Which solution will meet these requirements with the LEAST administrative overhead?
Deploy software VPN tunnels between the application VPCs and the shared services VPC. Add routes between the application VPCs in their subnets to the shared services VPC.
Deploy VPC peering connections between the application VPCs and the shared services VPC. Add routes between the application VPCs in their subnets to the shared services VPC through the peering connection.
Deploy an AWS Direct Connect connection between the application VPCs and the shared services VPAdd routes from the application VPCs in their subnets to the shared services VPC and the applications VPCs. Add routes from the shared services VPC subnets to the applications VPCs.
Deploy a transit gateway with associations between the transit gateway and the application VPCs and the shared services VPC. Add routes between the application VPCs in their subnets and the application VPCs to the shared services VPC through the transit gateway.
Explanations:
Deploying software VPN tunnels requires managing multiple VPN connections and configurations, which increases administrative overhead, especially with a larger number of applications. Additionally, routing between isolated VPCs via VPN can complicate traffic flow and management.
While VPC peering allows communication between VPCs, it can lead to complex management when scaling to a large number of applications. Each VPC would require a separate peering connection, making routing and oversight cumbersome as more applications are added.
AWS Direct Connect is primarily used for establishing a dedicated connection to on-premises networks, which is not suitable for communication between multiple VPCs in the scenario. It introduces additional complexity and is not the most efficient method for inter-VPC communication.
A transit gateway simplifies the architecture by allowing multiple VPCs to communicate through a single gateway. This greatly reduces administrative overhead as it centralizes routing and scaling, making it easier to manage as more applications are migrated to AWS. It supports efficient inter-VPC communication with minimal configuration.
From my perspective, the answer is:
Deploy a transit gateway with associations between the transit gateway and the application VPCs and the shared services VPC. Add routes between the application VPCs in their subnets and the application VPCs to the shared services VPC through the transit gateway.