The premise is that people don't understand their system, or software, and need to be told how it works. So you have an admittedly ignorant person telling other ignorant persons that there are possibilities out there. That's... not really useful.

What is useful is to spend 2 days researching massively concurrent network applications, and find the ones that were already written, and see how they evolved over time. For the most part, it's just understanding your operating system and network protocols. Once you learn how they all work, the answers come quickly. This problem has been solved many times.

But for the most part, none of you need to know how this stuff works. You can write the crappiest network server in the world, and there are still so many other components you can wrap around it to make it scale that you never even need to get close to network optimization. So you may have to run 10 instances of your app; who cares? We have virtually unlimited everything these days. The answer to a poorly performing app is "just throw more cloud at it".

Also, I feel the need to remind everyone that single app instance handling 100K+ concurrent connections is a terrible fucking idea. What happens when the app crashes? What happens when the hardware dies? What happens when you need to, like, upgrade/restart the app? Several million SYN packets in 100ms, and default kernel TIME_WAIT settings, do not make great bedfellows.