Whenever I think of WebSockets/real-time I think of Socket.io but I would be interested to hear a response from the Socket.IO team in regards to Trello saying [0] they couldn't scale Socket.IO over 10K connections:<p>> We use a modified version* of the Socket.io client and server libraries that allows us to keep many thousands of open WebSockets on each of our servers at very little cost in terms of CPU or memory usage.<p>> * The Socket.io server currently has some problems with scaling up to more than 10K simultaneous client connections when using multiple processes and the Redis store, and the client has some issues that can cause it to open multiple connections to the same server, or not know that its connection has been severed. There are some issues with submitting our fixes (hacks!) back to the project – in many cases they only work with WebSockets (the only Socket.io transport we use). We are working to get those changes which are fit for general consumption ready to submit back to the project.<p>I'd be interested to hear if those "hacks" got merged in or fixed some other way. Of course most of us aren't dealing with 10K simultaneous connections and Socket.IO is awesome so this is in no way a warning to keep away from it, I'm just interested.<p>[0] <a href="http://blog.fogcreek.com/the-trello-tech-stack/#asterisk" rel="nofollow">http://blog.fogcreek.com/the-trello-tech-stack/#asterisk</a>