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Well written, clear, and enlightening. This is absolutely required reading for anyone doing web development (front and back).
If you can, buy a hard copy to keep as a reference. I have referred back to mine regularly (and will surely refer back to it in the future, likely next time I have to do something serious with websockets). It's fairly neatly organized by protocol, so if you just need a quick review of HTTP2 (for example), you can skip to that section and read it in isolation.
I highly, highly recommend.
-- this book, about NAT