AWS Data Transfer Traps That Drain Your Budget

You focused on the NAT Gateway processing fee ($0.045/GB). Good. But did you miss the other “handshakes” that tax your data as it moves?

Trap 1: Inter-Region Peering

If your VPC in us-east-1 talks to a VPC in us-west-2:

• Outbound: $0.02/GB.
• Inbound: $0.02/GB. Total cost to move a file: $0.04/GB.

Trap 2: Public IP to Public IP (in the same region)

If EC2 Instance A (Public IP) talks to EC2 Instance B (Public IP), and they are in the same region: AWS charges this as Data Transfer Out ($0.09/GB) because it technically leaves the VPC and comes back. Fix: Always use the Private IP address for internal communication. The cost drops to $0 (same AZ) or $0.01 (cross-AZ).

Trap 3: S3 via NAT Gateway

By default, traffic to S3 travels over the public internet (via the NAT Gateway).

• You pay: NAT Processing ($0.045/GB). Fix: Enable a VPC Gateway Endpoint for S3. It routes traffic privately.
• You pay: $0.00.

Conclusion

Networking costs are layers.

1. The Bandwidth (Internet).
2. The Device (NAT Gateway).
3. The Region (Cross-AZ/Cross-Region).

[!NOTE] Model the layers. Our NAT Gateway Calculator focuses on the NAT layer, which is usually the most expensive trap for private subnets.