Spring Modulith Implementation

• Spring Modulith Implementation
  • Data Setup
  • Learnings
  • How Spring Modulith Behaves when there are multiple instance of same application deployed (Without @Externalized )
  • After Using @Externalized annotation
  • How Spring Modulith Behaves when we have @Externalized event to kafka and also has one event listener in Application
  • Postman Collection for API's present in Project
  • Useful Commands
  • Reference
    • Comparison between Microservice ,Traditional Monolith and Modular Monolith

Data Setup

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1. Navigate to datasetup directory.
2. Run ./setupData.sh file.
3. After successful execution of step-2 it adds sample data.

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Learnings

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1. For each listener annotated with @ApplicationModuleListener/@TransactionalEventListener it created one entry in event_publication table
2. When we use simple @EventListener it doesn't create entry in event_publication table. it publishes event synchronously.
3. When we remove @Transactional from the method which is publishing the event then event is stored in event_publication table but not consumed by listener methods annotated with @ApplicationModuleListener/@TransactionalEventListener/@EventListener.

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How Spring Modulith Behaves when there are multiple instance of same application deployed (Without @Externalized )

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1. When instance 1 and instance 2 of applications are deployed together
2. The event published by instance 1 will be consumed by consumer in same instance 1
3. If instance 1 publishes the event, and before it is consumed by consumer if instance 1 terminated then event won't be consumed by instance 2's consumer.
4. If instance 1 publishes the event, and before it is consumed by consumer if instance 1 terminated then the new instance instance 3 that will be spin up can republish the outstanding messages if spring.modulith.republish-outstanding-events-on-restart=true property is enabled .
5. In order to handle republishing of outstanding events on demand we can use IncompleteEventPublications to resubmit outstanding events.

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After Using @Externalized annotation

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• With @Externalized annotation we can publish messages to various targets as given in spring modulith documentation.
• When @Externalized annotation is used and Modulith starts publishing events to Kafka. In order to see the published message on topic FoodOrderPlaced mention as target in @Externalized(target = "FoodOrderPlaced") event record. We can used below kafka console consumer command to consume kafka messages kafka-console-consumer --bootstrap-server localhost:29092 --topic FoodOrderPlaced --from-beginning

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How Spring Modulith Behaves when we have @Externalized event to kafka and also has one event listener in Application

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• It creates one event of type org.springframework.modulith.events.support.DelegatingEventExternalizer.externalize(java.lang.Object) for kafka and another event for event listener in Application in event_publication table

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Postman Collection for API's present in Project

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1. Navigate to Postman collection directory.
2. Import FoodDelivery.postman_collection.json file in postman.

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Useful Commands

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• To make container service up podman-compose up -d
• To make container service down podman-compose down

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Reference

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Comparison between Microservice ,Traditional Monolith and Modular Monolith

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