SNS (Event broadcaster)

SNS (Simple Notification Service) is an Event broadcaster that fans out messages to multiple subscribers.

SNS is a fully managed pub/sub messaging service where publishers send messages to topics and these messages are automatically delivered to all subscribed endpoints/consumers.

Key Features:

• Message size:

  • Standard: Up to 256 KB of text in any format

  • Extended: Up to 2 GB using Amazon SNS Extended Client Library (stores payload in S3)

• Encryption:

  • In-transit encryption by default

  • At-rest encryption using KMS (optional)

• Access Control:

  • IAM policies

  • SNS Access policies (define who can publish/subscribe)

Supported Subscribers:

• Application integration:

  • Amazon SQS

  • AWS Lambda

  • Amazon Kinesis Data Firehose

• Messaging:

  • HTTP/HTTPS endpoints

  • Email

  • SMS

  • Mobile push notifications

  • Platform application endpoints

Message Filtering:

• Subscription filter policies allow filtering messages before delivery

• Reduces unnecessary message processing

Message Reliability:

• Dead Letter Queues (DLQ) support for failed message delivery

• Custom retry policies supported for HTTP/HTTPS endpoints

• Message durability through multiple Availability Zone replication

Messaging Types:

• Standard Topics:

  • Best-effort ordering

  • At-least-once delivery

• FIFO Topics:

  • Strict message ordering

  • Exactly-once message delivery

  • Must have SQS FIFO queues as subscribers

SNS Fanout Pattern:

• Pushes messages to multiple subscribing endpoints simultaneously

• Enables parallel, asynchronous processing

• Provides complete decoupling between publishers and subscribers

• Common use cases:

  • Application alerts

  • Monitoring systems

  • Workflow processing

  • Cross-account/cross-region message delivery

SNS Topic Subscribers Models:

SNS topic subscribers can be registered in two ways:

1. Subscription Registration (Push Model):

• The topic owner creates the subscription

• Done through AWS Console, AWS CLI, or AWS SDKs

• You specify the endpoint (like an SQS queue, Lambda function, HTTP/S endpoint, email, etc.)

• For HTTP/S endpoints, SNS sends a subscription confirmation message

• The endpoint must confirm the subscription by sending back the token

1. Subscription Request (Pull Model):

• The subscriber initiates the subscription request

• Used mainly for cross-account scenarios

• Requires explicit approval from the topic owner

• Topic owner must have a subscription policy allowing the request

Supported endpoint types include:

• Amazon SQS queues

• AWS Lambda functions

• HTTP/HTTPS endpoints

• Email addresses

• Mobile push notifications

• SMS messages

• Amazon Kinesis Data Firehose

For protocols requiring authentication (like HTTPS), the endpoint must actively confirm the subscription by responding to SNS's confirmation message before messages can be received

Best Practices:

• Use filter policies to reduce unnecessary message delivery

• Implement DLQ for handling failed deliveries

• Monitor delivery metrics using CloudWatch

• Use FIFO topics when message ordering is critical