Messages may be lost but are never duplicated. Achieved by: acks=0 (no confirmation), or acks=1 without retries. The producer fires and forgets. If the leader crashes after receiving but before writing, the message is gone. Use case: metrics, telemetry, log aggregation where occasional data loss is acceptable and throughput is paramount.
Key configuration
acks=0
retries=0
enable.auto.commit=true — commit before processing