Q: Your SaaS company provides a database-as-a-service. A massive banking client wants to securely connect to your database from their AWS VPC. Their strict compliance prohibits traversing the public internet, and prohibits VPC Peering because they refuse to expose their internal routing tables to you. How do you architect the connection?

This is the exact use case for AWS PrivateLink (VPC Endpoint Services).

• In your SaaS VPC, you place a Network Load Balancer (NLB) in front of the database and expose it as a VPC Endpoint Service.
• The banking client requests to connect to your service. Upon your explicit approval, they create a VPC Interface Endpoint inside their own VPC.
• This creates Elastic Network Interfaces (ENIs) natively inside the bank's subnets.

The bank's applications communicate with these local ENIs using local private IPs. AWS PrivateLink securely pipes that traffic directly to your SaaS NLB under the hood over the AWS internal backbone. Why it passes audit: Unlike VPC Peering, PrivateLink is purely uni-directional. The bank can initiate requests to you, but it is physically impossible for your SaaS network to initiate a reverse connection back into the bank's internal network to scan or attack them.