Amazon EventBridge

Amazon EventBridge is a serverless event bus that connects applications using events. While SNS provides pub/sub messaging and SQS provides point-to-point queuing, EventBridge adds intelligent event routing with content-based rules, schema discovery, and native integration with over 200 AWS services and third-party SaaS applications.

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What Is EventBridge?

EventBridge is an event bus — a central hub that receives events from many sources and routes them to targets based on rules you define. Think of it as a smart switchboard that examines each incoming event and decides where to send it.

[Source A] ——>                          ——> [Target 1: Lambda]
[Source B] ——>  [EventBridge Event Bus]  ——> [Target 2: SQS]
[Source C] ——>                          ——> [Target 3: Step Functions]

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EventBridge vs SNS: When to Use Which

Feature	SNS	EventBridge
Routing	Filter policies on subscriptions	Content-based rules on event body
Event sources	Your applications	AWS services, SaaS apps, your applications
Schema	No schema enforcement	Schema registry and discovery
Targets	SQS, Lambda, HTTP, Email, SMS	20+ target types including Step Functions, API Gateway, other buses
Throughput	Nearly unlimited	Region-dependent (soft limit, can be increased)
Archive and replay	Not supported	Built-in event archive and replay
Cross-account	Via topic policies	Via cross-account event buses
Best for	Simple pub/sub, high throughput	Complex routing, AWS service events, SaaS integration

Rule of thumb: Use SNS for simple, high-throughput fan-out. Use EventBridge for complex event routing, when you need to react to AWS service events, or when you need schema management.

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Core Concepts

Event Bus

An event bus receives events. Every AWS account has a default event bus that automatically receives events from AWS services. You can also create custom event buses for your own applications.

Bus Type	Source	Use Case
Default	AWS services	React to EC2 state changes, S3 events, etc.
Custom	Your applications	Domain events for your microservices
Partner	SaaS applications	Events from Zendesk, Datadog, Auth0, etc.

Events

An EventBridge event is a JSON object with a specific structure:

{
  "version": "0",
  "id": "abc123-def456",
  "source": "order-service",
  "detail-type": "OrderPlaced",
  "time": "2025-03-15T10:30:00Z",
  "region": "eu-west-2",
  "account": "123456789012",
  "detail": {
    "orderId": "ORD-12345",
    "customerId": "CUST-789",
    "total": 149.99,
    "items": ["SKU-001", "SKU-042"]
  }
}

Key fields:

Field	Description
source	Identifies who produced the event
detail-type	The type of event (like an event name)
detail	The event payload — your custom data
time	When the event occurred

Rules

Rules match incoming events and route them to targets. A rule consists of:

1. Event pattern — which events to match
2. Targets — where to send matching events (up to 5 targets per rule)

Targets

A target is a resource that receives the event. EventBridge supports over 20 target types: