# Event Message

> Something happened — broadcast it. Subscribers react however they want.

- **Category**: Integration
- **Subcategory**: Message Construction
- **Canonical URL**: https://designpattern.fyi/patterns/event_message/

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## Description
Clean, reusable architecture pattern.


## Use Cases
User completes checkout → OrderPlaced event published to Kafka topic. Inventory Service decrements stock. Shipping Service creates a shipment. Email Service sends confirmation. All from the same single event, zero coupling to the publisher.





## Trade-offs


### Advantages

- Zero coupling — publisher never knows its consumers

- New consumers can be added with zero changes to the publisher

- Natural backbone for event-driven architecture

- Perfect audit trail — events are facts, immutable by nature




### Considerations & Drawbacks

- No guaranteed delivery without durable subscriptions and persistent brokers

- Eventual consistency — consumers lag behind the event

- Event schema changes need backward compatibility management

- Hard to trace end-to-end flow without distributed tracing (Zipkin, Jaeger)







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**Reference**: [Original Source](https://www.enterpriseintegrationpatterns.com/patterns/messaging/EventMessage.html)