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

A deep dive into a Fan-Out architecture using AWS Lambda, SNS, and SQS.

 Scope:

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

•         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.