At-most-once means messages are delivered zero or one time. You might lose messages but never see duplicates.
How it works:
Acknowledge the message before processing. If processing fails, the message is already gone.
Use cases:
- Non-critical metrics and telemetry
- Logs where occasional loss is acceptable
- High-throughput, low-value events
Trade-off: Lowest latency and highest throughput, but you must accept data loss during failures.