2 min lesson
Delivery semantics: the trade-off you must name
Explain the contrast in "Delivery semantics: the trade-off you must name", then make the decision rule clear.
Step 1 of 3
Delivery semantics: the trade-off you must nameexactly-once is mostly idempotency in disguise
At billions of events a day, true end-to-end exactly-once is expensive and often unnecessary. The pragmatic pattern is at-least-once delivery plus idempotent writes, so duplicates are guaranteed to arrive but harmless because the write path collapses them.
Interactive diagram. Tab through its regions; each focused region shows its detail in the panel below.
diagram: compare
Pick the default for the firehose; reserve the stronger guarantee for flows where a dup is a real error.