Online RPG Games

Hello everybody. I’m a programmer and I downloaded “Lumberyard” today “Lumberyard” for the first time. I’m writing here because I would like to approach the study about multiplayer video games, server structure and so on. I made code for a framework of a famouse MMORPG where it use Opcode to exchange data (over a TCP socekt) between client and server and a simply MySQL DB to store data. Now, my question is: this approach is still used? Is there a book that speaks about the frameworks used for this?
Thanks in advice.