Why do projects choose Kafka, and why RabbitMQ? What do they rely on when selecting a message broker?

The choice between Kafka and RabbitMQ depends on the project requirements and the specifics of the tasks:

• Kafka is chosen when high throughput, load resilience, the ability to store large volumes of data, and real-time stream processing are needed. Kafka is well-suited for analytics systems, logging, event sourcing, where scalability and message history preservation are important.

• RabbitMQ is preferred for traditional message queuing with support for complex routing, delivery acknowledgments, priorities, and when routing flexibility (e.g., using exchange types) is important. RabbitMQ is easier to set up for conventional queue tasks and integrations.

When selecting a broker, consider:

• Performance and scalability requirements
• Delivery reliability and guarantees (at-least-once, exactly-once)
• Routing complexity and support for various messaging patterns
• Ecosystem and integrations with other services
• Operational costs for support and monitoring

Thus, Kafka is for scalable streaming platforms, while RabbitMQ is for flexible, traditional queues with diverse routing scenarios.