The #1 book on their list is "Architecting for Scale" book by Lee Atchison. As the article says:
"The first one on our DevOps reading list is Architecting for Scale. It is an excellent book to understand real-world paradigms for scaling and managing critical applications. This book covers 5 different elements: availability, risk management, services and microservices, scaling applications and cloud services. This book can be called a practical guide as well, it shows how to prevent an application from becoming slow, inconsistent, or downright unavailable as it grows. Also, in this book the word “Scaling” is explained very well as it is not just about handling more users; it’s also about managing risk and ensuring availability."