Running Unity 'headless' on server - Same license?

I’m working on a game that requires some server side logic using unity, so I’m running unity in ‘headless’ mode on the server (eg. passing in -nographics command line argument). I’m a bit concerned however that this solution will not scale properly. It works fine right now because there is only one server, but if it blows up does that mean I need to buy a full copy of unity for every server machine? Those costs would quickly make the solution totally unfeasible. Has anyone else run into this problem?

Yes, you need one Unity license per machine. (Although you can have Unity installed on two machines, only one copy can run at a time.) What everyone else does is make an application using Unity that runs on the server.