VPC-Peering

VPC Peering Explained with Diagram

VPC Peering allows two Virtual Private Clouds (VPCs) to communicate with each other privately using AWS’s internal network, without traversing the public internet. It enables secure, low-latency connections between VPCs in the same or different AWS accounts/regions.

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Key Features of VPC Peering

1. Private Connectivity – Traffic stays within AWS’s network.
2. No Single Point of Failure – Unlike VPN, it doesn’t rely on a gateway.
3. Cross-Account & Cross-Region Support – Can connect VPCs in different AWS accounts or regions.
4. No Transitive Peering – If VPC A is peered with VPC B, and VPC B is peered with VPC C, VPC A cannot talk to VPC C directly.
5. CIDR Block Restrictions – Peered VPCs must have non-overlapping IP ranges.

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VPC Peering Diagram

Here’s a simple illustration of VPC Peering between two VPCs:

+---------------------+          +---------------------+
|      VPC A          |          |      VPC B          |
|  (10.0.0.0/16)      | <------> |  (192.168.0.0/16)   |
|                     |          |                     |
| +----------------+  |          |  +----------------+ |
| |   Subnet 1     |  |          |  |   Subnet 1     | |
| | (10.0.1.0/24)  |  |          |  | (192.168.1.0/24)| |
| |   EC2 Instance |  |          |  |   EC2 Instance | |
| +----------------+  |          |  +----------------+ |
+---------------------+          +---------------------+
          ▲                                  ▲
          |                                  |
          ▼                                  ▼
+---------------------+          +---------------------+
|   Route Table A     |          |   Route Table B     |
| Destination: 192.168.0.0/16 |  | Destination: 10.0.0.0/16   |
| Target: pcx-123 (Peering) |  | Target: pcx-123 (Peering)  |
+---------------------+          +---------------------+

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How VPC Peering Works

1. Establish a Peering Connection

   • One VPC owner sends a peering request to another VPC (same/different account).
   • The other VPC owner must accept the request.

2. Update Route Tables

   • Both VPCs must add routes pointing to each other’s CIDR block via the peering connection (pcx-xxx).

3. Optional: Update Security Groups/NACLs

   • Ensure security groups allow traffic from the peered VPC’s IP range.

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Use Cases of VPC Peering

✔ Multi-tier applications – Connect frontend and backend VPCs.
✔ Shared services – Allow multiple VPCs to access a central database.
✔ Cross-account access – Securely link VPCs owned by different teams.

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Limitations

❌ No transitive peering (must set up direct connections).
❌ Overlapping CIDR blocks are not allowed.
❌ Region constraints – Inter-region peering may have higher latency.