SNS and SQS integration pattern (fan-out) in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

SNS Fan-out Pattern: Message Delivery Count

You have an SNS topic connected to two SQS queues using the fan-out pattern. When a single message is published to the SNS topic, how many messages will each SQS queue receive?

A Each SQS queue receives multiple copies of the message.

B Only one SQS queue receives the message; the other receives none.

C Each SQS queue receives exactly one copy of the message.

D No SQS queue receives the message automatically.

💡 Hint

Think about how SNS distributes messages to multiple subscribers.

In the fan-out pattern, SNS sends a copy of each message to every subscribed SQS queue. So each queue gets exactly one copy.

❓ Architecture

intermediate

Designing for Message Durability in SNS to SQS Fan-out

You want to ensure that messages published to an SNS topic are not lost even if one of the SQS queues is temporarily unavailable. Which configuration best supports this requirement?

A Set SQS queues to non-durable mode to improve performance.

B Use SNS only without SQS queues to simplify the architecture.

C Configure SQS queues without DLQs and rely on SNS to store messages.

D Enable SNS message retries and configure SQS queues with dead-letter queues (DLQs).

💡 Hint

Consider how to handle message failures and retries in distributed systems.

Enabling SNS retries and configuring DLQs on SQS queues ensures messages are retried and not lost if queues are unavailable.

❓ security

advanced

Securing SNS to SQS Fan-out Communication

To restrict which SNS topics can send messages to your SQS queues in a fan-out pattern, what is the best practice?

A Attach an SQS queue policy that allows only specific SNS topic ARNs to send messages.

B Use IAM roles on the SNS topic to restrict sending messages.

C Enable encryption on the SNS topic to block unauthorized messages.

D Configure SNS topic policies to deny all SQS queues.

💡 Hint

Think about how SQS controls who can send messages to it.

SQS queue policies specify which SNS topics are allowed to send messages, controlling access securely.

❓ Configuration

advanced

Configuring SQS Queue to Receive Messages from SNS Topic

Which AWS CLI command correctly subscribes an SQS queue to an SNS topic to implement fan-out?

A aws sns add-subscription --topic arn:aws:sns:region:123456789012:MyTopic --protocol sqs --endpoint arn:aws:sqs:region:123456789012:MyQueue

B aws sns create-subscription --topic-arn arn:aws:sns:region:123456789012:MyTopic --protocol sqs --endpoint arn:aws:sqs:region:123456789012:MyQueue

C aws sns subscribe --topic-arn arn:aws:sns:region:123456789012:MyTopic --protocol sqs --notification-endpoint arn:aws:sqs:region:123456789012:MyQueue

D aws sqs subscribe --queue-url https://sqs.region.amazonaws.com/123456789012/MyQueue --topic-arn arn:aws:sns:region:123456789012:MyTopic

💡 Hint

Check the exact AWS CLI command syntax for SNS subscriptions.

The correct command is aws sns subscribe with the topic ARN, protocol, and endpoint parameters.

✅ Best Practice

expert

Optimizing Throughput in SNS to SQS Fan-out Architecture

You have an SNS topic fan-out to multiple SQS queues. You notice message processing is slow due to high message volume. Which approach best improves throughput without losing messages?

A Enable batching on SQS consumers and increase the number of consumers per queue.

B Reduce the number of SQS queues subscribed to the SNS topic.

C Disable message deduplication on SQS queues to speed up processing.

D Increase the SNS message delivery retry interval to reduce load.

💡 Hint

Think about how to process messages faster in queues.

Batching messages and scaling consumers allows faster processing without message loss.

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