What is an event in the context of Event Driven Architecture?

An event is a notification that something significant has happened in the system. Events represent facts about what occurred and are typically immutable.

Key characteristics of events:

• Immutable: Once created, events cannot be changed
• Timestamped: Events have a timestamp indicating when they occurred
• Contextual: Events contain relevant data about what happened
• Past tense: Events describe something that has already happened

Example event structure:

{
  "eventId": "123e4567-e89b-12d3-a456-426614174000",
  "eventType": "OrderPlaced",
  "timestamp": "2024-01-15T10:30:00Z",
  "data": {
    "orderId": "ORD-001",
    "customerId": "CUST-456",
    "amount": 99.99
  }
}