Module 5: Using EventBridge and SNS to Decouple Components

Module Overview

This module covers asynchronous event-driven patterns using Amazon EventBridge and Amazon SNS to build loosely coupled serverless architectures.

Topics

• Asynchronous event sources for Lambda
• Amazon EventBridge as a serverless event bus
• Amazon SNS as pub/sub messaging
• Event filtering and routing
• When to use EventBridge vs SNS

1. Asynchronous Event Processing

In async invocation, the caller doesn't wait for the function to finish. Lambda queues the event and processes it independently.

Sync vs Async Invocation

Async Flow

Notifying the Client (Async Patterns)

2. Amazon EventBridge

A serverless event bus that connects applications using events from AWS services, SaaS apps, and custom sources.

Key Concepts

Event Structure

{
  "version": "0",
  "id": "12345678-1234-1234-1234-123456789012",
  "source": "com.mycompany.orders",
  "detail-type": "Order Created",
  "account": "123456789012",
  "time": "2024-06-15T10:30:00Z",
  "region": "us-west-2",
  "detail": {
    "orderId": "ORD-987654",
    "department": "billing",
    "amount": 149.99,
    "customer": "user12345"
  }
}

Event Pattern (Rule Filter)

// Match orders from billing or fulfillment departments
{
  "source": ["com.mycompany.orders"],
  "detail-type": ["Order Created"],
  "detail": {
    "department": ["billing", "fulfillment"]
  }
}

EventBridge Targets (20+ supported)

Lambda | SQS | SNS | Step Functions | Kinesis | API Gateway | CloudWatch Logs | CodePipeline | ECS Task | Redshift | API Destinations (any HTTP endpoint) | Another Event Bus (cross-account/region)

3. Amazon SNS (Simple Notification Service)

Fully managed pub/sub messaging service for fan-out to multiple subscribers.

Key Concepts

SNS Message Filtering

Filter Policy Example

// Subscription filter policy - only receive "billing" department messages
{
  "department": ["billing"],
  "amount": [{"numeric": [">=", 100]}]
}

Nested Serverless Applications (Fan-out Pattern)

One SNS topic can fan-out to multiple independent microservices (search indexing, backup, analytics, notifications) - each runs independently and can fail without affecting others.

4. EventBridge vs Amazon SNS

When to Use What

5. Live Demo: EventBridge Rule + Lambda Target

Step 1: Create a custom event bus

aws events create-event-bus --name demo-orders-bus --region us-west-2

Step 2: Create a Lambda function (target)

# handler.py
import json

def handler(event, context):
    print(f"Received event: {json.dumps(event)}")
    order_id = event.get("detail", {}).get("orderId", "unknown")
    dept = event.get("detail", {}).get("department", "unknown")
    return {"statusCode": 200, "body": f"Processed order {order_id} from {dept}"}

Step 3: Create a rule with event pattern

aws events put-rule \
  --name billing-orders-rule \
  --event-bus-name demo-orders-bus \
  --event-pattern '{
    "source": ["com.mycompany.orders"],
    "detail": {
      "department": ["billing"]
    }
  }' \
  --state ENABLED

Step 4: Add Lambda as target

aws events put-targets \
  --rule billing-orders-rule \
  --event-bus-name demo-orders-bus \
  --targets "Id"="lambda-target","Arn"="arn:aws:lambda:us-west-2:ACCOUNT:function:order-processor"

Step 5: Send a test event

aws events put-events --entries '[
  {
    "Source": "com.mycompany.orders",
    "DetailType": "Order Created",
    "Detail": "{\"orderId\":\"ORD-001\",\"department\":\"billing\",\"amount\":250}",
    "EventBusName": "demo-orders-bus"
  }
]'

Step 6: Check Lambda logs

aws logs tail /aws/lambda/order-processor --follow

Step 7: Send a non-matching event (should NOT trigger Lambda)

aws events put-events --entries '[
  {
    "Source": "com.mycompany.orders",
    "DetailType": "Order Created",
    "Detail": "{\"orderId\":\"ORD-002\",\"department\":\"shipping\",\"amount\":50}",
    "EventBusName": "demo-orders-bus"
  }
]'
# This event won't match the rule (department != "billing")

6. What's New (2024-2025 Updates)

• EventBridge Pipes - Point-to-point integrations with filtering, enrichment, and transformation (no custom code)
• EventBridge Schema Registry - Auto-discover event schemas, generate code bindings (TypeScript, Python, Java)
• EventBridge Global Endpoints - Active/active multi-region event routing with automatic failover
• SNS FIFO Topics - Strict message ordering + exactly-once delivery for event-driven workflows
• SNS Payload-Based Filtering - Filter on message body content (not just attributes) - reduces Lambda invocations
• EventBridge API Destinations - Route events to any HTTP endpoint (Slack, Datadog, custom APIs) with auth

7. Module Summary