Which solution will meet these requirements?
Use the internet gateway of the VPC to access the DynamoDB table. Use the ALB to route the traffic to the EC2 instances.
Add a NAT gateway in one of the public subnets of the VPC. Configure the security groups of the EC2 instances to access the DynamoDB table through the NAT gateway.
Use the Site-to-Site VPN connection to route all DynamoDB network traffic through the on-premises network infrastructure to access the EC2 instances.
Create a VPC endpoint for DynamoDB. Assign the endpoint to the route table of the private subnets that contain the EC2 instances.
Explanations:
Using the internet gateway would expose the traffic to the public internet, which is not secure for accessing DynamoDB from private subnets. The ALB only routes traffic to EC2 instances, not to external services like DynamoDB.
Although a NAT gateway enables access to DynamoDB, it introduces unnecessary costs and overhead for internet routing. A VPC endpoint is more secure and cost-effective for private subnet access to DynamoDB.
Routing DynamoDB traffic through the on-premises network over a VPN is inefficient and complex, adding latency and potential bottlenecks, especially since DynamoDB can be accessed directly within AWS using a VPC endpoint.
A VPC endpoint allows private and secure access to DynamoDB within the VPC, avoiding the public internet. It integrates with the VPC route table for private subnets, making it the optimal solution for this requirement.
From my point of view, the answer is:
Create a VPC endpoint for DynamoDB. Assign the endpoint to the route table of the private subnets that contain the EC2 instances.