System Design Interview - An Insider's Guide, Second Edition

The first volume of Alex Xu's popular series (in its second edition). Each chapter is a standalone problem worked through using the same framework: clarify the requirements, make estimates, sketch a high-level design, then dig into the bottlenecks. Plenty of diagrams and very little fluff.

The book offers breadth rather than depth, so for individual topics it is worth following up with Designing Data-Intensive Applications. For interview preparation and a first introduction to the subject, it is one of the best.