A SaaS provider migrated a private SaaS app to AWS. Hundreds of customers connect from multiple data centers using VPNs and complex NAT rules. After migration, AWS-based customers must access the SaaS app directly from their VPCs, while on-premises customers must continue using IPsec tunnels. Which design satisfies these needs?

AWS PrivateLink is the most suitable solution for AWS customers as it provides private, secure, and direct access to the SaaS application from their VPCs without traversing the public internet. This simplifies networking and enhances security. For on-premises customers, terminating Site-to-Site VPN connections on a third-party routing appliance within the SaaS application VPC allows for centralized management of complex NAT rules and VPN configurations, which is often required for legacy on-premises setups. The other options are less ideal: Attaching AWS customer VPCs to a shared transit gateway would work for AWS customers, but it doesn't address the complex NAT rules for on-premises customers effectively, and managing hundreds of VPNs on a transit gateway can become complex. Peering each AWS customer's VPC with the SaaS application VPC creates a complex mesh network that is difficult to scale and manage. Terminating all VPNs on the SaaS VPC's virtual private gateway would also be difficult to scale and manage with hundreds of connections and complex NAT rules. Creating Site-to-Site VPN tunnels from each AWS customer's VPC to the SaaS application VPC is overly complex and expensive compared to PrivateLink, and doesn't scale well.