Recently, I’ve been studying some pretty cool architecture stuff, like onion and hexagonal architecture, then, I stumbled into this awesome talk from Matthias Noback at PHP Barcelona Conference in 2015, which I’d strongly recommend to you to deepen your knowledge on this subject. Due to my PHP background, it has been proved as a precious content.
Another great resource to improve your understanding of architecture is this hangout of BoldRadius, even though isn’t focused on a particular language the host doesn’t hide your Scala background, he uses a bowling system as a sample, in a precise and well-described way to introduce the concept.
In both videos, you will able to see how Onion and Hexagonal architecture are almost intrinsically involved with DDD, although you may have one without other. I’m still a beginner in it, but I hope that it may be as useful as it was for me.