I will use for it the Ubuntu LTS desktop template we have with full KDE.
Go to add instance, select the Ubuntu Desktop template, proceed like above and make sure you select the network we created before and the same group, otherwise the new VM will be in a different VLAN and will not be able to communicate with the debian server we made before over the internal network.
Write down password and use the console to login to your desktop:
Since we already allowed external access to the network and this VM uses the same VLAN, we no longer need to do anything, our desktop will be able to browse the internet, for example:
Now we will allow VNC access to the desktop.
We will need to enable Desktop Sharing in KDE (in applications, internet) to allow uninvited connections. You may or may not change the default port, it can be done both there or in the firewall, let's say we leave it default (5900) and change it in the firewall.
In the firewall open port 3003 and forward it to port 5900:
Make sure you select the right VM to which to forward the port, it is the ubuntu desktop, not the debian server.
And now you can use VNC to control your Ubuntu Desktop from home. You will use as address in your VNC viewer something like xxx.xxx.xxx.xxx:3003 where xxx.xxx.xxx.xxx is your IP and 3003 is the port we choose. You can put another, but make sure you adapt the firewall rules to match. If you do not wish to specify any port, you can use the default 5900.
Alternatively, you can install RDP and use that to control your Ubuntu Desktop, but again, your ports will be different. ou can also enable ssh, naturally, not ont he same port as before, in fact none of the ports can be reused, so, if you forwarded 222 to 22 on your debian server, you cannot use the same configuration, you need to forward another port, say 2222 to your Ubuntu's 22 port.
Once you can control a desktop inside the lan, everything is simple, youw ill be able to connect to debian server using the ssh client in Ubuntu, just this time is port 22 because you are already inside the LAN, no need for any forwarding. You will issue the command:
to connect to your debian server in this case, that is the LAN IP of your debian server, you can always find it out issuing the ifconfig command.
Something like this:
You can add more servers and workstations as long as you have the necessary resources (memory, disk space, CPUs) effectively simulating an entire lan inside with all the required stuff, from storage servers to web/email/ftp/application servers, etc. you can even load own ISO and install windows, free bsd, whatever, just be advised that without using the templates, the password reset function will not work.