AWS SNS vs SQS: A Real-World Project Analysis

I worked with a growing e-commerce company that needed to handle communication between different parts of their application. They ended up looking at two AWS services: Simple Notification Service (SNS) and Simple Queue Service (SQS). Here’s what I learned from that project.

Understanding AWS SNS and SQS

AWS SNS is a pub-sub messaging service. You publish a message to a topic, and AWS fans it out to multiple subscribers simultaneously. One message, many recipients.

AWS SQS is a message queue. You send messages to a queue, and workers pull from it when they’re ready. Point-to-point, not broadcast.

The difference matters more than it sounds. Pub-sub works when you need everyone notified at once. Queues work when you need controlled, asynchronous processing.

AWS SNS and SQS:

Real Business Applications

Here is where each service makes sense:

Order Processing: An e-commerce site gets order events constantly. SQS queues these up so worker processes can handle them at their own pace without overwhelming downstream systems.

Payment Notifications: When a payment goes through, multiple systems need to know: the accounting system, email service, fraud detection, and maybe more. SNS pushes the notification to all of them at once.

Inventory Management: Instead of having systems constantly poll for stock updates, SNS can push updates to subscribed inventory systems the moment stock levels change.

Delayed Task Execution: Generating reports, running cleanup jobs, things that do not need to happen immediately. SQS holds these until a worker is ready to process them.

System Alerts: Something breaks and you need to notify the on-call team, the monitoring system, and maybe management. SNS broadcasts to all subscribed endpoints.

Examples

SQS in Action: The e-commerce company queued order messages during peak sales. When orders came in, they went into an SQS queue. Workers picked them up asynchronously, which prevented the order system from crashing under load.

SNS in Action: Payment transactions triggered SNS notifications. The accounting system, email service, and fraud detection tool all subscribed to the same topic and received payment details as they happened.

AWS SQS and SNS: A Performance Comparison

Latency

SQS: Pull-based by design. There is usually a short delay while messages sit in the queue waiting for a worker to poll. For most applications, this delay is negligible, but it is worth knowing. The benefit is you can tune polling frequency to balance latency against cost.

SNS: Push-based. AWS delivers messages to subscribers as soon as you publish. Latency is typically lower for real-time use cases.

AWS SNS vs SQS: Scalability

Both services scale automatically. SQS can handle virtually unlimited message volume. SNS topics can publish to huge numbers of subscribers. You do not really need to think about capacity planning for either service at normal scale.

AWS SNS vs SQS: Message Retention and Reliability

SQS: Messages stay in the queue for up to 14 days by default (you can configure this). If a worker crashes mid-processing, the message eventually becomes visible again for another attempt. Standard queues give you at-least-once delivery. FIFO queues give you exactly-once processing if you enable content-based deduplication.

SNS: AWS retries delivery to subscribers, but if all retries fail, the message is gone. SNS does not buffer messages long-term like SQS does. For critical messages, you often pair SNS with an SQS queue as a dead-letter destination to catch failed deliveries.

Use Case Complexity

SQS: Simple to start with. You create a queue, send messages, and consume them. Complex workflows (prioritization, filtering, dead-letter handling) require more thought and configuration.

SNS: Straightforward for broadcasting. The complexity comes when you need fine-grained filtering policies or want to route messages to different subscriber types based on message attributes.

AWS SNS vs SQS: Cost

Both use a pay-as-you-go model.

SQS: You are charged per API request (SendMessage, ReceiveMessage, DeleteMessage, and so on). High-volume applications can accumulate significant costs if you are polling frequently.

SNS: You are charged per notification published and per notification delivered. SMS and email have different pricing tiers based on destination and message size.

For most applications, the cost difference is marginal. Design for your use case first, optimize cost second.

Conclusion

For the e-commerce example: payment notifications went through SNS because accounting, email, and fraud systems all needed updates at the same time. Order processing went through SQS because workers needed to process at their own pace without stepping on each other.

Choose SNS when you need one message to trigger multiple actions simultaneously. Choose SQS when you need controlled, reliable, asynchronous processing.

Both services work well together. SNS can fan out to SQS queues, giving you the best of both patterns.