Quarkus Multi Module Example

The goal of this project is to present a way to write a simple multi-module monolith.

Why multi-module monolith?

Because after I had the experience of developing in a big monolith ~400K LoC using the default technical layered architecture (controllers, service, mappers, model, repositories) I had some issues. The main issue was that I had to run the full app everytime, even when I only wanted to test 1 feature of a very small domain. This results in a slower startup and tests. Another issue was I had no clear division between domains

Don't get me wrong, I don't want to decouple domain and framework here (because I don't think it's worth it), I'm just saying that with a monolith I can't even see if a Banking domain change affects Contract domain because in the whole ball of mud, everything is together.

Architecture

I will use Maven module feature for this project and add some alternatives I considered in this README.md. If you don't know the basics of POM configuration, read my blogpost here: Configuring Maven POM

• billing: depends on user, example module.
• streaming: depends on user, example module.
• user: depends on nothing.
• application: centralize all modules in a single server.

With this project, you can run a single module or just run everything all at once. Just use maven commands

mvn -pl <module>

# e.g.
mvn -pl billing
mvn -pl application 

Database-per-module approach

Thanks to the beautiful Quarkus/Hibernate integration, it's a matter of updating the application.properties of each module and use Persistence Units:

# just follow the pattern
quarkus.datasource."module".property=

# e.g.
quarkus.datasource."billing".jdbc.url=source...
quarkus.datasource."billing".db-kind=postgresql
quarkus.hibernate-orm."billing".schema-management.strategy=update
quarkus.hibernate-orm."billing".datasource=billing
quarkus.hibernate-orm."billing".packages=com.joseiedo.billing

The app will even break if someone try to use entities of another persistence unit. Read more here

How to run?

1. Install Maven and Docker (it's used for the database connection).
2. Install modules to make them available in your local maven repository (necessary so other models can find each other):

mvn install

3. Play around.

mvn verify # You can see maven reactor showing all modules
mvn quarkus:dev -pl billing # will run only billing module
mvn quarkus:dev -pl application # will run application module

Notes

• Remember to run mvn install before building your native image/final jar of the application module to ensure all modules are in the maven repository.
• IDEs like intellij need to be configured. In the worst case, just use the terminal and create a Makefile to simplify everyone's life.
• Learn maven