Glossary
The service through which resources in private subnets reach the internet. Billed per hour and per gigabyte processed.
A NAT gateway costs a base fee per hour plus a charge per gigabyte passing through. Together that makes it one of the least conspicuous large items on an AWS bill.
It usually becomes expensive not through real internet traffic but through calls to AWS services that travel over the internet instead of a private endpoint.
How you notice it
Frequently asked
For S3 and DynamoDB set up a gateway endpoint, which is free and routes traffic past the NAT. For other AWS services there are interface endpoints, which cost per hour but save the data transfer. What remains is genuine internet traffic, and that is usually small.