The readme at https://github.com/google/building-secure-and-reliable-systems/ https://github.com/google/building-secure-and-reliable-syste... does say this book

The readme at https://github.com/google/building-secure-and-reliable-systems/ https://github.com/google/building-secure-and-reliable-syste... does say this book is found there, and sure enough it's the first one on the list: https://google.github.io/building-secure-and-reliable-systems/ https://google.github.io/building-secure-and-reliable-system... It seems this github.io URL is more like a CI run of the book, and the one on sre.google is the "published" one.