Microsoft also published a good series of articles on DDD / CQRS / Hexagonal architectures [1]. I especially like the diagrams of dependencies between layers on that linked page.
I prefer to have an additional layer that is usually called the service layer. You use it to express and orchestrate the actions of your application without hard dependencies on specific tech.
So the application layer is the one that manages specific dependencies and injects them into the service layer and the service layer then goes:
- okay, when asked to disburse a loan
- I construct a domain object for the loan
- If the object is valid, I make a sync call to deposit the money
- I then persist the loan
- I then send a notification that a loan is disbursed
And it doesn't really know how the RPC, the notification, or the persistence layer actually work.
[1] https://docs.microsoft.com/en-us/dotnet/architecture/microse...