SNS and SQS integration pattern (fan-out) in AWS - Mini Project: Build & Apply

SNS and SQS Integration Pattern (Fan-Out)

📖 Scenario: You are building a notification system where one message sent to a topic needs to be delivered to multiple queues for different processing tasks.This is a common pattern called fan-out, where a single message is copied and sent to multiple destinations.

🎯 Goal: Create an AWS CloudFormation template that sets up an SNS topic and two SQS queues. Then subscribe both queues to the SNS topic to enable fan-out messaging.

📋 What You'll Learn

Create an SNS topic named MyTopic

Create two SQS queues named QueueA and QueueB

Subscribe both QueueA and QueueB to MyTopic

Ensure the subscriptions use the correct protocol and reference the queue ARNs

💡 Why This Matters

🌍 Real World

Fan-out messaging is used in systems where one event triggers multiple independent processing tasks, such as sending notifications, updating databases, and logging.

💼 Career

Understanding SNS and SQS integration is essential for cloud architects and developers building scalable, decoupled event-driven systems on AWS.

1

Create the SNS topic

Create an SNS topic resource named MyTopic in the CloudFormation template.

AWS

# Define the SNS topic resource
# Your code here

Hint

Use AWS::SNS::Topic as the resource type and set TopicName to MyTopic.

2

Create two SQS queues

Add two SQS queue resources named QueueA and QueueB to the CloudFormation template.

AWS

Resources:
  MyTopic:
    Type: AWS::SNS::Topic
    Properties:
      TopicName: MyTopic
# Add SQS queue resources named QueueA and QueueB below
# Your code here

Hint

Use AWS::SQS::Queue as the resource type and set QueueName to QueueA and QueueB respectively.

3

Subscribe QueueA to the SNS topic

Add a subscription resource named SubscriptionA that subscribes QueueA to MyTopic using the sqs protocol and the ARN of QueueA.

AWS

Resources:
  MyTopic:
    Type: AWS::SNS::Topic
    Properties:
      TopicName: MyTopic
  QueueA:
    Type: AWS::SQS::Queue
    Properties:
      QueueName: QueueA
  QueueB:
    Type: AWS::SQS::Queue
    Properties:
      QueueName: QueueB
# Add a subscription resource named SubscriptionA to subscribe QueueA to MyTopic
# Your code here

Hint

Use AWS::SNS::Subscription and set TopicArn to !Ref MyTopic, Protocol to sqs, and Endpoint to !GetAtt QueueA.Arn.

4

Subscribe QueueB to the SNS topic

Add a subscription resource named SubscriptionB that subscribes QueueB to MyTopic using the sqs protocol and the ARN of QueueB.

AWS

Resources:
  MyTopic:
    Type: AWS::SNS::Topic
    Properties:
      TopicName: MyTopic
  QueueA:
    Type: AWS::SQS::Queue
    Properties:
      QueueName: QueueA
  QueueB:
    Type: AWS::SQS::Queue
    Properties:
      QueueName: QueueB
  SubscriptionA:
    Type: AWS::SNS::Subscription
    Properties:
      TopicArn: !Ref MyTopic
      Protocol: sqs
      Endpoint: !GetAtt QueueA.Arn
# Add a subscription resource named SubscriptionB to subscribe QueueB to MyTopic
# Your code here

Hint

Use AWS::SNS::Subscription and set TopicArn to !Ref MyTopic, Protocol to sqs, and Endpoint to !GetAtt QueueB.Arn.

Practice

1. What is the main purpose of using SNS with multiple SQS queues in a fan-out pattern?

easy

A. To send the same message to multiple queues for parallel processing

B. To store messages permanently in one queue

C. To send messages only to one queue at a time

D. To delete messages immediately after sending

Solution

1. Step 1: Understand SNS role in fan-out

   SNS publishes messages to multiple subscribers simultaneously.

2. Step 2: Understand SQS role in fan-out

   Each SQS queue receives and holds messages independently for processing.

