Books / manuals on the implementation of the server for the game client on Unity3d?

Question

C++ / C#

There was a desire to create a server for my game.
I have been communicating with Unity3d for more than a year, I periodically create casual games for my circle.
Suddenly I wanted to create an online/multiplayer game.
It dawned on me that there is no experience with the network (residual knowledge after the university does not count).
Googling found 3 implementation options.
1) Write your own server with pens (server flexibility)
2) Use ready-made solutions (there are restrictions, for a fee)
3) Use the tools of the client-server of Unity3d itself (quite resource-intensive)
I stopped at this and write here.
I'm most interested in the first option.
Tell me books / manuals on the network and server implementation (general scheme or specifically for Unity). Personal experience is also welcome.
Preferred Language C#

Answer 1

Search for the keywords " C# REST Services " or " C# Web API "
There is something else on Habré.
But in general, you will most likely not find free hosting under C# (suddenly this is a problem).
I would try Ruby if I know the language and I need it for free.
If free is not needed, then ASP.Net MVC or even Web API