An application expects its license server at IP 10.0.3.21. To deploy the license server on Compute Engine without changing the application config and ensure reachability, what should you do?

The correct approach is to reserve 10.0.3.21 as a static internal IP and assign it to the license server VM. This ensures the license server always has the expected IP address, allowing the application to connect without modification. Static internal IPs are persistent and remain associated with your project until released. Reserving a static public IP is incorrect because the application expects an internal IP, and public IPs are for external access. Using a custom ephemeral IP is not possible; ephemeral IPs are assigned automatically from an available pool and cannot be custom-defined. Starting with an ephemeral IP and then promoting it to a static internal IP is not a valid operation for internal IPs; you reserve a specific internal IP and then assign it.