Hidden AWS costs from NAT Gateways and cross-zone data transfers can be significant

A significant portion of AWS spending for mid-sized platforms can be attributed to untagged NAT Gateway and inter-Availability Zone data transfer costs. These costs are often overlooked as they are grouped under the EC2-Other billing line item. They accumulate from architectural choices like cross-zone application traffic and data routed through NAT Gateways unnecessarily. The article outlines methods to identify these expenses using AWS Cost Explorer and VPC Flow Logs. It also suggests mitigation strategies such as implementing VPC endpoints and zone-aware routing.