Choosing between Apache Kafka and Amazon SQS: A developers' guide

Both are proven solutions for handling asynchronous communication, each designed to solve specific engineering challenges. While Kafka excels as a distributed event streaming platform with high throughput, SQS shines as a fully managed message queue service.

Let's dive into their architectural differences and understand when to use each one.

Why do these tools matter?

In this blog post, we're focusing on two types of data: notifications that trigger immediate actions and events that capture state changes. Both need to be processed reliably at scale. Consider these scenarios:

Notifications:

• Push notifications to millions of mobile devices

• Alert systems triggering incident responses

• Payment confirmation emails to customers

Event Streams:

• User behavior events for real-time analytics

• Financial transactions for fraud detection

• Order status changes in e-commerce systems

These systems need robust message handling that can scale with your architecture. While notifications often require guaranteed delivery to specific consumers, events might need to be processed by multiple downstream systems or replayed for analysis. This is where Kafka and SQS offer different approaches to solve these challenges.

The core difference: Message delivery models

Think of SQS as a postal delivery system and Kafka as a radio broadcast network. With SQS, when someone sends a message, it sits in a queue until one recipient collects it. With Kafka, messages are like radio programs - they're broadcast on a channel (called a topic), and multiple listeners can tune in simultaneously.

Quick feature comparison

When to choose Amazon SQS?

SQS is your friend when:

• You want a simple, managed message queue without infrastructure headaches

• Your messages need to be processed by exactly one consumer

• You're already using AWS services

• You need a quick setup and don't want to manage servers

• Your message volume is moderate

• You need automatic scaling without managing infrastructure

For example, imagine you're building a food delivery app. When a customer places an order, you might use SQS to queue the order for processing. One delivery agent picks up each order, and once it's picked up, no other agent should see it.

When to choose Apache Kafka?

Kafka shines when:

• You need real-time data streaming and analytics

• Multiple systems need to consume the same messages

• You need to store message history for replay

• You're handling high-volume data (like logs or metrics)

• You need fine-grained control over your setup

• You need to process data streams in real-time for immediate insights

• Your system requires low-latency data processing

Think of a social media platform's notification system. When a celebrity posts something, millions of followers need to be notified. Kafka would be perfect here because one message needs to reach many consumers, and the system needs to handle high volume in real-time.

Real-world examples

SQS Example: An e-commerce website using SQS to handle order processing. When a customer places an order, it goes into a queue. One worker picks it up, processes the payment, and removes it from the queue. Simple and effective.

Kafka Example: A stock trading platform where market data streams through Kafka, enabling multiple systems (trading algorithms, risk analysis, monitoring, compliance) to process each market tick simultaneously. This real-time parallel processing is crucial for making split-second trading decisions.

Understanding message persistence

One key difference between these systems is how they handle message storage:

SQS: Messages are retained for up to 14 days, after which they're automatically removed. This suits use cases where messages are transient and only need short-term storage, like processing user requests or handling application events.

Kafka: Messages can be stored indefinitely based on your configuration. This makes Kafka excellent for scenarios where you might need to replay old messages or analyze historical data patterns.

Scalability considerations

Both systems scale differently:

SQS: Automatically scales based on demand. AWS handles all the infrastructure scaling behind the scenes. Perfect for variable workloads where you don't want to manage scaling yourself.

Kafka: Scales by adding more brokers to your cluster. While this requires more hands-on management, it allows for massive scale and fine-tuned performance optimization. Kafka can handle millions of messages per second when properly configured.

Making your choice

Ask yourself these questions:

• What's your message delivery model - do you need to notify one consumer (like sending an order to a single processor) or multiple consumers (like broadcasting user activity to analytics, audit, and recommendations)?

• What's your operational model - can you invest resources in managing infrastructure, maintaining codebase, or do you need to focus on building features?

• What's your scale - are you handling occasional notifications or processing a constant stream of user events?

• Do your business requirements include analyzing historical data or replaying past events (like fraud detection or audit trails)?

• Does your business need real-time insights from your data (like live dashboards or instant analytics)?

• Is the sequence of messages critical for your business logic (like processing financial transactions or maintaining state order)?

Recommended Read: How building a notification system in-house can be really expensive?

Key takeaway

Both tools are excellent at what they do, but they serve different purposes:

• Choose SQS when you want a simple, managed queue service that's easy to set up and maintain. It's perfect for decoupling applications and handling moderate message volumes without infrastructure overhead.

• Pick Kafka when you need a robust platform for real-time data streaming, high-throughput messaging, or when multiple systems need access to the same data streams. It's ideal for building data pipelines and real-time analytics applications.

Remember, you can even use both in the same system - SQS for simple queuing needs and Kafka for real-time streaming requirements.