What is the MOST cost-effective solution that meets these requirements?
Create a gateway VPC endpoint to provide connectivity to DynamoDB.
Configure a managed NAT gateway to provide connectivity to DynamoDB.
Establish an AWS Direct Connect connection between the private network and DynamoDB.
Deploy an AWS PrivateLink endpoint service between the private network and DynamoDB.
Explanations:
A gateway VPC endpoint allows resources in a VPC to connect to DynamoDB without requiring NAT instances, providing a fully managed, scalable, and cost-effective solution. It eliminates the need for ongoing management and reduces data transfer costs by keeping traffic within the AWS network.
A managed NAT gateway would still require ongoing costs for operation and management. Although it simplifies some aspects of using NAT instances, it does not eliminate the need for a NAT solution, which is contrary to the requirement to retire the existing NAT instances.
AWS Direct Connect establishes a dedicated connection to AWS, but it is not specifically designed for accessing DynamoDB. It also incurs additional costs and complexity and does not address the requirement for a solution that is easy to manage and cost-effective for accessing DynamoDB directly.
AWS PrivateLink provides private connectivity to services within AWS, but it is more complex and typically used for connecting to services hosted by other AWS accounts or third-party services. This option does not provide direct access to DynamoDB and may introduce additional management overhead.
I outline that the answer is:
Create a gateway VPC endpoint to provide connectivity to DynamoDB.