Designing a Scalable Payment System

Designing a payment system requires high consistency, reliability, and security. In this article, we'll design a high-level architecture for processing payments.

Core Concepts

1. Idempotency: Ensure that retries do not result in double charging.
2. ACID Transactions: Using a relational database for financial records.
3. Asynchronous Processing: Using message queues to decouple services.

Interactive System Playground

Experience the flow of a modern payment system in real-time. Click on components to learn their roles or start a simulation to see how a transaction travels from the client to the database and beyond.

Architecture

Here is the high-level architecture of our payment system:

Payment Flow

1. Client sends a payment request with a unique idempotency key.
2. API Gateway routes it to the Payment Service.
3. Payment Service checks the database if this idempotency key was already processed.
4. If not, it creates a pending payment record.
5. It calls the external payment provider.
6. Once the payment succeeds, it updates the database and publishes a "Payment Succeeded" event to Kafka.
7. Notification Service picks up the event and sends an email to the user.

This architecture ensures reliability and scale.