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 store objects. Security policy requires that traffic from the application must not traverse the internet. Which solution meets these requirements MOST cost-effectively?

An S3 gateway endpoint allows private connectivity from your VPC to Amazon S3 without requiring an internet gateway, NAT device, VPN connection, or AWS Direct Connect connection. This ensures traffic does not traverse the internet, meeting the security requirement. Gateway endpoints are also free of charge, making this the most cost-effective solution. Configuring an S3 interface endpoint would also work but is more expensive as interface endpoints incur hourly charges and data processing charges. Configuring an S3 bucket policy to allow traffic from the NAT gateway's Elastic IP would still route traffic through the NAT gateway and potentially the internet, violating the security policy. Creating a second NAT gateway is unnecessary and would increase costs without addressing the requirement to avoid internet traversal for S3 traffic.