Amazon SQS vs SNS: A Friendly Guide to Choosing the Right Service

Amazon SQS vs SNS: A Friendly Guide to Choosing the Right Service


Ever wondered how to pick between Amazon SQS and SNS for your project needs?

This post aims to clarify the unique purposes of Amazon Simple Queue Service (SQS) and Amazon Simple Notification Service (SNS). They might sound similar, but they serve different roles.

When you finish reading this article, you'll know which service is right for your needs. We'll look at real-life examples to show how SQS and SNS can help solve different problems in cloud communication.


This article focuses on the problems SQS and SNS solve. It doesn't focus on how they work in-depth. I strongly recommend the book AWS Fundamentals if you really want to learn AWS. I read it and loved it myself. It dives deep into both SQS and SNS.


High Demand Problem

An online ticket-selling website has a big problem during popular events. When tickets for famous events go on sale, a huge number of users visit the platform at the same time.

This leads to:

  1. Overwhelming Requests: A lot of bookings come in at once, making the server too busy and going beyond what it can handle.

  2. Order Integrity Issues: It's hard to make sure tickets are sold fairly, on a first-come-first-served basis. This can lead to selling too many tickets or double bookings.

  3. Performance Downturn: The server risks slowing down or crashing under the heavy load, impacting overall user experience.

  4. Scalability Strain: The platform struggles to efficiently scale in response to sudden demand spikes.

Introducing a Queue

When systems get too many requests, like in our ticketing platform example, using a queue can help. But what is a queue in computer systems, and how does it make things better?

A queue is an easy but strong idea where incoming data, like user requests, are put in a certain order, usually "first in, first out" (FIFO). This means the first request in the queue is the first to be handled. Think of it like a line of people waiting to buy tickets at a ticket counter. The first person in line is the first to be helped.

In technical terms, a queue acts as a buffer between the user requests and the server processing these requests. Instead of all requests hitting the server simultaneously, they are stored in a queue. The server then processes them one by one, or in small batches, at a pace it can handle without getting overwhelmed. This helps in several ways:

  1. Managing Traffic Spikes: When there's a lot of demand, like in our ticket sale example, a queue takes in the flood of requests so the server doesn't get overwhelmed.

  2. Ensuring Fair Processing: Using the FIFO principle, a queue makes sure that requests are handled in the order they come in, keeping things fair.

  3. Improving System Stability: A queue lowers the chance of system crashes by controlling the number of requests sent to the server.

  4. Scalability: Queues enable systems to handle varying loads efficiently, scaling up or down as needed.

Using a queue, our ticketing platform can handle many ticket requests at once, processing them one by one, while keeping the system stable and the order of requests organized.

SQS as the solution

Amazon Simple Queue Service (SQS) is a powerful tool for handling our ticketing platform's issues. It's a service that manages messages or requests, making sure everything runs smoothly. Here’s how SQS helps:

  1. Traffic: SQS can handle lots of ticket requests at once. It puts them in a line, so the server doesn't get too many at the same time. This stops the server from getting overwhelmed when too many people try to buy tickets.

  2. Order: SQS has a special way (FIFO queue) to make sure ticket requests are dealt with in the order they come in. This is important to sell tickets fairly.

  3. Scalability: SQS can adjust to handle more or fewer requests easily. Whether it's a normal day or a very busy day, SQS can manage without needing extra setup.

  4. Reliability: SQS keeps messages safe. Even if there's a problem in the system, no ticket requests are lost. This means the process keeps going smoothly.

  5. Integration: SQS is easy to use, especially if you're already using other AWS services. It fits right in, taking away the hassle of managing message queues.

With SQS, the ticketing platform can process lots of requests properly. This makes the system reliable and keeps customers happy.


Stock Level Update Challenge in E-Commerce

Imagine an online store that sells various products. This store has several parts: a website for customers, a stock management system, and a notification system for updates.

They face a major challenge when product stock levels change:

  1. Immediate Updates: When a product's stock changes (like when items are nearly out of stock), it's important to update the website quickly so customers see the right information. The stock management system and the customer notification system also need this update at the same time.

  2. Delayed Responses: Currently, each system is updated one by one. This method is slow and sometimes causes delays, leading to customers seeing incorrect stock information on the website.

  3. Handling Many Updates: Sometimes, stock levels change frequently, especially for popular items. The existing setup struggles to update all systems quickly, leading to confusion and potential errors.

  4. Important Alerts to Customers: Customers need to know right away when a product is back in stock or almost sold out. The current delay means customers might miss the chance to buy what they want.

