Data transferred “in” to and “out” from public or Elastic IPv4 address is charged at $0.01/GB in each direction.

https://aws.amazon.com/ec2/pricing/on-demand/

So, depend on traffic flow.

Hi, Yes, you will incur costs as per https://aws.amazon.com/ec2/pricing/on-demand/#Data_Transfer ``` Data transferred "in" to and "out" from Amazon EC2, Amazon RDS, Amazon Redshift, Amazon DynamoDB Accelerator (DAX), and Amazon ElastiCache instances, Elastic Network Interfaces or VPC Peering connections across Availability Zones in the same AWS Region is charged at $0.01/GB in each direction. IPv4: Data transferred "in" to and "out" from public or Elastic IPv4 address is charged at $0.01/GB in each direction. IPv6: Data transferred "in" to and "out" from an IPv6 address in a different VPC is charged at $0.01/GB in each direction. ``` Note: in you case, both ends will pay the fee in or out for a transfer. Best, Didier

is it true that you are charged in both the zones Yes - 1GB of transfer is charged twice. Each end costs $0.01 - so you pay $0.02/1GB. I was checking Azure and GCP documentation and it seems it is not the case with these two providers where you will be charged for data transferred out from the a zone only Azure doesn't charge for data transfer between availability zones at all. GCP indeed charges only for the egress, at the same price as AWS - but since it's only for egress it's effectively half-price. Is it something which AWS has for a long time Yes - I don't know exactly how long but it's been around for years at least.

Managing cross-region data transfer costs in AWS requires careful consideration of your architecture and placement of your resources. Although it’s easy to overlook, cross-region data transfers can significantly impact your AWS bill if not optimized properly. Here are some of the strategies you can implement to reduce these costs: 1. Utilize Amazon CloudFront for Caching and Content Delivery If you're distributing content globally, consider using Amazon CloudFront. By caching your data at AWS Edge Locations, you can reduce the amount of data transferred between regions. This is particularly useful if you’re serving static or dynamic content to users worldwide. Instead of routing requests directly to your origin (like an S3 bucket in a single region), CloudFront serves the content from the closest edge location, minimizing cross-region data transfers. 2. AWS Global Accelerator for Cross-Region Performance and Cost Efficiency Another approach is to implement AWS Global Accelerator, which improves the performance and availability of your applications across multiple regions by using the AWS global network backbone. Global Accelerator routes your traffic to the optimal endpoint, reducing latency and potentially minimizing public internet usage, which can lower data transfer costs. Although this service comes with its own costs, it can often pay off in scenario with heavy cross-region traffic. 3. Make use of S3 Transfer Acceleration for Speed and Efficiency For moving large amounts of data to and from S3 buckets across distant regions, enabling S3 Transfer Acceleration can be an effective solution. This will help you route data through Amazon CloudFront globally edge locations, which will speed up transfers and reducing latency. It's important to note there’s also cost associated with using Transfer Acceleration, it can reduce the overall expense of moving large datasets between regions, particularly if your regions are geographically distant dispersed. 4. Make use VPC Peering or AWS Transit Gateway for Inter-Region Traffic Dependiing on your architecture, when running applications across multiple VPCs in different regions, VPC Peering or AWS Transit Gateway can help you manage traffic more efficiently and cost-effectively. VPC Peering allows direct communication between VPCs without going over the public internet. While this reduces costs, it’s better suited for point-to-point connections. AWS Transit Gateway, on the other hand, provides a central hub for managing traffic between multiple VPCs and regions, enabling to easily route traffic across regions without needing multiple VPC Peering connections. This helps simplify your network architecture and can lead to cost savings if you have many VPCs communicating across regions. 5. Reduce Redundant Transfers and Optimize Data Workflows Remember one great way to reduce costs is to minimize unnecessary data transfers all together. Analyze your architecture to ensure you’re not transferring the same data multiple times across regions. Data compression before transferring can reduce the overall amount of data moved. One method is to only transfer the changed data nstead of full data transfer, this can also help reduce bandwidth and costs. 6. Monitor Costs Using tools like, AWS Cost Explorer, AWS Trusted Advisor AWS provides several tools to help you monitor and optimize your data transfer costs. **AWS Cost Explorer** allows you to analyze your usage patterns and gives you a breakdown into the services contributing to higher data transfer charges. Additionally, you can also make use of AWS Trusted Advisor to get recommendations on cost. Or use tools with dashboards to properly monitor your data transfer cost. .

Data transfer charges in AWS can be complex, but I'll break it down for you: 1. Data transfer within AWS: - Within the same Availability Zone (AZ) in a region: Generally free between EC2 instances, RDS, Redshift, ElastiCache, and Elastic Network Interfaces. - Between AZs in the same region: Charged at $0.01/GB in each direction. - Between AWS regions: Charged at inter-region data transfer rates, which vary depending on the specific regions involved. 2. Data transfer to/from the Internet: - Inbound data transfer (from the Internet to AWS): Free - Outbound data transfer (from AWS to the Internet): Charged based on a tiered pricing model. The first 100 GB per month is typically free for all users, aggregated across all AWS services and regions (except China and GovCloud). 3. Data transfer to external services: When your EC2 instance makes API requests to external services like Gemini API or Supabase, this is considered outbound data transfer to the Internet. You'll be charged for the data sent from your EC2 instance to these external services, as well as the data received in response. The charges will appear in your bill with a UsageType of "Region-DataTransfer-Out-Bytes" (e.g., USE2-DataTransfer-Out-Bytes for data transfer out of the US East (Ohio) region). Keep in mind that the actual costs can vary based on your specific region, the amount of data transferred, and any special pricing or free tier benefits you may have. To optimize costs, consider using services within the same region and AZ when possible, and monitor your data transfer using tools like AWS Cost Explorer. **Sources** Understanding data transfer charges - AWS Data Exports Help to understand data transfer between AWS zones | AWS re:Post Data Transfer Pricing | AWS re:Post Amazon EC2 FAQs – AWS Exploring Data Transfer Costs for Classic and Application Load Balancers | Networking & Content Delivery