SNS and SQS integration pattern (fan-out) in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of the SNS and SQS fan-out pattern?

It allows a single message published to an SNS topic to be delivered to multiple SQS queues, enabling parallel processing by different consumers.

beginner

How does SNS deliver messages to SQS queues in the fan-out pattern?

SNS pushes the message to all subscribed SQS queues immediately after a message is published to the SNS topic.

intermediate

Why use SQS queues with SNS instead of having multiple subscribers directly on SNS?

SQS queues provide message durability, decoupling, and allow consumers to process messages at their own pace, improving reliability and scalability.

intermediate

What happens if one SQS queue subscriber is slow or down in the fan-out pattern?

The other queues still receive and process messages independently; the slow or down queue will accumulate messages until it recovers.

advanced

What is a best practice when configuring SNS and SQS fan-out integration?

Ensure each SQS queue has proper permissions to allow SNS to send messages, and configure dead-letter queues for handling failed message processing.

What AWS service acts as the message publisher in the fan-out pattern?

A DynamoDB

B SQS

C SNS

D Lambda

SNS is the service that publishes messages to multiple subscribers, including SQS queues.

In the fan-out pattern, how many SQS queues can an SNS topic send messages to?

A None

B Exactly two

C Only one

D Multiple, unlimited

SNS can deliver messages to multiple subscribed SQS queues simultaneously.

What feature of SQS helps handle messages if a consumer fails to process them?

A Auto-scaling

B Dead-letter queue

C Encryption

D Caching

Dead-letter queues store messages that could not be processed successfully for later inspection or reprocessing.

Which of the following is NOT a benefit of using the SNS and SQS fan-out pattern?

A Guaranteed message order across all queues

B Parallel processing of messages

C Decoupling of message producers and consumers

D Improved fault tolerance

SNS and SQS fan-out does not guarantee message order across multiple queues.

What must you configure to allow SNS to send messages to an SQS queue?

A SQS queue policy to allow SNS publish

B SNS topic policy to allow SQS subscribe

C IAM user permissions only

D No configuration needed

The SQS queue must have a policy that permits the SNS topic to send messages to it.

Explain how the SNS and SQS fan-out pattern works and why it is useful.

Think about one message reaching many receivers independently.

Describe best practices when setting up SNS and SQS fan-out integration.

Focus on security, reliability, and monitoring.

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