System Design Interview Mastery

System Design Interview Mastery is a structured framework for engineers preparing for senior, staff, and principal-level system design interviews - the evaluations where a blank whiteboard and an open-ended prompt determine the outcome of months of preparation.Rather than cataloging solutions to memorize, this book teaches a repeatable process for reasoning through ambiguity: a five-step framework for turning a vague prompt into a scoped engineering problem, a decision lens for choosing deliberately between the databases, caches, queues, and infrastructure components common to nearly every design problem, and a complete toolkit for scaling systems from a single server to resilient, multi-region infrastructure.Beyond frameworks, the book addresses execution - leading a technical conversation, handling pushback and shifting constraints, and recovering credibly when a gap in knowledge surfaces mid-interview. It closes with a full case study: a real-time event ticketing platform under flash-sale load, presented first as a 45-minute annotated mock interview, then as an extended technical deep-dive connecting every decision back to the frameworks taught throughout the book.Grounded in real interviews and real systems rather than theory, this is a book meant to be practiced with, not simply read - written for engineers who want to walk into any design conversation and lead it with clarity, structure, and confidence.