Compare Kafka and RabbitMQ. When would you use each?

Kafka: distributed log, high throughput (millions/sec), persistent storage, replay capability, consumer groups, ordered within partition. Best for: event streaming, log aggregation, real-time analytics. RabbitMQ: traditional message broker, flexible routing (exchanges, queues), message acknowledgment, lower latency for small messages. Best for: task queues, RPC, complex routing. Kafka: more operational complexity, larger infrastructure. RabbitMQ: easier setup, better for simpler use cases. Consider: throughput needs, data retention, exactly-once requirements.