This is possibly the most expert-level guide I've ever read to optimising your web servers.
Sysadmin experience required, and you'll want to have read all the other guides first, but if you have some servers you really need to squeak every last ms of speed out of (like, say, your tracking servers on $x,xxx / day campaigns), then this is pretty invaluable:
https://blogs.dropbox.com/tech/2017/...d-low-latency/
The Hacker News discussion on the post is also worth reading:
https://news.ycombinator.com/item?id=15185416