You manage one of your organization's Google Cloud projects (Project A).

When dealing with VPC Service Controls (VPC SC), it's important to ensure that only authorized resources can access sensitive data and services. To allow a resource in Project B to access Pub/Sub in Project A without compromising security, you should configure an ingress policy for the service perimeter in Project A.

Identify the Service Account: Determine the service account in Project B that requires access to the Pub/Sub topic in Project A.

Configure Ingress Policy:

Go to the Google Cloud Console.

Navigate to Security > VPC Service Controls.

Select the service perimeter for Project A.

Add an ingress rule specifying the service account from Project B and allowing it access to the necessary Pub/Sub resources.

Define Conditions: Ensure that the ingress policy adheres to the principle of least privilege, granting only the necessary permissions to collect messages from the Pub/Sub topic.

Save and Apply: Save the policy and apply the changes to enforce the new access controls.

This approach maintains the security boundaries set by VPC SC while enabling the required access from Project B to Project A.

VPC Service Controls Documentation

Configuring Ingress Policies