At-Least-Once Delivery

A practical example

Example: a registration event is processed, but its acknowledgement is lost. The queue delivers it again. The consumer checks the event identifier and returns the previous result instead of creating another registration activity.

What to evaluate before investing

• Verify when a message is acknowledged and which failures the durability contract covers.
• Ask about retry limits, retention, dead-letter handling and recovery of exhausted messages.
• Test duplicate delivery with downstream writes and confirm the intended idempotency behavior.

Limitations and tradeoffs

Real services may stop retrying or expire messages according to their configuration.

At-least-once terminology must be read alongside those limits, monitoring and recovery procedures; it is not a promise that every business action will eventually finish.