Design a Payment System

1. Problem Statement

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.

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)

4. What the Interviewer Looks For

The interviewer probes these areas, and the report grades the interview against them.

• Requirements, state machine, and capacity
• Idempotency and exactly-once effects
• Ledger and source of truth
• Processor integration and uncertain outcomes
• Reconciliation, security, and resilience