Amazon Sns

Decoupling Applications with Amazon SNS

Publish/Subscribe Messaging Model

Core Concepts

Publish/Subscribe (pub/sub) messaging enables asynchronous communication when sending applications broadcast messages to multiple receiving applications with little or no knowledge about recipients.

Key Components:

• Publisher: Sending application that publishes messages to topics
• Subscriber: Receiving applications that subscribe to topics to receive messages
• Topic: Interim destination that broadcasts messages to subscribers
• Push Mechanism: Eliminates need for periodic polling, messages pushed immediately

Messaging Flow

1. Recipients subscribe to topics of interest
2. Publisher publishes message to topic
3. Topic automatically pushes messages to all subscribers asynchronously

Unlike message queues that store messages until retrieved, topics transfer messages with minimal queueing and push immediately to all subscribers.

Amazon Simple Notification Service (Amazon SNS)

Service Overview

Amazon SNS is a fully managed pub/sub messaging service that:

• Sets up, operates, and sends notifications from the cloud
• Follows push mechanism for notification delivery
• Meets demands of largest applications with unlimited message publishing
• Provides no maintenance overhead with pay-as-you-go pricing

Core Features

• Topic Creation: Unique names identify SNS endpoints for publishers and subscribers
• Policy Control: Restricts who can publish or subscribe to topics
• Universal Delivery: All subscribers receive same messages from subscribed topics
• Secure Communication: TLS support for publishers and subscribers
• Durable Storage: Multiple copies stored across Availability Zones during processing
• No Persistence: Messages deleted after publishing to subscribers

Types of Subscribers

Amazon SNS supports multiple destination types for message delivery:

Email Destination

Messages sent to registered email addresses in text or JSON format

Mobile SMS

Short Message Service (SMS) text messages to registered phone numbers

Mobile Push

Native push notifications to mobile device endpoints

HTTP/HTTPS Endpoints

Messages sent to URL addresses via HTTP POST requests

Advanced Integration Subscribers:

• AWS Lambda Function: Invoke custom business logic
• SQS Queue: Store messages for later processing by receiver applications
• Amazon Kinesis Data Firehose: Deliver to storage and analytics endpoints

Use Cases

Primary Applications

• Application and System Alerts: Immediate notification for events like Auto Scaling group changes
• Push Email and Text Messaging: Targeted news headlines to subscribers via email or SMS
• Mobile Push Notifications: App update notifications with download links

Fanout Scenario Example

Image Processing Architecture: Mobile client uploads image for conversion into three different sizes

Flow Process:

1. Mobile app uploads image to S3 bucket
2. S3 event notification publishes message to SNS topic with object URL
3. Topic fans out simultaneously to three SQS queues:
   • Generate thumbnail queue
   • Size for mobile queue
   • Size for web queue
4. Each queue monitored by separate Auto Scaling applications
5. Applications perform independent resizing and store results in converted images bucket

This architecture enables parallel asynchronous processing with automatic scaling based on workload.

Amazon SNS Considerations

Message Publishing Characteristics

• Single Message: Each notification contains one published message
• No Recall: Successfully delivered messages cannot be recalled
• Topic Types:
  • Standard: Best-effort ordering, potential out-of-order delivery
  • FIFO: Strict message ordering preservation

Delivery Policies

Retry Behavior Control: Amazon SNS defines delivery policies for each protocol

• Controls retry patterns when subscribed endpoints become unavailable
• HTTP/HTTPS Exception: Only endpoints with customizable delivery policies
• Dead Letter Queue: Attaches to subscription when delivery policy exhausted
• Message Discard: Without DLQ, messages discarded after policy exhaustion

Amazon SNS vs Amazon SQS Comparison

Amazon SNS

• Messaging Model: Publisher-Subscriber
• Distribution: One to many
• Delivery: Push (passive)
• Persistence: No message persistence

Amazon SQS

• Messaging Model: Producer-Consumer
• Distribution: One to one
• Delivery: Pull (active)
• Persistence: Messages persist until deleted

Key Differences

• SNS Publishers don’t necessarily know subscribers; SQS Producers know message consumers
• SNS requires subscribers available at publication time; SQS consumers can be offline when messages sent
• SNS messages deleted after publishing; SQS messages persist until consumer deletion or retention limit

Integration with Amazon SQS

Combined Architecture Benefits: Using SNS with SQS provides highly available message routing for effective distribution to decoupled application functions.

Fanout Pattern: SNS topic replicates and pushes messages to multiple SQS queues, HTTP endpoints, or email addresses for parallel processing.

This combination leverages the strengths of both services - SNS for broadcast distribution and SQS for reliable message queuing and processing.

Pub/Sub Service

Note

Event-Driven Architecture Amazon SNS enables AWS services to publish messages to topics, invoking event-driven computing and automated workflows across your infrastructure.