DoorDash System Design: Global Donations & Campaigns

You are asked to design a global donation platform that supports both ongoing giving and intense, time-bound campaigns (e.g., 3-day events). The system must let users discover causes, donate via web and mobile, and see real-time campaign progress while reliably handling surges in traffic.

Core scope: describe a high-level architecture (frontend, API gateway, stateless services, payment adapters, event pipeline, analytics, and data stores), the donation data flow (checkout → payment gateway → ledger → notification), and admin tooling for cause management and reporting. Explain how you ensure correctness of donation totals, idempotent payment handling, and integration with external charity databases and payment providers.

Interview flow / stages you should prepare for:

• Requirements clarification and prioritization (consistency vs. availability, SLAs for peak events).
• High-level architecture and component boundaries (caching, queuing, real-time updates).
• Data model and event tracking for funnel analysis and checkout flow metrics.
• Operational concerns: scalability, fault tolerance, security, and compliance (PCI/GDPR).

Skill signals to demonstrate: designing high-concurrency payment flows, idempotency and ledger consistency, real-time event streaming (leaderboards, progress bars), fraud detection, monitoring and alerting, and practical trade-offs for latency vs. consistency. Be ready to diagram APIs, sequence flows, and discuss load testing and cost considerations.