Amazon Simple Queue Service (SQS) is a fully managed message queuing service that enables you to decouple and scale microservices, distributed systems, and serverless applications. SQS eliminates the complexity and overhead associated with managing and operating message oriented middleware, and empowers developers to focus on differentiating work.
With SQS, you can send, store, and receive messages between software components at any volume, without losing messages or requiring other services to be always available. SQS makes it simple and cost-effective to decouple and coordinate the components of a cloud application.
SQS offers two types of queues, Standard and FIFO (First-In-First-Out). Standard queues offer best-effort ordering, which ensures that messages are generally delivered in the order in which they are sent. FIFO queues guarantee that messages are processed exactly once, in the order that they are sent, and they are designed to prevent duplicates.
Amazon Simple Notification Service (SNS) is a fully managed messaging service that enables you to send messages to multiple subscribers or endpoints. SNS supports multiple protocols including HTTP, HTTPS, email, and Lambda, and it can be used to send push notifications to mobile devices, or to process messages asynchronously using AWS Lambda.
SNS allows you to send a message to a "topic" which is a logical access point and communication channel. Subscribers can then subscribe to that topic to receive the messages.
SNS also provides a feature called fan-out delivery, which enables messages to be delivered to multiple subscribers in parallel, this allows SNS to handle high-throughput and burst traffic, and can improve the overall performance of your application.
MassTransit uses SNS to route published messages to SQS queues.