A company has multiple business units that each run applications in separate AWS accounts and application VPCs in the same Region. Those applications must consume data from a central shared services VPC. The company requires granular security controls and an architecture that can scale as more business units connect to the shared services VPC. Which solution is the most secure and scalable?

Publishing VPC endpoint services with AWS PrivateLink is the most secure and scalable solution. PrivateLink allows application VPCs to securely access services in the shared services VPC without traversing the public internet or requiring VPC peering. This provides granular control, as each application VPC only gets access to specific services through an interface endpoint, not the entire shared services VPC. It scales well because adding new business units only requires creating new endpoints, not managing complex routing or peering connections. Creating a central Transit Gateway with full-mesh connectivity would allow all VPCs to communicate, which violates the requirement for granular security controls. Establishing VPC peering between each application VPC and the shared services VPC becomes unmanageable and less secure as the number of VPCs grows, as it creates a many-to-many peering relationship. Building a central transit VPC with a VPN appliance introduces a single point of failure, requires managing a third-party appliance, and is less scalable and more complex than native AWS solutions like PrivateLink.