A6The outbox pattern

The problem

1 s on screen = 100 ms

The order saved, but the confirmation email never came. Where did it go?

Save, then publish

App saves each order to Orders DB, then publishes an event through Broker for the receipt email.

Live metrics for each version of the scene
Metric	Dual write	Outbox	Change
	—	—	—
	—	—	—
target ≤ 400 ms	—	—	—

A6The outbox pattern

Saving to the database and publishing an event are two writes. If the second fails, the world never hears about the first.