A company runs an application in a private subnet behind an Application Load Balancer (ALB) in a VPC. The VPC has a NAT gateway and an internet gateway. The application calls the Amazon S3 API to stor

An S3 interface endpoint (powered by AWS PrivateLink) provides private connectivity to S3 via ENIs, but it is generally more expensive than a gateway endpoint, making it not the MOST cost-effective option for S3.

An S3 Gateway Endpoint provides reliable and private connectivity to S3 from instances within a VPC without requiring an internet gateway or NAT gateway. By configuring an S3 Gateway Endpoint and updating the VPC route table, traffic destined for S3 will be routed directly within the AWS network, fulfilling the security requirement to avoid the internet and being the most cost-effective solution for this specific service.

Configuring an S3 bucket policy to allow traffic from a NAT Gateway's Elastic IP address would still involve traffic traversing the internet via the NAT gateway and internet gateway, violating the security policy.

Creating a second NAT gateway would not change the fact that S3 traffic would still traverse the internet, and it would incur additional costs without solving the core security requirement.