Kafka vs MQTT: What are the differences?

Apache Kafka and MQTT are two widely used messaging protocols. Let's discuss the key differences between them:

1. Scalability and Performance: Kafka is designed to handle high-volume, real-time data streams and provides high throughput and low latency. It is horizontally scalable and can handle millions of messages per second. On the other hand, MQTT is a lightweight protocol that is primarily designed for low-bandwidth, constrained devices. It is built for reliable communication over unreliable networks and is suitable for IoT applications with limited resources.

2. Message Delivery Guarantees: Kafka guarantees both at-least-once and at-most-once message delivery semantics. It achieves this through configurable settings and the use of message offsets. On the contrary, MQTT offers three quality of service (QoS) levels: QoS 0 (at-most-once), QoS 1 (at-least-once), and QoS 2 (exactly-once). This allows MQTT to provide more flexibility in terms of reliability based on the specific requirements of the application.

3. Message Persistence: Kafka is a distributed commit log that stores all messages for a configurable retention period. This enables data replayability and fault tolerance. MQTT, on the other hand, does not persist messages by default. While some MQTT brokers may support message persistence, it is not a guaranteed feature like in Kafka.

4. Publish-Subscribe Model: Kafka follows a publish-subscribe (pub-sub) messaging model where messages are published to topics and consumers subscribe to these topics to receive messages. MQTT also supports a similar pub-sub model, but it allows for more granular control through the use of MQTT topics and filters. MQTT topics can be used for specific message routing, filtering, and subscribing.

5. Client Libraries and Ecosystem: Kafka offers robust client libraries and has a rich ecosystem of connectors and tools, making it well-suited for building data-intensive streaming applications. It has extensive support for different programming languages and provides high-level abstractions for stream processing. MQTT also provides client libraries for various programming languages, but its ecosystem is not as extensive as Kafka's, especially in terms of analytics and stream processing frameworks.

6. Integration with IoT: MQTT is often preferred for IoT applications due to its lightweight nature and efficient use of network bandwidth. It is widely adopted in IoT platforms and is supported by many embedded devices. Kafka, on the other hand, can also be used in IoT scenarios but is typically favored for high-throughput, real-time processing and analytics use cases where data volume and ingestion rate are critical factors.

In summary, Kafka is a scalable, high-performance messaging system with strong durability guarantees and extensive ecosystem support, while MQTT is a lightweight, reliable protocol designed for IoT applications with limited resources and network constraints.