I look forward to the day when more and more PHP developers adopt Domain-Driven Design (DDD). The current sentiment is that it is hard to implement and maintain. There is some truth to that, but I think it is only true due to a lack of trying. Things become less difficult when we truly put our minds to learning and testing it.
When I first learned about DDD, its concept made total sense to me, even though it took me a while to understand it. I am still learning.
Here are 5 online resources that will help you get a better understanding of Domain-Driven Design (DDD):
Domain-Driven Design with PHP - This is an introductory article to DDD by Stefan Priebsch. You can also find some of his talks on YouTube where he discusses other topics such as Event Sourcing and Software Architecture.
Domain-Driven Design in PHP - This is a book worth owning. I've read through it several times, and it offers many examples so that you can understand how to do DDD in PHP and how each part works together.
Matthias Noback - I would love to sit with Matthias and pick his brain. He is knowledgeable in DDD, ORM, software architecture, and many other web development topics. His blog is a wealth of information even beyond DDD.
An Introduction to Domain Driven Design | PHP Sussex - Rob Allen's talk on DDD is a good one to watch and listen to on repeat.
CodefyPHP Documentation - Codefy is a simple, light framework providing interfaces and implementations for architecting a Domain-Driven project with CQRS and Event Sourcing. The documentation can help with understanding DDD and how it can be implemented.