https://reflectoring.io/book/
A good software architecture should keep the cost of development low over the complete lifetime of an application.
Ever wondered about how to actually implement a “Clean Architecture” or a “Hexagonal Architecture”? There’s a lot of noise around these keywords, but you can find very little hands-on material on this topic.
This book fills a void by providing a hands-on approach to the Hexagonal architecture style from the concepts behind it down to actual code.

- e-book only (101-page PDF, .mobi, and .epub)
- support me directly by paying more than the minimum price
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- get updated versions immediately and for free

All About Hexagonal Architecture
- learn the concepts behind "Clean Architecture" and "Hexagonal Architecture"
- explore a hands-on approach of implementing a Hexagonal architecture with example code on GitHub
- develop your domain code independent of database or web concerns

Get a Grip on Your Layers
- learn about potential problems of the common layered architecture style
- free your domain layer of oppressive dependencies using dependency inversion
- structure your code in an architecturally expressive way