F5 - Closing And Opening Ports Solution

Answering inline:

1. We can create a service that will be enabled and disabled that runs in retrieval server and maybe F5 can connect on another port to check the status of that service in the retrieval server OR a service can connect from retrieval server to the F5 and enable the a service that will run in F5?

As long as there's something that the F5 can poll that will return the status of the server, you can use a monitor, and the port can be different than the actual pool members. I mentioned an external script, but depending on the complexity of the service you might be able to use the built-in monitors. Is the license service HTTP-based? If so it'd probably be easiest to just allow the F5 to do an HTTP GET or POST to a URL that provides that status. If you're actually enabling or disabling a Windows service (that's listening on a specific port), then you could probably use a TCP monitor.

1. Yes The second proposal might be the solutions since I can write an IControl script in C. And Please elaborate on that.

There are MANY examples of doing this in the iControl wiki, so I won't list anything here. The idea though is to create an iControl (via C, Python, PowerShell, etc.) that will launch on your defined event and either disable a pool member or enable it.