Amazon Simple Notification Service(SNS).

Sunday, July 20, 2025

Amazon Simple Notification Service(SNS).

Amazon Simple Notification Service(SNS)

Amazon SNS is a fully managed pub/sub (publish/subscribe) messaging service used to send messages from producers (publishers) to multiple consumers (subscribers) asynchronously.

Key Use Cases

Use Case	Description
Application decoupling	Producers publish messages; subscribers process independently.
Fan-out pattern	One message sent to many endpoints (e.g., Lambda, SQS, HTTP).
Mobile push notifications	Sends notifications to iOS, Android, Fire OS devices.
Email/SMS alerts	Sends alerts to users or admins.
Workflow triggers	Event-based architecture (e.g., image upload → start processing pipeline).

Core Concepts

Topic: A logical access point where publishers send messages.
Publisher: The sender (e.g., application, Lambda, script).
Subscriber: Endpoints that receive messages from a topic.
Subscription: A configuration that connects a topic to a subscriber.

Supported Protocols for Subscribers

Protocol	Example
SQS	Queue receives message. Good for decoupling or buffering.
Lambda	Message triggers Lambda function.
HTTP/S	POSTs message to a webhook or REST endpoint.
Email	Sends text message to an email address.
SMS	Sends text message to a mobile phone.
Application	Sends push notifications to mobile devices.

How SNS Works (Fan-out Example)

# Plaintext

[Publisher]

[SNS Topic] twtech-SNS-Topic

| |

[SQS Queue] [Lambda Function]

One message sent to the SNS topic.
All subscribers receive a copy of the message simultaneously.

Security & Permissions

IAM policies: Control who can publish or subscribe.
Topic access policies: Restrict which AWS accounts/services can interact.
Encryption: Support for server-side encryption using AWS KMS.
Message filtering: Subscribers can filter messages by attributes (e.g., only receive certain event types).

Features at a Glance

Feature	Description
Message fan-out	Send a message to many endpoints.
Message filtering	Subscribers get only messages they care about.
Durability	High availability and redundancy.
Push-based	Instantly delivers messages — no polling.
Global reach	SMS/email/mobile push globally.

SNS vs. SQS

Feature	SNS	SQS
Model	Pub/Sub (Push)	Message Queue (Pull)
Delivery	Pushes to multiple subscribers	Consumers poll for messages
Use Case	Notifications, fan-out, alerts	Decoupling, buffering, retries
Ordering	No ordering guarantees	FIFO queues available
Retry Logic	Retry per subscriber protocol	Built-in redrive policy

Example: Using SNS + SQS Fan-Out

Create an SNS topic.
Create two SQS queues.
Subscribe both SQS queues to the SNS topic.
Publish a message to the topic → both queues receive a copy.

twtech insights:

What "Asynchronously" Means in AWS Context.

"Asynchronously" means that tasks or communication between services happen independently and non-blocking — the sender doesn’t wait for the receiver to finish processing.

Example in AWS: SNS + SQS = Asynchronous Flow

Let’s say you have a web application that processes image uploads.

Without Asynchronous Messaging (synchronous):

# plaintext

[Web App]

    | (publishes)

  [SNS Topic]

    | (forwards message)

  [SQS Queue] ---> [Worker Processes] ---> [Database]

· The web app publishes a message to SNS.

· SNS asynchronously delivers the message to an SQS queue.

· Worker processes pull from the queue and process the image independently.

· The web app can immediately return a response like “Upload received.”

Benefits of Asynchronous Design

Benefit	Why It Matters
Low latency	Sender doesn't wait — better user experience.
Resilience	Systems continue operating even if downstream is slow/down.
Scalability	Easier to scale consumers based on message volume.
Decoupling	Components evolve independently — no direct dependencies.
Retry logic	Messages can be retried without re-sending from sender.

Asynchronous Tools in AWS

Service	Role in Asynchronous Communication
Amazon SQS	Buffer messages for consumers to process later.
Amazon SNS	Publish messages to many consumers instantly.
AWS Lambda	Responds to events without needing direct integration.
EventBridge	Event bus for routing events across AWS services.

How twtech may send a single massages to may recievers.

NB:

twtech may have up to 12,500,000 subscriptions per topic.

twtech may have up to 100,000 topics.

SNS integrates with a lot of AWS services. The following services can send data directly to SNS for notifications.

· CloudWatch Alarms,

· S3 Bucket (Events),

· Auto Scaling Group (Notifications),

· CloudFormation (State Changes),

· AWS Budgets,

· Lambda,

· AWS DMS (New Replic),

· DynamoDB RDS Events.

Project: Hands-on

How twtech creates and use SNS for Messagig.

Search for the aws service: SNS (Simple Notification Service)

Add a topic name and create an SNS topic: twtech-SNS-Topic

Select Type: Standard

Topic type cannot be modified after topic is created.

Encryption - optional

Amazon SNS provides in-transit encryption by default. Enabling server-side encryption adds at-rest encryption to your topic.

Access policy - optional

This policy defines who can access your topic. By default, only the topic owner can publish or subscribe to the topic.

Data protection policy - optional

This policy defines which sensitive data to monitor and to prevent from being exchanged via your topic.

Delivery policy (HTTP/S) - optional

The policy defines how Amazon SNS retries failed deliveries to HTTP/S endpoints. To modify the default settings, expand this section.

Delivery status logging - optional

These settings configure the logging of message delivery status to CloudWatch Logs.

Tags - optional

A tag is a metadata label that you can assign to an Amazon SNS topic. Each tag consists of a key and an optional value. You can use tags to search and filter your topics and track your costs.