Where to learn about server/balance loader concepts?

During my interviews, often times I got asked questions about server, apache, balance loader, web socket and etc. Though I have experience with deploying apps on heroku, I’ve no idea about these concepts (except for socket.io for web socket). Anyone can recommend a course/book about these topics? I tried to google around, but I’m still confused after watching multiple YouTube videos.

I would recommend starting by reading over some HTTP tutorials and then moving into reading about servers and how requests are handled. There is enough basic theory in web servers to fill books, however there are good tutorials out there too. Digital Ocean posts good tutorials on server configuration and load balancing.

I think you’ll need to spend some time looking at the high level theory and then move to specific application configuration.