You don't learn to walk by following rules. You learn by doing, and by falling over.
The custom is to summarize the book at its end. I'll break that tradition by not writing a summary. We went through so many practices and tools that summarizing them would require quite a big chapter. After all, if, at this point, you need a summary of what you learned, it would only mean that you didn't learn as much as I hoped. Consequently, I would feel that I failed, get depressed, and never write another book.
The book was never meant to be a comprehensive cookbook. I haven't explained everything you can do with Docker. Nor I showed you all the power behind Ansible. As a matter a fact, I haven't gone into great details ...