SQS Vs. SNS: Choosing The Right AWS Messaging Service

Picture this. You recently shipped a new feature, and things were working smoothly — until they didn’t.

Now, one service is timing out. Another is overloaded. You dig in and realize the issue is with how your systems communicate. Messages are not arriving when or where they should.

Your team had set up Amazon SNS for notifications and Amazon SQS for processing tasks. But somewhere along the way, the difference between SQS vs. SNS (and how they’re wired together) got lost in translation.

It’s a common trap for many teams, one that introduces reliability issues, hidden costs, and serious scaling challenges.

This post is your guide to getting it right. We’ll explore how each service works, when to use SNS or SQS (or both), and what to watch out for in terms of cost, performance, and beyond.

What Does Amazon SQS Do?

Amazon Simple Queue Service (SQS) is a fully managed message queuing service from AWS. It enables decoupled, asynchronous communication between distributed components of your application.

Instead of services calling each other directly (and risking failures if one is unavailable), SQS acts as a buffer. It stores messages until the receiving system is ready to process them. This means better fault tolerance, performance, and scalability across your architecture.

How SQS works

At a high level, producers (or senders) add messages to a queue. Consumers (or workers) then poll the queue and retrieve messages for processing. Once a message is successfully handled, it’s deleted from the queue.

SQS supports two queue types:

You can also configure:

Let’s say you have an e-commerce site. When a customer places an order, the order service sends a message to an SQS queue. Downstream services, such as payment, inventory, and fulfillment, consume and process the message independently, without needing to talk to each other directly.

What Does Amazon SNS Do?

Amazon Simple Notification Service (SNS) is a fully managed publish/subscribe (Pub/Sub) messaging service. It lets you send messages from a single source to multiple subscribers. This works instantly and asynchronously.

Unlike SQS, which queues messages for individual consumption, SNS broadcasts messages to all subscribed endpoints in near real-time. It’s ideal for fan-out patterns, where one event needs to notify many different systems or services at once.

How SNS works

With SNS, publishers send messages to a topic. Subscribers (which could be SQS queues, AWS Lambda functions, HTTP/S endpoints, email addresses, or mobile devices) receive those messages almost immediately.

The key features of SNS include:

SQS Vs. SNS: These Key Differences Will Help You Decide When To Use Each (Or Both)

Let’s break down the key differences between SQS and SNS so you can make the right call for your workload.

1. Queue vs. topic architecture 

SQS follows a queue-based, point-to-point architecture. Producers send messages to a queue, where they sit until a single consumer pulls and processes them.

SNS uses a topic-based, publish/subscribe (pub/sub) architecture. When a message is published to a topic, it is pushed to all subscribed endpoints. These could be SQS queues, Lambda functions, HTTP/S endpoints, or SMS/email recipients. This is a one-to-many model.

2. Delivery pattern

SQS is pull-based. Consumers must poll the queue to fetch messages. This gives you full control over how and when messages are processed. And that is ideal for batch jobs or rate-limited services.

SNS is push-based. It automatically delivers messages to each subscriber as soon as they’re published. This enables near-real-time event propagation, which is especially handy for alerting systems or distributed triggers.

Note that SQS’s polling delay can introduce slight latency, while SNS delivers messages in milliseconds, but offers less processing control.

3. Message retention and durability

SQS is designed for guaranteed delivery. SNS assumes that subscribers are always available — unless you use it with SQS or a retry-enabled Lambda. Here is what we mean.

SQS stores messages for up to 14 days. If a consumer is offline or slow to process, the message stays in the queue. This ensures eventual delivery. SNS, on the other hand, does not retain messages by default. Once it delivers (or retries and fails), the message is gone. If the endpoint isn’t reachable, it may never receive the message.

4. Ordering guarantees

SQS Standard queues provide high throughput but don’t guarantee message order. SQS FIFO queues ensure messages are processed exactly once and in the order sent. In contrast, Amazon SNS offers no ordering guarantees. Even if messages are fanned out to FIFO queues, ordering isn’t preserved unless managed manually.

5. Fan-out support

SNS was built for fan-out. One published message can trigger dozens or even hundreds of subscribers. This pattern is ideal for event-driven architectures that require a single action to initiate multiple workflows.

For example, when a user signs up, SNS can notify:

And all from one message.

On the flip side, SQS does not support fan-out directly. Each message is delivered to a single consumer.

6. About subscribers and consumers

SQS delivers each message to only one consumer, even if multiple workers are polling. This ensures workload distribution and deduplication. However, SNS supports multiple independent subscribers. Each receives its own copy of the message. This makes SNS ideal for parallel processing across systems.

7. Retry and Dead-Letter Queue (DLQ) support

SQS has native support for DLQs and fine-grained retry settings. If a message fails to process after X attempts, it moves to a DLQ for later inspection.

SNS handles retries differently. For HTTP/S endpoints and Lambda, SNS will retry delivery with exponential backoff. DLQs are only supported for Lambda subscribers, not for others, like email, SMS, or HTTP.

Also, note that there’s no native DLQ for SNS to HTTP subscribers. So, be sure to pair SNS with SQS if message durability is crucial.

