So I've never made an MMO before, but I know some of you guys have worked on them! I have been studying netcode.io and wanted to ask if anyone here had opinions or insights on why netcode would not be a very good fit for huge MMO style games.
In case anyone is not familiar, netcode was mostly designed for games with around 2-64 players or so, like FPS games or agar.io style games, and uses UDP. It has a well designed secure connection authentication system, using opaque connect tokens derived by piggy-backing off of a secure HTTPS REST call to a webserver authenticator. Once a token is obtained by the client by making a REST call, they hand an encrypted section of the token to a dedicated server and begin the connection handshake with a secret keyset obtained from the webserver over HTTPS. It's all actually quite simple, and documented in the netcode standard. To me, this is the most appealing feature of netcode and libyojimbo (libyojimbo is a C++ wrapper around netcode that also adds in HTTPS support, basic matchmaking, and reliability features).
For context, say we are talking about an MMO where anywhere from 2-3000 players can reside within an active instance of the game on a single server. This figure can be thought of as the peak capacity for any of the MMO dedicated servers. The gameplay typically looks like Oldschool Runescape - lots of click and watch the player slowly walk to the click point. Event/RPC style programming would be pretty typical, and over TCP would work just fine traditionally. In the case of netcode, the reference implementation keeps a pre-allocated array of client instances. A quick test shows all pre-allocated data comes out to just ~30MB for 3000 players, for one dedicated server instance, which is really quite small (this figure is just describing the memory cost on the protocol level, not the per-client memory cost of the actual game simulation).
netcode has some tuning parameters for connection timeouts and packet send rates, which are ten times per second. If these are too high for an MMO, this can be tuned.
Of course, netcode itself does not handle packet reliability. However, netcode can be wrapped with a reliability implementation (like libyojimbo), so let us assume the reliability adds another 30-100 MB at peak server capacity, totaling to around 100-150MB for the server instance when no packets are in flight. Of course, when packets are in flight, memory consumption goes up as packets get buffered. I'm not sure how much, but let us assume a gigabyte of RAM should be reserved for packet traffic and the server protocol instance itself, along with all clients. This could leave ~4-6 GB of space to run the instance on a device with around ~8 GB of RAM total.
Okay, that's probably enough context. With this kind of story, in your experience what are the key requirements for an MMO that netcode might miss? Are there any other unfavorable aspects of netcode that would prevent it from being a good MMO option?
Here was the only point I could think of: netcode's default implementation pulls packets off of the UDP stack only via polling. Instead, I think a single dedicated thread could be used to read off of the UDP socket, and queue packets up. The queue could be polled by the user calling into netcode. This can prevent the UDP stack buffer from filling up and causing packet loss.
