A solution architect is designing an AWS account structure for a company that consists of multiple terms. All the team will work in the same AWS Region. The company needs a VPC that is connected to…

Using AWS CloudFormation to provision the VPC and required subnets ensures a consistent, automated, and repeatable infrastructure setup, which reduces manual errors and operational overhead, contributing to overall cost-effectiveness and manageability of the account structure.

For connectivity to an on-premises network with less than 50 Mbps traffic, an AWS Site-to-Site VPN is a highly cost-effective solution compared to Direct Connect. Combining it with AWS Transit Gateway centralizes the network hub, allowing multiple teams or VPCs (present or future) to connect to the on-premises network through a single VPN connection, simplifying management and reducing costs in a multi-team environment.

While an AWS Site-to-Site VPN alone provides connectivity, for a company with "multiple teams," using it in conjunction with AWS Transit Gateway (as in option C) offers a more scalable and centrally managed approach for connecting potentially multiple VPCs to the on-premises network, making it more cost-effective for future expansion than individual VPN connections.

AWS Direct Connect provides dedicated network connectivity but is significantly more expensive than an AWS Site-to-Site VPN, especially for bandwidth requirements less than 50 Mbps, thus not meeting the "MOST cost-effectively" requirement.