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Refine the answer for “What key elements are part of EDA (publisher, subscriber, event bus)?”. Your changes go to moderation before they’re published.

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Event-driven architecture (**EDA**) has three key elements that handle the transmission and processing of events:

### 1. **Publisher**

A component that **creates and sends an event** when the state changes.
It does not know who will receive the event, it just publishes the fact:

> "Payment completed", "New order created".

*Example:* the orders service publishes `OrderCreated` after creating an order.

### 2. **Event Bus / Message Broker**

An intermediate layer that accepts, stores, and delivers events to subscribers.
It provides reliability, routing, and scalability.

*Example tools:*
**Apache Kafka**, **RabbitMQ**, **NATS**, **ActiveMQ**, **AWS SNS/SQS**.

Functions:

- routing events by topic,
- buffering during load spikes,
- guaranteed delivery.

### 3. **Subscriber / Consumer**

A component that **subscribes to events** and reacts to them.
It can:

- update its own data,
- trigger internal business logic,
- generate new events.

*Example:* the notification service is subscribed to `OrderCreated` and sends the customer a confirmation email.

### Overall scheme

```javascript
Publisher → Event Bus → Subscriber
```

1. The publisher publishes an event.
2. The event bus delivers it to all subscribers.
3. Each subscriber processes the event independently.

**Conclusion:**

> The key elements of EDA are the **Publisher**, the **Event Bus**, and the **Subscriber**.
> Together they create a flexible, asynchronous ecosystem where services communicate not directly, but through a stream of events.

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