Delivery semantics
On This Lesson 4 topics
This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.
In this lesson
explain the three guarantees and the exactly-once limit.
Planned topics
- At-most-once: send and forget; messages may be lost, never duplicated.
- At-least-once: retry until acknowledged; no loss, but duplicates are possible. The usual default.
- Exactly-once delivery across systems is not achievable end to end, because an acknowledgment can be lost (MID-023).
- Effectively-once: at-least-once delivery plus idempotent processing (or deduplication), so repeats have no extra effect.
- Some platforms offer exactly-once processing within their own boundary (for example Kafka transactions); verify scope before relying on it.
Draft outline details
Demonstration
timeline: consumer processes, ack lost, broker redelivers, the consumer sees the message twice.
Check your understanding
How do you get effectively-once?
Show answer
At-least-once delivery plus idempotent handling.
Practice
Apply this lesson with the module's lab, exercises and quiz.
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