Design a 3-day online donation system

Q: Design a 3-day online donation system

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.

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Question

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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.

Design a 3-day online donation system

Quick Overview

System Design: 3-day donation campaign

Requirements

Scale & reliability assumptions

Nice-to-haves (if time)

Solution

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