I'm working on a browser game, that does all communication to the game server through WebSockets.

Here I have the clients ping the server every 2 seconds, and if I haven't received a message with in 10 seconds (including other messages than ping) I consider the client dead.

Each socket is assigned to an individual player, and if that player opens a second connections the old one dies.

To be honest - In regards to the missed messages and order of events, I just cross my fingers and hope TCP does that for me.

In regards to the clustering, I have my map split up into sections, so most of the messages that needs to be send, are only to the people in that sector. So I rarely send a message to all players.

I'm still experimenting, so I'll probably still have a lot of edge cases that I'll have to cover. But for now it seem to work well.