Which solution will meet these requirements MOST cost-effectively?
Configure an S3 interface endpoint. Create a security group that allows outbound traffic to Amazon S3.
Configure an S3 gateway endpoint. Update the VPC route table to use the endpoint.
Configure an S3 bucket policy to allow traffic from the Elastic IP address that is assigned to the NAT gateway.
Create a second NAT gateway in the same subnet where the legacy application is deployed. Update the VPC route table to use the second NAT gateway.
Explanations:
Configuring an S3 interface endpoint would not fully meet the requirement since it involves sending traffic over the internet to reach the interface endpoint. This would not align with the security policy of preventing traffic from traversing the internet.
Configuring an S3 gateway endpoint allows the application in the private subnet to communicate with Amazon S3 directly without the traffic leaving the Amazon network. This is the most cost-effective solution as it eliminates data transfer costs associated with NAT gateways and does not require additional infrastructure.
While a bucket policy can control access, allowing traffic from the Elastic IP of the NAT gateway does not prevent traffic from traveling over the internet. This option does not align with the requirement of not having traffic cross the internet, as it would still route through the NAT gateway.
Creating a second NAT gateway would not help in meeting the requirement of keeping the traffic within the Amazon network. Traffic would still go out to the internet to reach S3, thus violating the security policy and incurring additional costs for the extra NAT gateway.
I appraise that the answer is:
Configure an S3 gateway endpoint. Update the VPC route table to use the endpoint.