Comment by Matheus28

Their approach is quite simple and effective, it is what I suggest game developers do. For reference, it goes somewhat like this:

The clients connect to a relay server that just forwards the packets back and forth between the client and the real server. The client never gets to know the real server IP, preventing attackers from DDoSing the servers. If the connection to the relay server drops (which can easily happen if the attacker DDoSes the relay server instead), it can easily resume the connection with any other relay server, and the real server never notices it dropped.

This relies on the fact that there are too many relay servers to DDoS at once, and attackers never get to know the real server running the game code, so they can't make it unreachable.