SNS vs SQS
Compare pub/sub event broadcasting with durable queue-based asynchronous processing in AWS.
Messaging
Amazon SNS
Amazon SNS is a pub/sub messaging service that pushes messages to subscribers such as email, Lambda, HTTP endpoints, or SQS queues. It is built for fan-out notification patterns.
Messaging
Amazon SQS
Amazon SQS is a durable message queue used to decouple systems and support asynchronous processing. Consumers pull messages and process them independently.
Key Differences
SNS is a publish-subscribe service, while SQS is a queue service.
SNS pushes events to subscribers, while SQS stores messages until consumers retrieve them.
SNS is used for fan-out communication, while SQS is used for buffering and decoupled background processing.
SQS is designed for durable asynchronous consumption, while SNS is designed for event distribution to multiple destinations.
SNS and SQS are often used together, especially when one event must reach multiple independent consumers reliably.
The main distinction is broadcast versus queue-based work distribution.
When to Use
When to use SNS
Use SNS when one event needs to notify multiple downstream systems, services, or subscribers in a pub/sub pattern.
When to use SQS
Use SQS when you need reliable queue-based decoupling, background work processing, retries, and controlled consumption by workers.
Tradeoffs
SNS is excellent for fan-out, but not a replacement for durable queue-based processing.
SQS is excellent for asynchronous workers, but not a replacement for event broadcasting to many subscribers.
Together they often form a stronger event architecture than either alone.
Common Mistakes
Using SNS when the real need is durable worker processing.
Using only SQS when the same event should fan out to multiple independent consumers.
Treating pub/sub and queueing as the same messaging model.
Interview Tip
A strong short answer is: SNS broadcasts, SQS queues.