78. Transit Gateway

i. Allows to have transitive peering between thousands of VPCs and on-premises data centers.
ii. Works on a hub and spoke model
iii. Works on a regional basis, but we can have it across multiple regions.
iv. We can use it across multiple AWS accounts using RAM
v. We can use route tables to limit how VPCs talk to one another.
vi. Works with Direct Connect as well as VPN connections.
vii. Supports IP multicast (not supported by any other AWS service)
viii. A transit gateway is a network transit hub that you can use to interconnect your virtual private clouds (VPC) and on-premises networks. A transit gateway by itself cannot establish a low latency and high throughput connection between a data center and AWS Cloud.

Question 01:
A company has many VPC in various accounts, that need to be connected in a star network with one another and connected with on-premises networks through Direct Connect.
What do you recommend?
• VPC Peering
• VPN Gateway
• Transit Gateway (Correct)
• Private Link
Correct option:
Transit Gateway
AWS Transit Gateway is a service that enables customers to connect their Amazon Virtual Private Clouds (VPCs) and their on-premises networks to a single gateway. With AWS Transit Gateway, you only have to create and manage a single connection from the central gateway into each Amazon VPC, on-premises data center, or remote office across your network. Transit Gateway acts as a hub that controls how traffic is routed among all the connected networks which act like spokes. So, this is a perfect use-case for the Transit Gateway.
Incorrect options:
VPC Peering – 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 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). VPC Peering helps connect two VPCs and is not transitive. It would require to create many peering connections between all the VPCs to have them connect. This alone wouldn’t work, because we would need to also connect the on-premises data center through Direct Connect and Direct Connect Gateway, but that’s not mentioned in this answer.
VPN Gateway – A virtual private gateway (also known as a VPN Gateway) is the endpoint on the VPC side of your VPN connection. You can create a virtual private gateway before creating the VPC itself. VPN Gateway is a distractor here because we haven’t mentioned a VPN.
Private Link – AWS PrivateLink simplifies the security of data shared with cloud-based applications by eliminating the exposure of data to the public Internet. AWS PrivateLink provides private connectivity between VPCs, AWS services, and on-premises applications, securely on the Amazon network. Private Link is utilized to create a private connection between an application that is fronted by an NLB in an account, and an Elastic Network Interface (ENI) in another account, without the need of VPC peering, and allowing the connections between the two to remain within the AWS network.