The project structure, in this case, will be almost the same as we had before.

We'll have an API layer responsible for the interaction with HTTP clients. We'll also inevitably have some configuration and a database initialization code that will be implemented in a similar, or identical, way to what we did as we've built the previous microservice.

The persistence layer will be represented by a persistent actor. This will affect the definition of the model as well as the structure of the database tables. 

Akka Persistence introduces different paradigms of how the state of the system is stored and represented. The approach is called Event-Sourcing and it makes sense to take a minute to discuss it.