Stripe - the case study

The whole shape at once: one card, one shopper, and every board below drawn as a single system.

Boards

Before you start. You need to know what a retry is: a computer that got no answer, so it asks again. That is the only background this note assumes; everything else about moving money starts from zero.

The idea in 30 seconds

A request can be interrupted anywhere between “sent” and “answered”, so it needs to survive being repeated by accident: that’s what an idempotency key is for.
Money isn’t a number you overwrite. It’s pairs of matching lines you only ever add to: a debit and a credit that must sum to zero.
The fix for “how do I prove where the money is” is older than computers. Venice already didn’t trust a single balance number in 1494.
“Approved” is a hold, not a transfer. The real movement of money lags the receipt by about a day or two.
Because the pieces above can still drift apart in practice, the whole system checks itself against reality every night: reconciliation.
Stripe’s product is the ledger. Taking your card is the part in front of it.

Read the story · Skip to the numbers