Amazon SNS vs Amazon SQS: What are the differences?

Introduction

Amazon Simple Notification Service (SNS) and Amazon Simple Queue Service (SQS) are both messaging services provided by Amazon Web Services (AWS). They are designed to help developers build scalable, decoupled, and fault-tolerant applications.

1. Message Distribution Model:

Amazon SNS uses a publish-subscribe (pub/sub) messaging model, where a single message is delivered to multiple subscribed endpoints. On the other hand, Amazon SQS uses a distributed queuing model, where messages are stored in a queue and processed by consumers at their own pace.

2. Message Retention:

In Amazon SNS, messages are not retained. Once a message is published, it will be delivered to the subscribed endpoints, or discarded if the endpoints are not available. In contrast, Amazon SQS retains messages in a queue until they are explicitly deleted by the consumer.

3. Message Duplication:

Amazon SNS may deliver duplicate messages in certain failure scenarios, but it provides built-in support for deduplication using message attributes. On the other hand, Amazon SQS ensures that each message is delivered at least once and does not deliver duplicates, making it suitable for applications that require strict message ordering.

4. Subscription Protocols:

Amazon SNS supports various subscription protocols such as HTTP/HTTPS, email, SMS, Lambda, and more. It allows flexibility in reaching different types of endpoints. In contrast, Amazon SQS only supports messaging via HTTP/HTTPS.

5. Pricing Model:

Amazon SNS charges based on the number of messages published and the number of API requests made. Amazon SQS charges based on the number of messages transferred in and out of the queue, as well as the number of API requests made.

6. Message Fanout and Delivery Time:

Amazon SNS enables immediate message fanout to multiple subscribers, providing near-real-time message delivery. Amazon SQS, being a queue-based service, offers a delay feature to control the delivery time of messages.

In summary, Amazon SNS uses a pub/sub model, allows various subscription protocols, and incurs charges based on messages published, while Amazon SQS uses a queuing model, supports only HTTP/HTTPS messaging, and charges based on messages transferred.