What determines a server's or LAMP stack's max concurrent users?

I'm looking to build my own server for the fun of it and in order to learn about the process.

I will be setting up a LAMP stack on the server and use it as a back-end for my mobile application that has some 1000s of daily active users.

But I am completely clueless as to what determines the limits of my server. I see on many hosting providers' websites that they offer a fixed amount of concurrent users, like 20 or 100.

What are the reasons that determine the maximum number of concurrent users for a server? Is it just dependent on the server's hardware, like available RAM? Does it have to do with code or software? What happens to users who try to access the server when the maximum limit has already been reached?

https://stackoverflow.com/questions/66927704/what-determines-a-servers-or-lamp-stacks-max-concurrent-users April 03, 2021 at 12:21PM