Design limited-time donation platform

Q: Design limited-time donation platform

This question evaluates system-design and distributed-systems competencies, covering large-scale architecture, real-time data pipelines and leaderboards, payment correctness and idempotency, storage partitioning, caching, traffic protection, observability, and failure-recovery planning.

Q: How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

Q: What difficulty level is this interview question?

This is a hard difficulty System Design question, commonly asked during Technical Screen rounds at DoorDash.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at DoorDash during technical interviews.

Question

System Design: Donations Platform for a Three-Day Global Fundraising Campaign

Context

You are to design an internet-scale donations platform for a time-bounded, three-day global fundraising campaign. The platform must handle significant traffic spikes during live events, provide real-time visibility into totals and leaderboards, ensure payment correctness, and remain highly available across regions.

Requirements

Design and specify the following:

Functional APIs
- Create donation (intent), confirm payment, refund.
- Query: totals and leaderboards (by campaign, country, team, etc.).
Data model
- Core entities (campaign, donation, payment, refund, donor/PII segregation, ledger), indexes, and unique constraints.
Idempotency and deduplication
- Strategy for client retries and provider webhook retries; prevention of double-submits.
Real-time totals and leaderboards
- Running totals with sub-second updates; unique donors, top teams/countries.
Risk controls
- Fraud checks and deduplication heuristics; velocity limits.
Traffic protection
- Rate limiting, backpressure, and load shedding.
Webhooks
- Handling delayed/out-of-order/duplicated payment provider webhooks and reconciliation.
Scalability and availability
- Design for global traffic spikes; multi-region availability; explicit consistency trade-offs.
Storage and partitioning
- OLTP vs. streaming/warehouse; partitioning, replication, and hot campaign handling.
Caching
- Strategy for campaign config, totals, and leaderboards.
Streaming and analytics
- Near-real-time pipelines for metrics and BI.
Observability
- Metrics, logs, traces, dashboards, and alerting.
Failure scenarios
- Payment provider outage, double-submits, partial failures; recovery and user experience.
Capacity estimates
- Back-of-the-envelope RPS/QPS, storage, throughput; latency budgets.
Rollout and testing
- Phased rollout, load tests, chaos/failure drills, and monitoring gates.

Design limited-time donation platform

Quick Overview

System Design: Donations Platform for a Three-Day Global Fundraising Campaign

Context

Requirements

Solution

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