Sending and receiving messages in AWS - Mini Project: Build & Apply

Sending and receiving messages with AWS SQS

📖 Scenario: You are building a simple messaging system using AWS Simple Queue Service (SQS). This system will send messages to a queue and then receive messages from it. This is useful for decoupling parts of an application so they can communicate reliably.

🎯 Goal: Create an AWS SQS queue, send a message to it, and then receive the message from the queue using AWS CLI commands.

📋 What You'll Learn

Create an SQS queue named MyTestQueue

Send a message with the exact body Hello from AWS SQS to MyTestQueue

Receive the message from MyTestQueue

Delete the message from the queue after receiving it

💡 Why This Matters

🌍 Real World

Messaging queues like AWS SQS are used in real applications to connect different parts of a system reliably, such as processing orders, notifications, or background tasks.

💼 Career

Understanding how to send and receive messages with SQS is a key skill for cloud engineers and developers working with distributed systems and serverless architectures.

1

Create an SQS queue

Use the AWS CLI command to create an SQS queue named MyTestQueue. Write the exact command starting with aws sqs create-queue --queue-name MyTestQueue.

AWS

# Your command here

Hint

Use the AWS CLI create-queue command with the --queue-name option.

2

Send a message to the queue

Send a message with the body Hello from AWS SQS to the queue MyTestQueue using the AWS CLI. Use the command starting with aws sqs send-message --queue-url and include the exact message body with --message-body "Hello from AWS SQS".

AWS

aws sqs create-queue --queue-name MyTestQueue
# Your command here

Hint

First, get the queue URL from the output of the create-queue command or AWS Console. Then use send-message with --message-body.

3

Receive the message from the queue

Use the AWS CLI command to receive a message from MyTestQueue. Write the command starting with aws sqs receive-message --queue-url and include the queue URL.

AWS

aws sqs create-queue --queue-name MyTestQueue
aws sqs send-message --queue-url https://sqs.us-east-1.amazonaws.com/123456789012/MyTestQueue --message-body "Hello from AWS SQS"
# Your command here

Hint

Use receive-message with the queue URL to get messages from the queue.

4

Delete the received message from the queue

After receiving the message, delete it from MyTestQueue using the AWS CLI. Use the command starting with aws sqs delete-message --queue-url and include the --receipt-handle parameter with the receipt handle from the received message.

AWS

aws sqs create-queue --queue-name MyTestQueue
aws sqs send-message --queue-url https://sqs.us-east-1.amazonaws.com/123456789012/MyTestQueue --message-body "Hello from AWS SQS"
aws sqs receive-message --queue-url https://sqs.us-east-1.amazonaws.com/123456789012/MyTestQueue
# Your command here

Hint

Use the receipt handle from the received message to delete it with delete-message.

Practice

1. What is the main purpose of sending messages in a cloud message queue service like AWS SQS?

easy

A. To put data into a queue so other parts can use it later

B. To delete data permanently from the system

C. To directly update a database record

D. To create a new virtual machine

Solution

1. Step 1: Understand message sending in queues

   Sending messages means placing data into a queue for later use by other parts of the system.

2. Step 2: Identify the purpose of sending messages

   The purpose is to store data temporarily so it can be processed asynchronously, not to delete or update directly.

3. Final Answer:

   To put data into a queue so other parts can use it later -> Option A

4. Quick Check:

   Sending messages = storing data in queue [OK]

Hint: Sending messages means putting data in a queue for later use [OK]

Common Mistakes:

• Confusing sending with deleting data
• Thinking sending updates databases directly
• Assuming sending creates compute resources

2. Which AWS service is primarily used for sending and receiving messages in a queue?

easy

A. Amazon EC2

B. Amazon SQS

C. Amazon RDS

D. Amazon S3

Solution

1. Step 1: Identify AWS services for messaging

   Amazon SQS (Simple Queue Service) is designed for sending and receiving messages in queues.

2. Step 2: Differentiate from other services

   EC2 is for servers, RDS for databases, and S3 for storage, not messaging queues.

3. Final Answer:

   Amazon SQS -> Option B

4. Quick Check:

   Message queue service = Amazon SQS [OK]

Hint: SQS is AWS's queue service for messages [OK]

Common Mistakes:

• Choosing EC2 which is for servers
• Confusing S3 storage with messaging
• Selecting RDS which is a database

3. Consider this AWS CLI command to receive a message from an SQS queue:
aws sqs receive-message --queue-url https://sqs.us-east-1.amazonaws.com/123456789012/MyQueue --max-number-of-messages 1
What will this command do?

medium

A. Create a new queue named MyQueue

B. Send one message to the queue

C. Delete one message from the queue

D. Receive up to one message from the queue

Solution

1. Step 1: Analyze the AWS CLI command

   The command uses receive-message with --max-number-of-messages 1, which means it tries to get up to one message from the queue.

2. Step 2: Understand the effect of the command

   It does not send, delete, or create queues. It only retrieves messages for processing.

3. Final Answer:

   Receive up to one message from the queue -> Option D

4. Quick Check:

   receive-message = get messages [OK]

Hint: receive-message gets messages, send-message puts them [OK]

Common Mistakes:

• Thinking receive-message sends messages
• Confusing receive with delete
• Assuming it creates queues

4. You wrote this code snippet to receive messages from an AWS SQS queue but it returns no messages:

response = sqs.receive_message(QueueUrl=queue_url, MaxNumberOfMessages=5)
messages = response['Messages']
for msg in messages:
    print(msg['Body'])

What is the likely cause of the error?

medium

A. The response has no 'Messages' key if the queue is empty

B. MaxNumberOfMessages must be 1, not 5

C. The queue URL is incorrect or empty

D. You must delete messages before receiving

Solution

1. Step 1: Understand SQS receive_message response

   If the queue is empty, the response does not include the 'Messages' key, causing a KeyError when accessing it.

2. Step 2: Identify the error cause

   Not checking if 'Messages' exists before looping causes failure when no messages are returned.

3. Final Answer:

   The response has no 'Messages' key if the queue is empty -> Option A

4. Quick Check:

   Empty queue means no 'Messages' key [OK]

Hint: Check if 'Messages' key exists before using it [OK]

Common Mistakes:

• Assuming 'Messages' always exists
• Setting MaxNumberOfMessages incorrectly
• Thinking messages must be deleted before receiving

5. You want to build a system that sends messages to an AWS SQS queue and ensures each message is processed exactly once by a receiver. Which combination of features should you use?

hard

A. Standard queue with short polling and no message deletion

B. Standard queue with long polling and message deletion after processing

C. FIFO queue with deduplication and message deletion after processing

D. FIFO queue without deduplication and no message deletion

Solution

1. Step 1: Understand message processing guarantees

   Standard queues can deliver messages more than once; FIFO queues preserve order and support exactly-once processing with deduplication.

2. Step 2: Ensure messages are deleted after processing

   Deleting messages after processing prevents reprocessing the same message.

3. Step 3: Combine features for exactly-once processing

   Use FIFO queue with deduplication and delete messages after processing to guarantee exactly-once delivery.

4. Final Answer:

   FIFO queue with deduplication and message deletion after processing -> Option C

5. Quick Check:

   Exactly-once = FIFO + deduplication + delete [OK]

Hint: Use FIFO queue with deduplication and delete messages after processing [OK]

Common Mistakes:

• Using standard queue for exactly-once needs
• Not deleting messages after processing
• Ignoring deduplication feature