CMSC389L

SQS

Message Queues

• Message Queue: A shared queue that enables asynchronous communication of messages between processes.

Why decouple components?

• Strongly coupled components form complex systems
  • Hard to maintain/expand/refactor
• Instead:
  • Encapsulate the inner workings of each component
  • Expose a limited API

Decoupling: Microservices

Why use message queues?

• What happens if the Service B dies?
• What happens if Service B can't process requests as quickly as Service A produces them?
  • Load spikes?
• What if Service B dies while processing a request?

SQS

• Simple Queue Service (SQS): A managed, distributed message queueing service frequently used to communicate between AWS services.

Guaranteeing Delivery

• Want to guarantee At-Lease-Once Delivery
  • ​Every message will be delivered
  • But, it may be delivered more than once

Message Ordering

• Ordering:
  • ​We want high throughput of messages

• Standard Queues: "Unlimited" TPS
• FIFO Queues: Max 300 TPS

Polling for Messages

• How do receivers retrieve messages from the queue?
  • Short Polling: Immediately return if no messages available. Search subset of nodes.
  • Long Polling: Wait until a message is available for processing. Searches all nodes.

Other SQS Concepts

• Retention Period: Messages are deleted from a queue if not processed within a certain amount of time (up to 14 days)
• Max Message Size: Up to 256KB per message
• Dead Letter Queue: Messages can be placed in a DLQ after failing to be deleted after a predefined number of receives

SQS Pricing

• Requests
  • Standard: 40¢ per 1M requests
  • FIFO: 50¢ per 1M requests
• Data Transfer between SQS/EC2
  • Free (if within the same region)

 

• Can return multiple messages per request
• 1 request = 64KB chunk of a payload

 

• Free Tier: 1M requests

SQS Demo

SQS Worksheet

Complete the worksheet section on SQS.