available to be used by other programs or users over a network.
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Written by Johnson Ajibi, MSc IT Security
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