A multi-account environment has one account per microservice. Each microservice runs in its own VPC with EC2 instances behind an NLB. A shared services account will host an API Gateway HTTP API to expose microservices privately. Access must be private (no public endpoints) and the company must control which internal entities can connect. The design must allow adding more microservices later. Which is the MOST secure solution that satisfies these requirements?

The correct solution uses AWS PrivateLink to establish private, secure, and scalable connections between the shared services account and each microservice account. A VPC endpoint service in each microservice account exposes the NLB privately. In the shared services account, a PrivateLink endpoint connects to these services. An ALB then targets the ENI IPs of these PrivateLink endpoints. API Gateway's VPC Link integrates with this ALB, ensuring private access without exposing microservices publicly. This design is secure, scalable, and allows easy addition of new microservices. Incorrect options: Connecting all VPCs via Transit Gateway and directly targeting NLB IPs in an ALB is less secure and scalable than PrivateLink, as it requires routing and exposes the NLBs more broadly. HTTP-based integration with Transit Gateway exposes internal NLB endpoints directly to API Gateway, which is less secure and manageable than using VPC Link and PrivateLink. Creating a separate VPC link to each NLB for each microservice, even with Transit Gateway, is less efficient and scalable than consolidating through an ALB fronting PrivateLink endpoints. VPC Links are typically associated with ALBs/NLBs, not directly with other NLBs as targets in this manner.