Answer: Enable VPC Service Controls, create a perimeter with Project A and B, and include Cloud Storage service.

The question requires ensuring that a Cloud Storage bucket in Project A is only readable from Project B and preventing data exfiltration to external Cloud Storage buckets, even with valid credentials. Option A (VPC Service Controls) is the correct choice because it creates a security perimeter that restricts data movement and access to only the specified projects (A and B) and services (Cloud Storage), effectively preventing access from outside the perimeter. This aligns with the community consensus, where A has 100% support and high upvotes, with references to Google's VPC Service Controls documentation highlighting its use for isolation and data exfiltration prevention. Option B (Domain Restricted Sharing and Bucket Policy Only) is insufficient as it only restricts sharing based on domains and does not prevent data copying to external buckets with credentials. Option C (Private Access with firewall rules) limits network access but does not block API-based access to Cloud Storage from outside the network. Option D (VPC Peering with firewall rules) enables network connectivity between projects but does not prevent data access or copying via Cloud Storage APIs from external sources.

Author: LeetQuiz Editorial Team