Amazon SNS

Amazon Simple Notification Service (SNS) is a fully managed pub/sub messaging service that enables you to decouple microservices, distributed systems, and serverless applications.

Key Concepts

• Topics: Communication channels for publishing messages
• Publishers: Services that send messages to topics
• Subscribers: Endpoints that receive messages from topics
• Messages: Up to 256 KB of data in various formats

Subscription Types

Endpoint	Use Case
Lambda	Serverless processing
SQS	Queue-based processing
HTTP/HTTPS	Webhook integrations
Email	Notifications to people
SMS	Text message alerts
Mobile push	iOS, Android notifications

Common Patterns

Fan-out

One message to multiple consumers:

Publisher → SNS Topic → [SQS Queue 1, SQS Queue 2, Lambda]

Alerting

CloudWatch Alarm → SNS → [Email, SMS, PagerDuty webhook]

Event Broadcasting

Application → SNS → Multiple microservices

Example: Publishing a Message

const sns = new AWS.SNS();
await sns.publish({
  TopicArn: 'arn:aws:sns:us-east-1:123456789:my-topic',
  Message: JSON.stringify({ event: 'order_placed', orderId: '12345' }),
  MessageAttributes: {
    eventType: { DataType: 'String', StringValue: 'order_placed' }
  }
}).promise();

What We Like

• Simplicity: Easy to set up and use
• Fan-out: One publish, many subscribers
• Durability: Messages are stored across multiple AZs
• Filtering: Route messages to subscribers based on attributes

What We Don't Like

• No replay: Messages can't be re-read once consumed (unlike EventBridge)
• Limited retention: Failed deliveries have limited retry windows
• Ordering: Standard topics don't guarantee order (FIFO topics do, with limitations)

SNS vs SQS vs EventBridge

Feature	SNS	SQS	EventBridge
Pattern	Pub/Sub	Queue	Event bus
Consumers	Many	One (per message)	Many
Replay	No	No	Yes (archive)
Filtering	Basic	No	Advanced