VPC Peering Connection Overview

What Is a VPC Peering Connection?

Figure 1 shows an application scenario of VPC peering connections.

• There are two VPCs (VPC-A and VPC-B) in region A that are not connected.
• Service servers (ECS-A01 and ECS-A02) are in VPC-A, and database servers (RDS-B01 and RDS-B02) are in VPC-B. The service servers and database servers cannot communicate with each other.

• You need to create a VPC peering connection (peering-AB) between VPC-A and VPC-B so the service servers and database servers can communicate with each other.

Figure 1 Two VPCs connected by a VPC peering connection

Currently, VPC peering connections are free.

VPC Peering Connection Creation Process

A VPC peering connection can only connect VPCs in the same region.

• If two VPCs are in the same account, the process of creating a VPC peering connection is shown in Figure 2.
  For details about how to create a VPC peering connection, see Creating a VPC Peering Connection to Connect Two VPCs in the Same Account.

  Figure 2 Process of creating a VPC peering connection between VPCs in the same account
  
• If two VPCs are in different accounts, the process of creating a VPC peering connection is shown in Figure 3.

  For details about how to create a VPC peering connection, see Creating a VPC Peering Connection to Connect Two VPCs in Different Accounts.

  If account A initiates a request to create a VPC peering connection with a VPC in account B, the VPC peering connection takes effect only after account B accepts the request.

  Figure 3 Process of creating a VPC peering connection between VPCs in different accounts
  

Notes and Constraints

• A VPC peering connection can only connect VPCs in the same region.
  • If you only need a few ECSs in different regions to communicate with each other, you can assign and bind EIPs to the ECSs.
• If the local and peer VPCs have overlapping CIDR blocks, the VPC peering connection may not be usable.
• By default, if VPC A is peered with VPC B that has EIPs, VPC A cannot use EIPs in VPC B to access the Internet. To enable this, you can use the NAT Gateway service or configure an SNAT server. For details, see Enabling Internet Connectivity for an ECS Without an EIP.