In this lesson, we will discuss Using VPC Peering for Inter and intra-Regional Communication. Although we can use technologies such as site-to-site VPNs to connect our AWS VPCs together, there are significant drawbacks of this approach. Drawbacks such as device management; you will need to deploy at least one virtual appliance to create your site-to-site VPN. You'll be responsible for the high availability of this device and there'll also be a cost for this device. Data flowing through the Internet; because you are creating a site-to-site VPN, your traffic will travel across public networks and be susceptible to delay and potential attack.

Bandwidth bottlenecks; because you are using a virtual appliance, the virtual appliance can become a bandwidth bottleneck due to the max bandwidth limits for EC2 instances. Data out charges; you'll be charged for data leaving the region. VPC peering removes most of these drawbacks. VPC peering is used to connect a pair of VPCs into a single routing domain.

VPC peering can be used to peer VPCs in the same or different regions. When using VPC peering, traffic traversing a VPC peering connection always stays on the AWS Backbone, reducing the likelihood of your data being accepted. Traffic traversing a VPC peering connection is always encrypted, and when using VPC peering, there is no device for you to manage, there is no single point of failure, and no bandwidth bottlenecks. There is no charge for the VPC peering connection itself, but there is a data charge for data traversing the VPC peering connection. A VPC peering connection is only used to peer a pair of VPCs. VPC peering does not care whether VPCs are in the same region, in different regions, in the same AWS account, or in different AWS accounts. One big rule for us to remember, in order to peer a pair of VPCs using VPC peering, the VPCs must use non-overlapping IP ranges. Two of VPC peering characteristics worth knowing: VPC peering connections are non-transitive. If VPC A and VPC B are peered, and VPC B and VPC C are peered, VPC A and VPC C are not.

In order to route traffic between VPC A and VPC C, you could peer the VPCs directly with each other. Peered VPCs cannot share Internet gateways or virtual private gateways. If you have multiple VPCs that need to connect to the Internet or to on-premises, then they must have their own gateways or connect using transit gateway. VPC peering works really well when you have a small number of VPCs to interconnect. But as your number of VPCs grow, the more VPCs that you have that need to connect to on-premises and the Internet, the more complex your route environment is, then the more likely you are to use transit gateways.