AWS Network Cost Structure Analysis: Double Billing of Data Transfer and Processing Fees and Optimization Strategies

AWS network costs consist of two axes: Data Transfer and Data Processing, and both fees can be charged simultaneously for the same traffic. For example, when a private EC2 instance transfers data to the internet via a NAT Gateway, the processing fee of $0.059/GB and the transfer fee of $0.126/GB are combined, resulting in a total charge of $0.185/GB. These network costs account for 8~12% of customer bills, making optimization at the design stage essential.

Principles and Exceptions of Data Transfer Fees

The basic principle of data transfer is that outbound to the internet (DTO) is charged while inbound (DTI) is free. However, transfer between Availability Zones (AZs) within the same region is charged $0.01 in each direction. In particular, when using public IPs or Elastic IPs, communication within the same AZ incurs the same $0.01 fee as inter-AZ transfer due to the routing path, so using private IPs is recommended. Inter-region transfer is charged based on the source region; transferring from Seoul to us-east-1 costs $0.08/GB, while the reverse direction costs $0.02/GB.

NAT Gateway Cost Structure and Bypass Strategies

NAT Gateway charges a fixed fee of $0.059 per hour and a processing fee of $0.059 per GB. When EC2 instances in private subnets access AWS services in the same region such as S3 and ECR, data transfer fees are free, but NAT Gateway processing fees still apply. For 10TB of monthly traffic, the total NAT Gateway cost is approximately $1,937, with NAT processing and fixed fees accounting for about 33%.

To reduce costs, the following VPC Endpoint strategies can be utilized:

• Gateway Endpoints: Exclusive to S3 and DynamoDB, these bypass NAT Gateway at $0 cost by modifying only the routing table without ENIs.
• Interface Endpoints: Used for other AWS services, these are more cost-effective than NAT Gateway when monthly traffic per AZ exceeds approximately 194GB. The processing fee is $0.01/GB, which is 1/6 of the NAT fee.
• Per-AZ Deployment: NAT Gateways should be deployed in each AZ with separate routing tables to prevent additional fees caused by inter-AZ communication.

IPv4 Address Costs and CloudFront Utilization

Since February 2024, all public IPv4 addresses incur a cost of $0.005 per hour (approximately $3.65 per month). It is necessary to release idle Elastic IPs and review unnecessary public IP allocations. Utilizing CloudFront for internet traffic optimization can reduce origin traffic to 1/5 with an 80% cache hit rate, and through Korean edge locations, services can be provided at $0.120/GB, which is cheaper than direct transfer to the Seoul region ($0.126/GB).