Which solution will meet this requirement?

Explanations:

While VPC peering can enable connectivity between the company’s and vendor’s VPCs, the vendor must be part of the AWS Hosted Connection Direct Connect Program, which is not required for VPC peering. Additionally, there is no internet gateway or VPN connection in the company’s VPC, making this option infeasible.

A client VPN connection allows remote access to resources, but it does not establish direct network connectivity between two VPCs. Moreover, without an existing VPN connection or Direct Connect, this solution does not provide a viable way to connect the company’s VPC with the vendor’s VPC.

Creating a Network Load Balancer (NLB) in front of the RDS allows for the use of AWS PrivateLink, which enables private connectivity between the company’s VPC and the vendor’s VPC without needing an internet gateway or VPN connection. This solution effectively meets the requirement.

While AWS Transit Gateway is a powerful service for connecting multiple VPCs, it requires both VPCs to be in the same AWS account or appropriately configured sharing. Since the vendor’s RDS is in a different account, and the company lacks the necessary connection infrastructure, this option is not feasible.