8. Differences in cost models

SQS charges per request (Send, Receive, Delete) and per GB of data transferred. FIFO queues cost more than Standard.

Amazon SNS charges per publish request and per delivery, depending on the protocol. For example, delivering to SQS or Lambda is low-cost, SMS and mobile push notifications are more expensive, and data transfer charges may apply across regions or outside AWS. See our in-depth guide to Amazon SNS pricing here to avoid cost gotchas.

But what if you need both? Some of the most resilient AWS architectures pair SNS and SQS together. Here’s what you need to know.

Can You Use SNS And SQS Together (And Should You)? 

You can combine the pub/sub capabilities of SNS with the durability and processing control of SQS.

When you connect an SQS queue to an SNS topic, the queue becomes a subscriber. Every time a message is published to the SNS topic, a copy is automatically delivered to the SQS queue. From there, the message is retained until a consumer retrieves and processes it.

You can subscribe multiple SQS queues to the same topic. It would enable a single event to trigger multiple independent workflows. This pattern is known as fan-out with persistence.

Let’s say a user uploads a file. 

The upload service publishes an event to an SNS topic. Three different SQS queues are subscribed:

Each system gets the same message, processes it independently, and can retry if needed — all without interfering with one another.

Why use SNS and SQS together?

Here’s what you gain by combining them:

However, to make this pattern work smoothly, you’ll want to keep these best practices in mind.

Best practices to apply immediately when using SNS with SQS

Consider these:

That said, you’ll not always want to use both together.

When not to combine SNS and SQS

SNS + SQS is a powerful combo, but in some cases, it’s overkill:

Now, choosing between Amazon SQS vs. SNS will affect how your services communicate, how quickly your systems respond to events, and how much you end up spending on messaging infrastructure. Here’s how to proceed.

Tips For Choosing The Right AWS Messaging Tool

Consider the following key questions, decision points, and tradeoffs to inform your decision.

Identify your message delivery pattern

Start by asking:

Do you need to send a message to one service or multiple services at once?

If you need one-to-one, go with SQS. And if you need one-to-many? Use SNS or SNS to SQS fan-out pattern. If you need both, use SNS to publish events and SQS queues to deliver those messages reliably to each service.

Evaluate your durability requirements

Can you afford to lose a message, or must every message be processed, no matter what

If durability is critical, go with SQS (messages are stored and retried). But if loss is acceptable (such as alerts and metrics), using SNS alone may suffice.

Consider ordering and Exactly-Once Delivery

Does the order in which messages are processed matter to me?

If yes, (financial transactions, inventory updates, state transitions in workflow engines), then use SQS FIFO queues. If not, pick Standard SQS or SNS.

SNS does not guarantee ordering (even when publishing to FIFO queues) unless you carefully manage message groups and sequence IDs.

Define processing behavior

Do you need full control over how and when a message is processed?

SQS gives you that control. You can batch messages, delay processing, and use visibility timeouts. You can also configure retries and DLQs, and throttle consumers based on load.

SNS, on the other hand, pushes messages immediately. If a subscriber fails, SNS retries based on protocol settings. You have less fine-grained control.

Assess scalability and fan-out needs

Do you expect multiple systems to respond to the same event?

SNS is built for that. You can fan out messages to dozens of endpoints, add new subscribers without changing the publisher, and easily integrate mobile, serverless, or legacy systems.

If you’re building an event-driven architecture, SNS to SQS (or Lambda) is a highly scalable and resilient pattern.

Think cost efficiency

While both services are “cheap” at low scale, their cost profiles grow differently.

That means a single event to five SNS subscribers translates into 5X the delivery cost. If those subscribers are SQS queues, you also pay for SQS usage on top of SNS.

To avoid cost surprises, use a reliable platform like CloudZero to track how messaging usage impacts your AWS bill. You’ll be able to allocate those costs to specific teams, products, or customers, like this:

More on that shortly.

Account for compliance or audit requirements

Do you need to track, inspect, or audit all message processing attempts?

If so:

This is especially useful in finance, healthcare, and other regulated industries.

Next up, we’ll see how to keep all this scalable without losing track of costs, especially when fan-out patterns multiply messaging usage behind the scenes.

How To Catch, Control, And Optimize Your SQS And SNS Spend With Cost Confidence

If you’ve made it this far, one thing is clear: SQS and SNS solve distinct problems, and often work better together. But as your architecture scales, so can your AWS bill, especially when you’re using fan-out patterns and multiple queues or triggers.

With CloudZero, you’ll know exactly where your messaging costs come from and how to reduce them without compromising performance. Without endless tagging or Cost Explorer exports. You can spot cost anomalies in real time, investigate root causes, and prevent surprise costs before your next invoice pings.

CloudZero gives you the cost visibility AWS doesn’t. It helps your team answer tough questions like:

That means more control, less waste, and better margins, without sacrificing scalability or performance.

That’s how teams at Skyscanner, Expedia, and MalwareBytes stay in control. You can, too — and you don’t need perfect tagging or dashboards to get there. Instead, to see how the best use SQS and SNS with total cost confidence — so you can, too.