System Design · Senior · Question 51 of 75

Is "exactly-once" message delivery achievable in a distributed system?

✓Correct answer: Not as delivery over unreliable networks; in practice you get at-least-once delivery plus idempotent or deduplicated processing ("effectively once")
2Yes, every message queue guarantees it by default
3Yes, if you use HTTPS

Explanation

Brokers that advertise exactly-once rely on transactions and dedup within their boundaries; side effects outside still need idempotency.

Further reading

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