AWS SQS Core Concepts: A Beginner's Guide
Published: 2023-02-18 23:44:09

## Introduction
AWS SQS (Simple Queue Service) is a fully managed message queuing service that enables you to decouple and scale your distributed microservices and serverless applications. SQS eliminates the complexity and overhead associated with managing and operating message oriented middleware, while providing a highly scalable, reliable, and secure messaging service.

In this blog post, we will explore the core concepts of AWS SQS and their uses.

## Queues
Queues are the foundation of AWS SQS. They provide a way to store messages that are waiting to be processed by your application. A queue is a logical grouping of messages that can be processed by one or more consumers. Messages are stored in the queue until they are consumed by a consumer or until they expire. AWS SQS provides two types of queues: standard and FIFO.

## Standard Queues
Standard queues provide a highly scalable and durable messaging system for distributed systems that do not require the exact ordering of messages. Messages are stored in the order they are received, but are not guaranteed to be delivered in the same order. Standard queues provide at-least-once delivery, which means that messages can be delivered more than once, but never lost.

## FIFO Queues
FIFO (First-In-First-Out) queues provide the exact ordering of messages that is required by many applications. Messages are processed in the order in which they are received and are delivered exactly once. FIFO queues provide exactly-once processing, which means that messages are processed only once and are never duplicated.

## Messages
Messages are the payloads of data that are sent between producers and consumers. They can be any string, up to 256KB in size. Messages can contain structured data in JSON, XML, or other formats, and can also contain metadata in the form of message attributes.

## Producers
Producers are applications that send messages to a queue. A producer can be any application that has access to AWS SQS, including EC2 instances, Lambda functions, and external applications. When a producer sends a message, it specifies the queue to which the message is sent.

## Consumers
Consumers are applications that retrieve messages from a queue and process them. A consumer can be any application that has access to AWS SQS, including EC2 instances, Lambda functions, and external applications. When a consumer retrieves a message, it specifies the queue from which the message is retrieved. A queue can have one or more consumers, and each consumer retrieves and processes messages independently.

## Visibility Timeout
When a consumer retrieves a message from a queue, the message becomes invisible to other consumers for a certain period of time, called the visibility timeout. This ensures that the message is not processed by multiple consumers at the same time. If the consumer does not delete the message within the visibility timeout period, the message becomes visible to other consumers again.

## Dead-Letter Queues
Dead-letter queues are queues that receive messages that could not be processed by the main queue. These messages are called "dead-letter messages" and can be analyzed to diagnose and fix the issues that caused them to be rejected. Dead-letter queues are useful for ensuring that messages are not lost, and for troubleshooting issues in your application.

## Conclusion
In this blog post, we've covered the core concepts of AWS SQS and their uses. Queues are the foundation of AWS SQS, and messages are the payloads of data that are sent between producers and consumers. Producers send messages to a queue, and consumers retrieve messages from a queue and process them. Visibility timeouts ensure that messages are not processed by multiple consumers at the same time, and dead-letter queues are useful for troubleshooting issues in your application.