Microservice - Project folder structure for hexagonal architecture

grpc.go is for defining the handlers, and server.go mostly runs the server and register endpoints inside the grpc.go file.

While there are no written rules for a hexagonal architecture folder, the following folders are common in typical Go projects:
 Application folder—This folder contains microservice business logic, which is a combination of the domain model that refers to a business entity and an API that exposes core functionalities to other modules.
 Port folder—This folder contains contract information for integration between the core application and third parties. This can be a contract about accessing core application features or about specifying available features for a database system, if one is used for the persistence layer.
 Adapter folder—This folder contains concrete implementation for using contracts that are defined in ports. For example, gRPC can be an adapter with a concrete implementation that handles requests and uses an API port to access core functionalities, such as if you have an application with some functionalities and will expose it to customers. The functionalities can be CreateProduct, GetProduct, and so on, and you can expose them to the customer via REST, gRPC, and other adaptors, which will use the contracts of those functionalities, as defined in the port layer. 

 

Application, port, and adapter folders can be located inside an internal folder to separate operational functionalities, such as infra and deployment from application core logic. A cmd folder can also define an application’s entry point, which also contains dependency injection mechanisms, such as preparing a database connection and passing it to the application layer. Finally, there can be utility folders, such as config, to provide a configuration structure so that consumers will know the possible parameters they can pass while running the application.