I've built an application with node and socket.io to keep track when a visitor visits a page, and leaves. When the visitor leaves I store the time the visitor was on the page to redis. That's all the application has to do.
Here's the thing, the application needs to support ~15k concurrent connections, but I'm getting a lot of handshake errors when the benchmark hits around 10.000 conc. visitors. I don't know why exactly. Does anyone have any experience with these kind of problems?
I also tried scaling the application in multiple processes, using the RedisStore backend for node but haven't had much success.
There are a number of things which could be causing this. You should check your system error logs and see if there are any errors there which may indicate where the problem actually is.
This question has some good information and the limit they were hitting is close to what you are hitting as well. It's worth a look.