Creating an SQS Queue

Introduction

Amazon Simple Queue Service (SQS) is a fully managed message queuing service. While SNS uses a "push" model, SQS uses a "pull" (polling) model.

SQS is used to decouple microservices. If Service A generates tasks faster than Service B can process them, Service A sends the tasks to an SQS Queue. Service B then pulls tasks from the queue at its own pace, preventing it from crashing under heavy load.

Queue Types

When creating a queue, you must choose between two types:

1. Standard Queues: Offer maximum throughput, best-effort ordering, and at-least-once delivery. A message might be delivered more than once, and the order is not strictly guaranteed.
2. FIFO (First-In-First-Out) Queues: Messages are processed exactly once, in the exact order that they are sent. The tradeoff is that FIFO queues have lower throughput limits (3,000 messages per second).

Creating a Queue via CLI

To create a standard queue using the AWS CLI:

aws sqs create-queue --queue-name MyStandardQueue

The command returns a QueueUrl. You use this URL in your application code to send or receive messages.

To create a FIFO queue, you must append .fifo to the queue name and specify the FifoQueue attribute:

aws sqs create-queue \
    --queue-name MyOrderQueue.fifo \
    --attributes FifoQueue=true

Dead-Letter Queues (DLQ)

If a message cannot be processed (e.g., your consumer application throws an error every time it tries to read a malformed message), SQS will retry indefinitely by default. To prevent infinite loops, you should always configure a Dead-Letter Queue. After a message fails processing a specified number of times, SQS moves it to the DLQ so developers can analyze the bad message later without blocking the main queue.

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