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VPC Peering

A deep dive into VPC Peering - Practical ver.

Reference: aws docs



What is VPC Peering?

  • A feature that connects two different VPCs
    • Once two VPCs are connected, a pathway for internal communication is created!
  • Peering can also be configured across different accounts / different regions
    • Benefits of setting up peering connections between different regions
      • DR (Disaster Recovery) configuration becomes possible
      • You can peer multiple regions and use them
        • e.g.) Accessing a Thailand service from within the country


Working with VPC Peering

  • Requester VPC & Accepter VPC
    • Although the names are requester and accepter, they do not indicate direction!
      • Direction can be configured differently based on subnet communication
  • Sending VPC's CIDR Block >= Receiving VPC's CIDR Block
    • Why?
      • If the receiving VPC's CIDR Block is larger than the sending VPC's CIDR Block, communication obviously won't work!
    • Typically, the CIDR Blocks of both VPCs are set to be the same, but the receiving VPC's can be smaller
      • Being smaller is not a problem


Things you should be aware of

  1. When configuring a Peering Connection, the CIDR Blocks of the two VPCs must not conflict

    • Why?
      • Since the two VPCs are being connected rather than existing separately, they cannot have conflicting CIDRs

  2. Additional charges apply when traffic passes through the peering connection

    • However, it's not a significant amount!