Message Queues and Event Streaming

Broker queues (RabbitMQ, SQS) hand each message to one worker, wait for an ack, and delete it: built for distributing jobs. Event logs (Kafka) append events to a durable, partitioned log that many consumer groups read independently at their own offsets, with replay for free. Ordering holds only within a partition, and 'exactly-once' in practice means at-least-once delivery plus idempotent consumers. Applied-AI interviews probe it because ingestion pipelines, async inference jobs, and feedback events all hang off one of these two primitives, and picking the wrong one is expensive to undo.