Without any doubts I'll rate this book with 5 stars.
Background about me while reading this book: I've had some Rails background (still not an expert thought), and Docker basic knowledge (I could do some stuff with Docker, but it was rather because I got used to using them on the project, rather than seeking for a solutions myself). This was just enough to get my hands on the book and benefit from reading it. You won't get bored with all the stuff that is happening in the Docker's background (as it wouldn't even fit in a 200-page book) and that you would probably soon forget, instead the book is structured in a very reader-friendly way, focusing more on real action and it does not introduce to many new things in one chapter.
A friend described this book to be action-centered - and it really is. All of the things introduced in the book are based on a real (but rather simple) example, but I would agree with the author, that once you understand the pattern and the flow - you can use image of any external service and use it instead the ones presented in the examples. It's good to have such a script in front of you anyway, as in most of the cases you can just literally copy and paste the code present in the book to for instance get a redis or database service up and running within seconds (ok, minutes for first few tries)!
Another positive about this book is that you move in a well-known Rails commands and only adding Docker functionalities to it. That makes learning much easier, compared to watching/reading tutorials or books with a language you don't know, which all summed together makes you wonder if this is docker-specific option or just a feature of that language.
What really struck me, was that many of the commands and patterns shown in the book are present in real commercial projects all around the web, which means you are NOT learning just some academic stuff that no one uses :)
Docker is a really huge tool, the book does not cover all of the subjects, but you are not left alone - last chapter is filled with suggestions how you can develop you docker-skills further!
Second part of the book is devoted to a production environment, and it was not the purpose of me buying the book in my case, but it's also worth reading and understanding. But truth be told - based on what I've learned I wouldn't be able to set a proper, reliable and safe production env for a bigger app - but I was able to do so for a development environment (maybe just because the risk of a failure is smaller here, and in case something breaks you don't loose that much)
I'll add a warning though (author actually states that in the book, but many developers think otherwise) - Docker is not a solution for every single case. I've tried to introduce full Docker development environment in a project with a long history, and I must admit, that `alpha` version that I've prepared is not as performant as its `regular` sibling - but is still a great alternative for a people wanting to check something on their local machines without having to bother with all of the strange (and oftern stale and oooold) dependencies!