The correct approach is to use a VPC endpoint for DynamoDB. A VPC endpoint allows private communication between your VPC and supported AWS services without requiring an internet gateway, NAT gateway, or NAT instance. Specifically, a Gateway VPC endpoint supports services like DynamoDB and S3, ensuring that all traffic remains within the AWS network while providing highly secure and low-latency access.

Why the other options are incorrect:

Using a NAT gateway in a public subnet enables internet-bound traffic for resources in private subnets, but the traffic is routed through the public internet, even if it is encrypted. This violates the requirement to keep traffic within the AWS network and introduces unnecessary exposure and cost.

Using a NAT instance in a private subnet is technically incorrect and operationally inefficient. NAT instances require careful management, can become bottlenecks, and, like NAT gateways, send traffic through the public internet.

Using the internet gateway attached to the VPC would force traffic out of the private subnet and over the internet, which completely fails the security requirement to avoid public internet exposure. EC2 instances in private subnets cannot even route directly through an internet gateway without public IPs and specific route table configurations.

Why this question is important: This scenario tests your knowledge of secure and efficient connectivity between private AWS resources and AWS services like DynamoDB. It's especially relevant for regulated industries where security and compliance are paramount.

Exam tip: Always look for VPC endpoints when a question emphasizes security, private communication, and avoiding public internet traffic to AWS services like S3 or DynamoDB. NAT solutions are more appropriate when accessing third-party APIs or services outside AWS.

Full AWS Practitioner Certification Question