There are multiple questions about what this book is about, who it's for and what might be relevant for me. We recommend going through the Preface to get answers to these questions. Copy/pasting a few paragraphs:
"In this book we talk generally about systems, which is a conceptual way of thinking about the groups of components that cooperate to perform some function.
We wanted to write a book that focuses on integrating security and reliability directly into the software and system lifecycle, both to highlight technologies and practices that protect systems and keep them reliable, and to illustrate how those practices
interact with each other.
We’d like to explicitly acknowledge that some of the strategies this book recommends require infrastructure support that simply may not exist where you’re currently working.
Because security and reliability are everyone’s responsibility, we’re targeting a broad
audience: people who design, implement, and maintain systems. We’re challenging the dividing lines between the traditional professional roles of developers, architects, SREs, systems administrators, and security engineers.
Building and adopting the widespread best practices we recommend in this book requires a culture that is supportive of such change. We feel it is essential that you address the culture of your organization in parallel with the technology choices you
make to focus on both security and reliability, so that any adjustments you make are persistent and resilient.
We recommend you start with Chapters 1 and 2, and then read the chapters that most interest you. Most chapters begin with a boxed preface or executive summary
that outlines the following:
• The problem statement
• When in the software development lifecycle you should apply these principles and practices
• The intersections of and/or tradeoffs between reliability and security to consider
Within each chapter, topics are generally ordered from the most fundamental to the most sophisticated. We also call out deep dives and specialized subjects with an alligator icon."