Design a 3-day donation campaign platform
Overview
This question evaluates system design competencies such as scalable distributed architecture, payment integration and financial correctness, real-time analytics and leaderboards, traffic spike handling, and observability for a time-bounded fundraising campaign.
DoorDash
Aug 7, 2025, 12:00 AM
Software Engineer
Technical Screen
System Design
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System Design: 3-Day High-Traffic Donations Platform
Context
Design a donations platform to support a time-bounded, high-traffic fundraising campaign that runs for exactly three days. The platform must accept payments reliably at large, spiky volumes; display real-time progress and leaderboards; and cleanly start/stop at the scheduled times. Assume web and mobile clients.
What to Deliver
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Functional requirements
- Donation flow (intent, authorization/capture, receipts), refunds/chargebacks
- Matching gifts and caps, leaderboards and real-time counters
- Scheduled start/end behavior and gating
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Non-functional requirements
- Throughput targets, availability/SLOs, latency, cost considerations
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System components and architecture
- API gateway, payment processor integration
- Idempotency and retries, fraud detection, rate limiting
- Data model, analytics/events, real-time counters
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Cross-cutting concerns
- Handling traffic spikes, multi-region readiness
- Storage choices; consistency vs durability trade-offs
- Observability and auditing
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Rollout plan
- Load testing strategy, canary/feature-flag rollout, game-day readiness
Keep the design pragmatic for a three-day event while ensuring financial correctness and user trust.
Solution
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