The most cost-effective solution is to establish five distinct inter-region VPC peering connections. Each of the five VPCs in the us-east-2 Region will be directly peered with the single VPC in the eu-west-1 Region. VPC peering is highly cost-effective as it does not incur hourly charges for the connection or data processing fees, which are characteristic of AWS Transit Gateway. The only cost associated with VPC peering is for the data transferred between the regions. This model precisely fulfills the connectivity requirements without the fixed operational costs of a more complex hub-and-spoke architecture using Transit Gateway, making it the most economical choice for this specific scenario.

A. An AWS Transit Gateway is a regional resource. It is not technically possible to attach a VPC from one region (us-east-2) directly to a Transit Gateway located in another region (eu-west-1).

B. While technically sound, this solution is not the most cost-effective. It requires two Transit Gateways and six attachments, all of which have hourly costs, in addition to data processing fees per gigabyte, making it more expensive than VPC peering.

C. A full mesh configuration is unnecessarily complex for this requirement. It would involve creating 15 peering connections, leading to significant management overhead and providing unneeded connectivity between the US-based VPCs.

1. AWS Documentation - What is VPC peering?: This document states

"A VPC peering connection is a networking connection between two VPCs... The VPCs can be in different Regions (also known as an inter-Region VPC peering connection)." It also clarifies that there are no gateway or VPN connection dependencies

highlighting its simpler cost structure.

Source: AWS VPC User Guide

"What is VPC peering?"

https://docs.aws.amazon.com/vpc/latest/peering/what-is-vpc-peering.html

2. AWS Transit Gateway Pricing: The official pricing page clearly shows that Transit Gateway has an hourly charge for each VPC attachment and a per-GB charge for data processing. In contrast

the Amazon VPC pricing page shows no such charges for VPC peering

only for inter-region data transfer.

Source: AWS Transit Gateway Pricing

https://aws.amazon.com/transit-gateway/pricing/

3. AWS Documentation - How transit gateways work: This document confirms the regional nature of Transit Gateways. "A transit gateway is a regional resource and can connect VPCs in the same Region." This directly invalidates option A.

Source: AWS VPC Transit Gateways Guide

"How transit gateways work"

https://docs.aws.amazon.com/vpc/latest/tgw/how-transit-gateways-work.html

4. AWS Whitepaper - Building a Scalable and Secure Multi-VPC AWS Network Infrastructure: This paper compares connectivity options. In the "VPC-to-VPC connectivity" section

it notes

"For a small number of VPCs

VPC peering is a very cost-effective way to provide... connectivity." This supports the choice of VPC peering as the most cost-effective solution for the scale described in the question.

Source: AWS Whitepapers & Guides

"VPC-to-VPC connectivity"

https://docs.aws.amazon.com/whitepapers/latest/building-scalable-secure-multi-vpc-network-infrastructure/vpc-to-vpc-connectivity.html