NAT Gateway Cost Traps and Cheaper Alternatives

The NAT Gateway Cost Trap

AWS NAT Gateways are convenient — they give private subnet instances internet access with zero maintenance. But at $0.045 per GB processed plus $0.045/hour ($32.40/month just to run), they silently become one of the largest line items on your AWS bill.

Understanding NAT Gateway Charges

• Hourly charge: $0.045/hr × 730 hrs = $32.85/month per NAT Gateway
• Data processing: $0.045/GB for every byte that traverses the gateway
• Multi-AZ setup: Most architectures deploy one per AZ, tripling the hourly cost

A typical production workload processing 500 GB/month through NAT Gateways in 3 AZs costs: (3 × $32.85) + (500 × $0.045) = $121/month. Scale that to terabytes and you're looking at thousands.

Alternative 1: VPC Gateway Endpoints (Free)

S3 and DynamoDB traffic often accounts for 40-60% of NAT Gateway bytes. VPC Gateway Endpoints route this traffic directly to the service without touching the NAT Gateway — and they're completely free.

aws ec2 create-vpc-endpoint \
  --vpc-id vpc-abc123 \
  --service-name com.amazonaws.us-east-1.s3 \
  --route-table-ids rtb-abc123

Alternative 2: VPC Interface Endpoints

For other AWS services (CloudWatch, SQS, SNS, ECR, etc.), Interface Endpoints keep traffic on the AWS backbone. At $0.01/GB processed + $0.01/hour, they're significantly cheaper than NAT Gateways for high-volume AWS API traffic.

Alternative 3: NAT Instances (for dev/test)

For non-production environments, a t3.micro NAT instance costs ~$7/month vs $32/month for a NAT Gateway. Use the AWS NAT AMI or configure iptables on a standard Amazon Linux instance.

Alternative 4: IPv6 Egress-Only Internet Gateway

If your workloads support IPv6, the Egress-Only Internet Gateway is free. It provides outbound IPv6 internet access without any per-GB processing charges.

Implementation Checklist

1. Analyze NAT Gateway usage in Cost Explorer (filter by NAT Gateway usage type)
2. Deploy S3 and DynamoDB Gateway Endpoints in all VPCs
3. Identify top AWS API callers and deploy Interface Endpoints for those services
4. Consider NAT instances for dev/staging environments
5. Monitor savings with weekly Cost Explorer reviews

Real-world result: After deploying Gateway Endpoints and 5 Interface Endpoints, one of our clients reduced NAT Gateway data processing from 2.1 TB/month to 400 GB/month — saving $76/month per environment.