AWS Solutions Architecture for Fan-Out Pattern Delivery to Multiple SQS | Deep Dive.

AWS Solutions Architecture for Fan-Out Pattern Delivery to Multiple SQS - Deep Dive.

 Scope:

• The concept of Fan-Out Pattern,
• AWS Services in Fan-Out Pattern,
• Architecture Diagram,
• Step-by-Step Implementation,

• Step 1: Create an SNS Topic,

• Step 2: Create Multiple SQS Queues,

• Step 3: Subscribe SQS Queues to SNS Topic,

• Step 4: (Optional) Lambda Triggers,

• Key Considerations,
• Advanced Patterns,
• Benefits of This Architecture.

1. The concept of Fan-Out Pattern

• The Fan-Out pattern is used when a single event or single message needs to be processed by multiple independent consumers.
• Publisher: The component that generates the event (e.g., a Lambda function or an application).
• Broker: A messaging service (like SNS) that distributes the event to multiple subscribers.
• Subscribers: The endpoints that consume the event (e.g., multiple SQS queues, Lambda functions, or HTTP endpoints).

Use-case Samples:

•  Order placed → Notify inventory system, shipping system, and analytics system.
•  User signup → Trigger welcome email, log analytics, and create CRM entry.

2. AWS Services in Fan-Out Pattern

SNS (Simple Notification Service)

• Acts as a pub/sub messaging broker.
• Supports multiple protocols: SQS, Lambda, HTTP/S, Email, SMS.
• Can fan out a single message to many subscribers simultaneously.

SQS (Simple Queue Service)

• Durable queue for decoupling services.
• Each subscriber can process messages independently and reliably.
• Supports FIFO queues for ordering or standard queues for high throughput.

Lambda (Optional)

• Can act as publisher or subscriber.
• Processes messages from SQS queues asynchronously

3. Architecture Diagram

Explanation:

1.  Publisher pushes message to SNS topic.
2.  SNS fans out the message to multiple SQS queues.
3.  Each SQS queue triggers its own Lambda processor, decoupling workloads.

4. Step-by-Step Implementation

Step 1: Create an SNS Topic

# yaml

aws sns create-topic --name fanout-topic

Step 2: Create Multiple SQS Queues

# yaml

aws sqs create-queue --queue-name queue1

aws sqs create-queue --queue-name queue2

aws sqs create-queue --queue-name queue3

Step 3: Subscribe SQS Queues to SNS Topic

# yaml

aws sns subscribe --topic-arn <SNS_TOPIC_ARN> \ 

--protocol sqs --notification-endpoint <SQS_QUEUE_ARN>

Step 4: (Optional) Lambda Triggers

•    Each SQS queue can trigger a Lambda function to process messages asynchronously.

Lambda Example (Python):

# python

import json

def lambda_handler(event, context):

    for record in event['Records']:

        body = json.loads(record['body'])

        print("Processing:", body)

5. Key Considerations

Message Delivery

• SNS delivers messages at least once.
• SQS ensures durable storage.

Decoupling

• Each SQS queue processes messages independently, preventing bottlenecks.
• Failures in one consumer do not affect others.

Dead Letter Queue (DLQ)

•  For failed messages in SQS or Lambda, configure a DLQ to capture them for later inspection.

Scaling

•  SNS scales automatically.
•  SQS queues can scale independently.
•  Lambda concurrency can be tuned per queue.

Ordering

• Standard SQS queues: at least once, no ordering guarantee.
• FIFO SQS queues: exactly once, preserves order.
• SNS + FIFO SQS = strict ordering support.

6. Advanced Patterns

Message Filtering

• SNS supports subscription filters.
• Allows selective delivery to queues based on message attributes:

# json

{

  "eventType": ["order_placed", "order_shipped"]

}

Cross-Account Fan-Out

•  SNS can fan out messages to SQS queues in different AWS accounts, enabling multi-tenant architectures.

Monitoring

• Use CloudWatch metrics for:
•    SNS: NumberOfMessagesPublished
•    SQS: ApproximateNumberOfMessagesVisible
•    Lambda: Invocations, Errors, Throttles

7. Benefits of This Architecture

• Loose coupling: Each service operates independently.
• Scalable: SNS and SQS scale horizontally.
• Reliable: Durable queues + DLQs handle failures gracefully.
• Flexible: Easy to add new subscribers without affecting others.