  5. Complex System Maintenance: Keeping each part of the store updated separately is complicated and takes a lot of effort.

In this case, a basic queuing system isn't ideal because it doesn't update everything simultaneously. The store needs a solution that can quickly send the same message, such as a stock update, to different systems at the same time.

Introducing Pub/Sub System

To solve the challenges faced by our e-commerce platform, especially in updating multiple systems and notifying customers in real time, we turn to the concept of a Publish/Subscribe (Pub/Sub) system. But what exactly is a Pub/Sub system, and how does it differ from a queue system like SQS?

In a Pub/Sub model, a publisher sends a message to a topic, rather than directly to a specific receiver.

Various subscribers who are interested in updates from that topic subscribe to it. Whenever there's a new message, all subscribers to that topic receive the message simultaneously. This model is particularly useful in scenarios where information needs to be broadcasted to multiple recipients at once.

Solving the E-Commerce Challenge with Pub/Sub

  1. Simultaneous Updates: In our e-commerce example, once the stock level changes, the Pub/Sub system ensures that all relevant components (like the website, stock management, and customer notifications) are updated at the same time.

  2. Efficiency: Unlike direct API calls to each system, Pub/Sub distributes the message in one go, reducing the time and complexity involved in sending out multiple updates.

  3. Scalability: The Pub/Sub model effortlessly scales to handle a large number of subscribers, which is crucial during peak traffic times on the e-commerce platform.

  4. Real-Time Notifications: Customers receive timely updates, like restock alerts, almost instantly, enhancing their shopping experience.

  5. Simplified Architecture: Pub/Sub simplifies the system architecture by removing the need for each component to be aware of others. This separation reduces system complexity and enhances maintainability.

How It Differs from SQS

While SQS is a queue system designed for decoupling components and processing messages in order, a Pub/Sub system is about broadcasting messages. SQS is ideal when you need to ensure that a message is processed once and only once in a specific order. On the other hand, Pub/Sub is best when you need to send the same message to multiple recipients efficiently and simultaneously.

By introducing a Pub/Sub system, our e-commerce platform can address its notification and update challenges more effectively and maintain real-time sync across all its components.

SNS as the solution

Amazon Simple Notification Service (SNS) is a perfect fit for our online store's notification challenges. SNS is a messaging service that's really good at sending a lot of messages quickly to many different places.

Here’s how SNS solves our store's specific problems:

  1. Quick Updates to Everyone: SNS can send updates fast to all parts of our store and to our customers all at the same time. For example, when the amount of a product in stock changes, SNS makes sure this information reaches the website, stock management, and customers right away.

  2. Messages in Different Ways: SNS is great because it can send messages through various channels. It can send emails, SMS (text messages), or messages directly to our website or apps. This is super helpful for our store because we need to talk to our customers in different ways, depending on what they prefer.

  3. Dealing with Busy Times: SNS is built to handle a lot of messages, which is just what we need, especially when we have big sales or events. It makes sure that all messages are sent out and none get missed or delayed, no matter how busy it gets.

  4. Easy to Add to Our System: Adding SNS to our existing setup is straightforward. This is good because it helps us keep things simple, and it’s easier to make changes or upgrades as our store grows. It’s like adding a new tool to our toolbox that works well with the tools we already have.

  5. Cost-Effective and Efficient: Using SNS is a smart way to save money because we only pay for the messages we send. There's no need to spend money on extra equipment or software. This is especially important for our business as we want to keep our costs down while still being able to do a lot.

  6. Reliable and Secure: SNS is known for being reliable, which means it sends messages without errors or problems. It’s also secure, so we know our store's and customers' information is safe when sending messages.

Using Amazon SNS, our online store efficiently updates everyone on product availability, ensuring customer satisfaction and smooth operations by synchronizing information across the website and stock system.


In this post, we've explored how Amazon SQS and SNS serve different, yet essential roles in cloud communication.

SQS: We learned that SQS, as a queue service, effectively handles many requests in an organized way. It's perfect for situations like our ticketing platform, where managing lots of requests without overwhelming the system is important.

SNS: In contrast, SNS works great as a publish/subscribe service, ideal for sending messages to many subscribers at once. It's perfect for situations like our e-commerce platform, where fast, wide-reaching updates are important.

Knowing these differences helps you pick the right tool for your AWS needs. Both SQS and SNS are strong in their own ways, making sure your apps stay scalable, reliable, and efficient.