Exam AWS Certified Solutions Architect - Associate SAA-C03 topic 1 question 558 discussion

A VPC peering connection is a networking connection between two VPCs that enables you to route traffic between them using private IPv4 addresses or IPv6 addresses. Instances in either VPC can communicate with each other as if they are within the same network. You can create a VPC peering connection between your own VPCs, or with a VPC in another AWS account. The VPCs can be in different Regions (also known as an inter-Region VPC peering connection). https://docs.aws.amazon.com/vpc/latest/peering/what-is-vpc-peering.html#:~:text=A-,VPC%20peering,-connection%20is%20a

Transit Gateway network peering. VPC Peering to peer 2 or more VPC in the same region.

The key reasons are: VPC peering provides private connectivity between VPCs without using public IP space. Data transferred between peered VPCs is free as long as they are in the same region. 500 GB/month inter-VPC data transfer fits within peering free tier. Transit Gateway (Option A) incurs hourly charges plus data transfer fees. More costly than peering. Site-to-Site VPN (Option B) incurs hourly charges and data transfer fees. More expensive than peering. Direct Connect (Option D) has high hourly charges and would be overkill for this use case.

VPC peering is the most cost-effective solution

Communicating with two VPC in same account = VPC Peering

C is the correct answer. VPC peering is the most cost-effective way to connect two VPCs within the same region and AWS account. There are no additional charges for VPC peering beyond standard data transfer rates. Transit Gateway and VPN add additional hourly and data processing charges that are not necessary for simple VPC peering. Direct Connect provides dedicated network connectivity, but is overkill for the relatively low inter-VPC data transfer needs described here. It has high fixed costs plus data transfer rates. For occasional inter-VPC communication of moderate data volumes within the same region and account, VPC peering is the most cost-effective solution. It provides simple private connectivity without transfer charges or network appliances.