Add GNS3 appliance for NixOS

[ob7]

NixOS Appliance for GNS3

Overview

This GNS3 appliance enables dynamic hostname configuration for NixOS by passing the VM name to QEMU via -fw_cfg name=opt/vm_hostname,string=%vm-name%, then retrieving the value during NixOS initialization. A systemd job in the system's configuration.nix uses this value to override the hostname, providing clear and automated naming setups in lab environments. Users are encouraged to build their own qcow2 images using nixos-generators for further customization.

Purpose

• Dynamic Hostname: Automatically assigns the GNS3 instance name as the VM hostname for clear identification in lab setups.
• Custom Builds: Users can build their own qcow2 images with nixos-generators as outlined in this documentation.

Notes

• Tested on a bare-metal GNS3 server installation.
• Optional: Use nixos-generator to create custom images