There is a good discussion on how to configure a reverse VPN tunnelling. Look like connecting back to the system is complicated issue. The essence of your problem is that even you can do the DNS registration (which makes eligible for the servers to find each other), the actual ip connection between your machines is further impossible.

Please advice on which rule has been violated and what else should be done. [Edit] My bad! I see there is WCF group under general programming! Sorry!

One way to make it generic and easy adaptable is: Extend the .Net FileWatcher class and create a component that listens to certain file changes in a directory. Next Create a windows Service application that will use this component. The settings and number of instances can be made configurable through the app config file of your windows service application. When a Instance notices a file change write a message to the application log file of the windows event Log. Using the Windows Event viewer You then can create custom views that filter for your messages generated by your Windows service application. On each custom view you can attach a task that will be triggered each time a message is written. To this task you can attach a batch file, powershell script or VBScript that will execute and perform your needed functionality each time the task is triggered.