In our application, we had a single project that defined multiple sub-projects, so a single project contained definitions and implementations of all our microservices. This has a few advantages—it is much easier to include the Lagom Service API's definitions of a microservice as dependencies with other microservices.
However, if there are more people working on the same project, then it can become tedious for multiple developers. In which case, each microservice can be a separate independent SBT project of its own. However, the service-api definition's JARs would need to be uploaded to a Maven repository and shared with other teams.
With Lagom, you can take any approach. You can start with a single project approach and later split it to multiple projects if the need arises. If you split your application into multiple builds, the following...