3. Final Answer:

   To send the same message to multiple queues for parallel processing -> Option A

4. Quick Check:

   SNS fan-out = multiple queues get same message [OK]

Hint: SNS fan-out means one message to many queues [OK]

Common Mistakes:

• Thinking SNS sends to only one queue
• Confusing message storage with deletion
• Assuming messages are deleted immediately

2. Which of the following is the correct way to subscribe an SQS queue to an SNS topic using AWS CLI?

easy

A. aws sns subscribe --topic-arn --protocol sqs --notification-endpoint

B. aws sqs subscribe --topic-arn --queue-url

C. aws sns create-subscription --topic --queue

D. aws sns add-queue --topic-arn --queue-arn

Solution

1. Step 1: Identify correct AWS CLI command

   The AWS CLI command to subscribe is 'aws sns subscribe'.

2. Step 2: Check parameters for SQS subscription

   Use '--protocol sqs' and '--notification-endpoint' with the queue ARN.

3. Final Answer:

   aws sns subscribe --topic-arn <topic-arn> --protocol sqs --notification-endpoint <queue-arn> -> Option A

4. Quick Check:

   Subscribe SQS to SNS uses 'aws sns subscribe' with protocol sqs [OK]

Hint: Subscribe SQS with 'aws sns subscribe' and protocol sqs [OK]

Common Mistakes:

• Using 'aws sqs subscribe' which does not exist
• Confusing queue URL with queue ARN
• Using wrong command like 'aws sns add-queue'

3. Given an SNS topic with two subscribed SQS queues, if a message is published to SNS, what will be the state of the message in the queues?

medium

A. The message is deleted from SNS and not delivered to any queue.

B. The message appears in only one queue randomly.

C. The message appears in both queues independently, waiting to be processed.

D. The message is duplicated in one queue only.

Solution

1. Step 1: Understand SNS fan-out delivery

   SNS sends a copy of the message to each subscribed queue.

2. Step 2: Understand SQS message handling

   Each queue holds its own copy until processed or deleted.

3. Final Answer:

   The message appears in both queues independently, waiting to be processed. -> Option C

4. Quick Check:

   Fan-out means each queue gets its own message copy [OK]

Hint: SNS fan-out sends message copy to each queue [OK]

Common Mistakes:

• Thinking message goes to only one queue
• Assuming message is deleted immediately
• Believing message duplicates in one queue only

4. You configured an SNS topic with two SQS queues subscribed, but only one queue receives messages. What is the most likely cause?

medium

A. SNS only sends messages to one queue by design

B. The second queue's subscription is not confirmed

C. The message size exceeds SNS limits

D. The first queue deleted the message too fast

Solution

1. Step 1: Check subscription confirmation

   SQS subscriptions to SNS require confirmation to activate delivery.

2. Step 2: Understand SNS delivery behavior

   Without confirmation, SNS does not send messages to that queue.

3. Final Answer:

   The second queue's subscription is not confirmed -> Option B

4. Quick Check:

   Unconfirmed subscription blocks message delivery [OK]

Hint: Confirm all subscriptions to receive messages [OK]

Common Mistakes:

• Assuming SNS sends to only one queue
• Blaming message size without checking subscription
• Thinking message deletion affects delivery

5. You want to build a system where an SNS topic sends messages to three SQS queues. One queue processes orders, another sends notifications, and the third logs events. How should you configure the system to ensure reliable processing and no message loss?

hard

A. Subscribe only the order queue to SNS and forward messages to others manually

B. Send messages directly to each SQS queue without SNS

C. Use one SQS queue for all processing and filter messages inside the consumer

D. Subscribe all three SQS queues to the SNS topic, enable dead-letter queues for each, and set appropriate message retention

Solution

1. Step 1: Use SNS fan-out to send messages to all queues

   Subscribing all three SQS queues to the SNS topic ensures each gets the message.

2. Step 2: Enable dead-letter queues and set retention

   Dead-letter queues catch failed messages; retention ensures messages stay until processed.

3. Final Answer:

   Subscribe all three SQS queues to the SNS topic, enable dead-letter queues for each, and set appropriate message retention -> Option D

4. Quick Check:

   Fan-out + DLQ + retention = reliable, no message loss [OK]

Hint: Use fan-out with DLQ and retention for reliability [OK]

Common Mistakes:

• Skipping dead-letter queues causing message loss
• Using one queue for all processing causing bottlenecks
• Not subscribing all queues to SNS topic