Controller: auto-discover server after nethsecurity-controller restoration

[stephdl]

Issue Description:

During a backup restoration process that involves replacing the nethsecurity-controller module, the connection between the controller and the nethsecurity instance is lost. This happens because the TCP ports differ between the old and new modules. Once the restoration is complete, the ns8 module operates normally, but the nethsecurity instance becomes unreachable and is not visible in the system.

To resolve this, manual intervention is currently required: you need to access the nethsecurity instance and manually restart the ns-plug service.

Proposed Improvement (NFR):

Develop a solution that ensures the connection between nethsecurity and the ns8 controller is automatically restored after a backup restoration, eliminating the need for manual intervention.

Steps to Reproduce:

1. Install and configure a nethsecurity instance.
2. Install and configure a nethsecurity-controller to link with the nethsecurity instance.
3. Perform a backup of the setup.
4. Restore the backup.
5. Observe that the nethsecurity instance is not visible or online in the nethsecurity-controller.
6. Manually restart the connection by navigating to the nethsecurity system > controller menu and restarting the ns-plug service.
7. After restarting, the nethsecurity and ns8 controller can communicate successfully.

Proposed Solution:

The connection between the instances is established via an OpenVPN tunnel (tun-nsplug). When the tunnel goes down, a trigger could automatically restart the ns-plug service. The downside is that the service has a 60-second timeout period for attempts before it stops.

Alternative Solutions:

Implement a cron job that monitors the connection status. If the tunnel goes down due to a lack of connectivity, the job can automatically restart the ns-plug service.
This enhancement aims to make the restoration process more seamless and reliable.