Amazon SQS - Simple Queuing Service - FIFO vs Standard Queue - AWS Certification Cheat Sheet

Let’s get a quick overview of Amazon SQS from an AWS certification perspective. We will look at important certification questions regarding Amazon SQS.

You will learn

• What is Amazon SQS?
• Why do we need Amazon SQS?
• When do we use Amazon SQS?
• What is difference between FIFO vs Standard Queue?
• What are the steps involved in processing a message from Amazon SQS queue?
• How do you implement auto scaling with CloudWatch Alarms for SQS Queue?

Simple Queuing Service

Simple Queuing Service is a highly reliable, scalable, fully-managed message queuing service.

Here are some of the important features:

• High availability
• Unlimited scaling
  • Auto scale to process billions of messages per day
• Low cost (Pay for use)

Two Types of Simple Queuing Service Queues

There are Two Types of Simple Queuing Service Queues:

• Standard Queue
  • Unlimited throughput
  • BUT NO guarantee of ordering (Best-Effort Ordering)
  • and NO guarantee of exactly-once processing
    • Guarantees at-least-once delivery (some messages can be processed twice)
• FIFO (first-in-first-out) Queue
  • First-In-First-out Delivery
  • Exactly-Once Processing
  • BUT throughput is lower
    • Upto 300 messages per second (300 send, receive, or delete operations per second)
    • If you batch 10 messages per operation (maximum), up to 3,000 messages per second

Choose between Two Types of Simple Queuing Service Queues

• Standard SQS queue if throughput is important
• FIFO Queue if order of events is important

Sending and receiving a SQS Message - Best case scenario

Let’s see the steps involved in sending and receiving a message on the SQS queue:

• Step I: Producer places message on queue
  • Receives globally unique message ID ABCDEFGHIJ (used to track the message)
• Step II: Consumer polls for messages
  • Receives the message ABCDEFGHIJ along with a receipt handle XYZ
• Step III: Message remains in the queue while the consumer processes the message
  • Other consumers will not receive ABCDEFGHIJ even if they poll for messages
• Step IV: Consumer processes the message successfully
  • Calls delete message (using receipt handle XYZ)
  • Message is removed from the queue

Simple Queuing Service Lifecycle of a message

The picture below shows the service lifecycle of a message

When a message is sent to queue, it is redundantly distributed among SQS servers

SQS - Auto Scaling

You can also implement auto scaling for your SQS queue using CloudWatch based on number of messages in the queue.

Recommendations:

• Use target tracking scaling policy
• Use a SQS metric like ApproximateNumberOfMessages

SQS Queue - Important configuration

The table below shows some of the important SQS queue configuration:

Simple Queuing Service Security

Here are the important things to consider about security of the SQS queue:

• You can provide access to other AWS resources to access SQS using IAM roles (EC2 -> SQS)
• By default only the queue owner is allowed to use the queue
  • Configure SQS Queue Access Policy to provide access to other AWS accounts

SQS - Certification and Interview Questions

Let’s look a few scenarios regarding SQS.