Design a 3-day online donation system
Company: DoorDash
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
## System Design: 3-day donation campaign
Design an online donation system for a **3-day fundraising campaign**.
### Requirements
- Users can donate money to a campaign during the 3-day window.
- Support common payment methods (e.g., credit card, Apple Pay) via a third-party payment processor.
- Show donors a confirmation/receipt.
- Provide an admin/organizer view to track total donations over time.
### Scale & reliability assumptions
- Traffic spikes heavily during the final hours (e.g., 100× normal).
- Must not double-charge donors.
- System should tolerate retries/timeouts from clients and the payment provider.
### Nice-to-haves (if time)
- Top donors / recent donations feed.
- Fraud/spam prevention.
- Refunds/chargebacks.
- Multi-currency.
Explain APIs, data model, core components, and how you handle consistency, idempotency, and failure modes.
Quick Answer: This question evaluates a candidate's ability in large-scale web system design, focusing on reliable payment integration, idempotency and consistency guarantees, scalability to handle traffic spikes, and operational features like receipt generation and admin analytics.