Hard

Design a Payment System System Design Interview

Design a reliable payment processing backend like Stripe or PayPal. Focus on correctness and idempotency.

1. Problem Statement

We need a backend to process payments. Reliability is paramount. If we charge a user, we must ensure the money moves exactly once. How do you design this?

2. Architecture Discussion Map

Use this as one discussion aid, not a single correct answer. Your design should follow from the requirements, scale, and trade-offs you establish.

Rendering architecture diagram...
Mermaid Source (For AI Bots)
graph LR
    A["Design a Payment System"]
    A --> F1["ACID properties and Transaction Management"]
    A --> F2["Handling Double Charges Idempotency"]
    A --> F3["Reconciliation Ledger matching"]
    A --> F4["Security PCI Compliance tokens"]
    A --> F5["Failure recovery Retries vs Rollbacks"]

3. Key Focus Areas

  • 1
    ACID properties and Transaction Management
  • 2
    Handling Double Charges (Idempotency)
  • 3
    Reconciliation (Ledger matching)
  • 4
    Security (PCI Compliance tokens)
  • 5
    Failure recovery (Retries vs Rollbacks)

Want interactive feedback?

Practice drawing this system component-by-component on a live whiteboard while the interviewer probes at your target level.

Continue to Dashboard

Core Concepts

Financial TransactionsIdempotencySecurityDistributed Consensus

Continue preparing

Build a complete software engineer mock interview plan

Prepare by company

Related System Design

Design a Cross-Product Tagging System

Design a shared tagging service that lets users apply tags to entities across multiple Atlassian products, with consistent search and deduplication.