.NET Architecture & System Design Interview Question #42

What is at-most-once message delivery?

Caching, CDN, Queues & Asynchronous Processing Junior Beginner

Quick Interview Answer

At-most-once delivery means a message is delivered zero or one time. The system avoids duplicate delivery, but a message can be lost if a failure occurs before or during processing.

Detailed Explanation

At-most-once delivery means a message is delivered zero or one time. The system avoids duplicate delivery, but a message can be lost if a failure occurs before or during processing.

This model can be acceptable for non-critical telemetry or operations where occasional loss is preferable to duplicate effects. Business-critical workflows usually require stronger handling.

Code Example

Deliver once
   |
failure before completion
   |
message may be lost
(no retry that creates duplicates)