Design a payment system

Advanced60 minBuilds Payment System (Stripe-style)Read first: 17.2 Safe effects and isolation, 20.3 The outbox and inbox patterns, 10.2 Delivery guarantees and idempotent consumers

STEP 1 OF 13

The brief

You are designing the payment system behind an online marketplace. A merchant's checkout asks you to charge a customer; you charge the card through an external payment provider (Stripe, Adyen, a bank's gateway), record what happened, and tell the merchant. Finance needs every cent accounted for.

How big it is

Payment requests at peak: 800 / second
Status reads: 2,000 / second
Provider throughput: about 1,000 charges / second per account
Provider latency: about 120 ms, sometimes 10+ s
p99 goal for accepting a payment: under 300 ms

What makes payments tricky

Everyone retries. Browsers, merchants' servers, your queue and your workers all retry on timeouts. Each retry is a chance to charge twice.
Timeouts hide the outcome. When a provider call times out, the card may or may not have been charged.
Providers fail. They slow down, rate-limit you and have outages, and you can't fix them.
Money must add up. Every charge, fee and refund must be recorded so that balances can be explained and matched against the provider's reports.

All changes saved

0 components · 0 connections

A blank canvas. A better system.

Add components from the palette, then drag between them to connect the request and event flow.

React Flow

Design a payment system

Advanced60 minBuilds Payment System (Stripe-style)Read first: 17.2 Safe effects and isolation, 20.3 The outbox and inbox patterns, 10.2 Delivery guarantees and idempotent consumers

STEP 1 OF 13

The brief

How big it is

Payment requests at peak: 800 / second
Status reads: 2,000 / second
Provider throughput: about 1,000 charges / second per account
Provider latency: about 120 ms, sometimes 10+ s
p99 goal for accepting a payment: under 300 ms

What makes payments tricky

Everyone retries. Browsers, merchants' servers, your queue and your workers all retry on timeouts. Each retry is a chance to charge twice.
Timeouts hide the outcome. When a provider call times out, the card may or may not have been charged.
Providers fail. They slow down, rate-limit you and have outages, and you can't fix them.
Money must add up. Every charge, fee and refund must be recorded so that balances can be explained and matched against the provider's reports.

All changes saved

0 components · 0 connections

A blank canvas. A better system.

Add components from the palette, then drag between them to connect the request and event flow.

React Flow