Spring Boot Moduliths

🧚 The fairy tale of a growing application

Medimind Once upon a time, there was a small application… User Inventory Medication

Medimind Each sprint, the application grew… User Inventory Medication Shedule

Medimind And grew… User Inventory Medication Schedule

Medimind And grew even more… User Inventory Medication Schedule Prescription

Medimind Eventually nobody understood the application… User Inventory Medication Schedule Prescription Notification

Notification Microservice Prescription Microservice Schedule Microservice Medication Microservice User Microservice Inventory Microservice Until one day, the Architect Wizard™ arrived, and transformed it into microservices…. User Inventory Medication Schedule Notification Prescription Mediminder gateway Event bus

Notification Microservice Prescription Microservice Schedule Microservice Medication Microservice User Microservice Inventory Microservice Peace returned, until one day a microservice caught fire… User Inventory Medication Schedule Notification Prescription Mediminder gateway Event bus ❌ ❌

Notification Microservice Prescription Microservice Schedule Microservice Medication Microservice User Microservice Inventory Microservice The fire spread… User Inventory Medication Schedule Notification Prescription Mediminder gateway Event bus ❌ ❌ ❌ ❌ ❌ ❌ ❌ ❌

Notification Microservice Prescription Microservice Schedule Microservice Medication Microservice User Microservice Inventory Microservice The DevOps Heroes™ quickly restarted the microservice… User Inventory Medication Schedule Notification Prescription Mediminder gateway Event bus

Notification Microservice Prescription Microservice Schedule Microservice Medication Microservice User Microservice Inventory Microservice And added extra infrastructure to prevent future problems User Inventory Medication Schedule Notification Prescription Mediminder gateway Event bus

The end … ?

What did we learn? ● High coupling is evil ● Microservices can help ● Extra resources ● Extra code ● Less focus on business code

🤔 Is there an alternative?

Medimind Modular monoliths User Inventory Medication Schedule Prescription Notification Spring Data Events

Spring Data Events? @Entity // Extend from AbstractAggregateRoot public class Schedule extends AbstractAggregateRoot { @OneToMany private List completedEvents; public void addCompletedEvent(LocalDate eventDate) { this.completedEvents.add(CompletedEvent.of(this, eventDate)); // Call registerEvent() registerEvent(MedicationTakenEvent.of(this, eventDate)); } }

Spring Data Events? @Component @RequiredArgsConstructor public class MedicationTakenEventListener { private final InventoryFacade facade; @TransactionalEventListener(phase = TransactionPhase.BEFORE_COMMIT) public void subtractFromInventory(MedicationTakenEvent event) { facade.removeQuantity(event.userId(), event.medicationId(), event.quantity()); } }

How to prevent high coupling? ● Java access modifiers ● Java modules ● Moduliths

Meet Moduliths /ˈmɑːd ͡ ʒəlɪθ/ Speciaal voor Kenneth in het fonetische schrift

Add some dependencies… org.moduliths moduliths-core org.moduliths moduliths-test test

Structure your code… 1. Create a new package for each module

Structure your code… 2. Put exposed classes in a module package 1. Create a new package for each module

Structure your code… 3. Put implementation details in a subpackage 2. Put exposed classes in a module package 1. Create a new package for each module

… And write a test @ModuleTest public class InventoryModuleTest { @Test void moduleLoads() { } }

… And write a test

Pro’s & Con’s ● Developed by Spring Data lead ● Favours conventions over configuration ● Easy integration with Spring Boot ● Only bootstraps module during tests ● Small community ● Does not replace microservices

Resources ● https://moduliths.org/ ● https://www.youtube.com/watch?v=bVaiTPYlHFE ● https://github.com/g00glen00b/medication-assistant ● https://speakerdeck.com/g00glen00b/tech-talk-moduliths

🙏 Thank you for listening!