Creating a Service Account with the necessary permissions to list Compute Engine instances should be approached with the principle of least privilege in mind. This principle encourages granting a Service Account only the permissions necessary to perform its functions, reducing the risk of over-privileging.
The recommended approach involves creating a custom role that includes the specific permission compute.instances.list. By doing this, the Service Account will have just the right permissions to list instances without having unnecessary capabilities that come with broader roles. This granular control helps enhance security by limiting what the Service Account can access and perform.
Utilizing a custom role ensures that you can tailor the access specifically to the needs of your application or service, thus maintaining a secure environment. It avoids situations where the Service Account might accidentally perform actions beyond what is required, which can happen with broader permissions from predefined roles.