03. Amazon SNS (Simple Notification Service)
Amazon SNS (Simple Notification Service) enables asynchronous, one-to-many (Pub/Sub) messaging between distributed systems and microservices. It allows a single message to be broadcast to multiple subscribers instantly ideal for notifications and fan-out messaging.
When one service needs to send the same message to multiple receivers, direct integrations can get messy.
Instead of connecting to each service individually, we use SNS Topics.
⚙️ How It Works
| Component | Role |
|---|---|
| Publisher (Producer) | Sends a message to an SNS Topic. |
| Topic | Acts as a central hub for distributing messages. |
| Subscribers (Consumers) | Receive messages from the topic, all subscribers get a copy. |
✅ One publisher → many subscribers.
✅ Each subscriber gets all messages.
✅ No need for multiple direct integrations.
🌐 Example Use Case
Scenario: An e-commerce platform where the Buying Service needs to notify multiple systems.
| Destination | Description |
|---|---|
| Email Service | Sends order confirmation email. |
| Fraud Service | Checks order legitimacy. |
| Shipping Service | Starts shipment preparation. |
| SQS Queue | Sends order info for further processing. |
✅ All notifications sent simultaneously from a single publish action.
⚡ Scalability & Limits
| Feature | Value |
|---|---|
| Subscribers per Topic | Up to 12 million |
| Topics per Account | Soft limit of 100,000 |
| Destinations Supported | SQS, Lambda, Firehose, Email, SMS, Mobile Push, HTTP/S Endpoints |
| Latency | Near real-time (milliseconds) |
| Delivery Retries | Automatic for supported protocols |
🧠 Exam Tips
| Keyword | Think Of |
|---|---|
| Notification | SNS |
| Pub/Sub model | SNS |
| Fan-out pattern | SNS |
| Broadcast to multiple systems | SNS |
| One-to-many communication | SNS |
🔁 SNS vs SQS Comparison
| Feature | SQS (Queue) | SNS (Topic) |
|---|---|---|
| Model | Point-to-Point | Publish/Subscribe |
| Message Delivery | Delivered to one consumer instance | Delivered to all subscribers |
| Persistence | Messages stored until processed | Messages pushed immediately |
| Use Case | Decouple producer and consumer | Broadcast events to multiple receivers |
| Example | Order processing queue | Send “OrderPlaced” to Email, SMS, Billing services |
🧩 Fan-Out Pattern
SNS and SQS are often used together — SNS sends a message to multiple SQS queues.
✅ Reliable and scalable broadcast
✅ Each service processes messages independently
✅ Perfect for decoupled microservice architectures
🧠 Key Takeaway
Amazon SNS allows a single message to be instantly broadcast to multiple subscribers
Ideal for notifications, alerts, and fan-out integration patterns.
Think "Publish/Subscribe" whenever you need one-to-many communication.
SNS Hands On
- Create Topic (Email is subscribe here)
- Publishing message works
🔹 SQS → Pull model (polling required) 🔹 SNS → Push model (automatic delivery)