This book is great if your main goal is to pass the unfortunately typical "systems design interview" in some companies (been there, done that). Also for "generic high-level knowledge" in that topic.

At the same time, there are several important "dangers" in the book: - For someone without the "proper mindset", it can easily lead to BDUF (Big Design Up Front) and a continuous violation of the YAGNI principle. Even if a couple of mentions to it are done throughout the book, they are far away from being enough and that should be warned continuously. - Some references/technologies are "too old" and there are better ones for some goals. - Some explanations are technically wrong (not sure if on purpose "for simplification purposes" or not). Unfortunately, I didn't write down which ones and I can't remember the details by heart :-/

Because of the previous points, IMO this is NOT a book for pure "self-improvement" and to take literally their ideas and implement them. 99 % of the systems implemented will never need to face the kind of scalability issues shown here. As Kent Beck said: "First, make it work. Then, make it right. Then, make it fast". And the fourth one that I add: "And finally, only if needed it: make it scale".