Setting BIG-IP LTM Virtual Server for two SQL Servers nodes

The IP in the Virtual Server destination field will be a private address from AWS on the "external" interface. You'll then assign an Elastic IP to that address if you need public access to the Virtual Server. The port you pick on the service port isn't important as long as the UDL file is configured to match. The UDL will need to specify the Elastic IP instead of the private address if you are connecting over the internet to the virtual server.