Common Problems
Payment System
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Understanding the Problem
📸 What is Stripe?
Payment processing systems like Stripe allow business (referred to throughout this breakdown as merchants) to accept payment from customers, without having to build their own payment processing infrastructure. Customer input their payment details on the merchant's website, and the merchant sends the payment details to Stripe. Stripe then processes the payment and returns the result to the merchant.
Functional Requirements
Core Requirements
- Merchants should be able to initiate payment requests (charge a customer for a specific amount).
- Users should be able to pay for products with credit/debit cards.
- Merchants should be able to view status updates for payments (e.g., pending, success, failed).
Below the line (out of scope):
- Customers should be able to save payment methods for future use.
- Merchants should be able to issue full or partial refunds.
- Merchants should be able to view transaction history and reports.
- Support for alternative payment methods (e.g., bank transfers, digital wallets).
- Handling recurring payments (subscriptions).
- Payouts to merchants.
Non-Functional Requirements
Before defining your non-functional requirements in an interview, it's wise to inquire about the scale of the system as this will have a meaningful impact on your design. In this case, we'll be looking at a system handling about 10,000 transactions per second (TPS) at peak load.
The Set Up
Defining the Core Entities
API or System Interface
High-Level Design
1) Merchants should be able to initiate payment requests
2) Users should be able to pay for products with credit/debit cards.
3) The system should provide status updates for payments
Potential Deep Dives
1) The system should be highly secure
2) The system should guarantee durability and auditability with no transaction data ever being lost, even in case of failures.
3) The system should guarantee transaction safety and financial integrity despite the inherently asynchronous nature of external payment networks
4) The system should be scalable to handle high transaction volume (10,000+ TPS)
Servers
Kafka
Database
Bonus Deep Dives
1) How can we expand the design to support Webhooks?
Final Design
What is Expected at Each Level?
Mid-level
Senior
Staff+
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