A company's software development team needs an Amazon RDS Multi-AZ cluster. The RDS cluster will serve as a backend for a desktop client that is deployed on premises. The desktop client requires direct connectivity to the RDS cluster. The company must give the development team the ability to connect to the cluster by using the client when the team is in the office. Which solution provides the required connectivity MOST securely?

The most secure solution involves placing the RDS cluster in private subnets and using AWS Site-to-Site VPN. Private subnets ensure the database is not directly accessible from the internet, significantly reducing its attack surface. AWS Site-to-Site VPN creates a secure, encrypted tunnel between the company's on-premises network and the VPC, allowing desktop clients to connect directly and securely to the private RDS cluster. Placing the RDS cluster in public subnets (options 1 and 4) exposes it to the internet, which is less secure, even with a VPN or security groups. Using RDS security groups to allow office IP ranges directly (option 3) without a VPN is less secure than a VPN, as traffic would traverse the public internet unencrypted, and the database would still need to be in a public subnet or have a public IP for direct internet access.