[AWS] Connecting VPCs

There are a couple of ways to connect instances and services in one VPC with other VPCs. – VPC Peering, Open VPC to the Internet, or AWS PrivateLink.

Opening applications and services in one VPC to other VPCs

• Open the VPC to the Internet
  • Everything is in public
    • Make subnets public
  • Not a good idea due to security issues

• VPC Peering
  • Need to create and manage many peering relationships.
  • Management Overhead
  • All applications in a VPC are open.

• AWS PrivateLink
  • It is the best way to expose a service VPC to many other VPCs.
  • It keeps all the network traffic within the AWS network.
  • It requires a Network Load Balancer on the service VPC and an ENI(Elastic Network Interface) on the customer VPC.
    • It does not require VPC peering, route tables, NAT gateways, nor internet gateways.

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Communication between two EC2 instances

• EC2 instances in the same region: Traffic stays in the AWS network.
• EC2 instances in the different regions with Inter-Region VPC Peering connection: Traffic stays in the AWS network.
• EC2 instances in the different regions WITHOUT Inter-Region VPC Peering connection: There is no guarantee that traffic stays within the AWS network.

EC2 instances in one region can communicate with EC2 instances in another region using:

• Inter-Region VPC Peering
• Public IP addresses
• NAT gateway
• NAT instances
• VPN Connections
• or Direct Connect connections