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DoorDash·Frontend Engineer·Onsite - System Design / Architecture·Intermediate

IntermediateRejected
Apr 2026

Summary

Did a system design round at DoorDash for a frontend role, which already felt off. The question was fine but the follow-up database deep-dive was brutal for someone who doesn't live in backend land. No callback, as expected.

Questions Asked (1)

Q1

Design a photo-sharing platform like Instagram, specifically accounting for how the system handles posts from accounts with massive follower counts.

System DesignData ModelingTechnical Trade-offs
Author's notes

The base question was manageable.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and scale, then focus on the frontend architecture for handling high-follower accounts. Discuss data fetching strategies, rendering optimizations, and trade-offs between consistency and performance, emphasizing how the UI adapts to massive follower counts.

Pro tip: Emphasize that for high-follower accounts, the frontend should prioritize optimistic UI updates and graceful degradation to maintain responsiveness, even if backend data is delayed. This shows you understand real-world constraints and user experience.

1. Clarify Requirements and Scale

Ask about expected user base, post frequency, and follower counts to understand the scale. Confirm whether the focus is on feed generation, post creation, or both.

2. Design Data Fetching Strategy

Propose using paginated, cursor-based APIs for feeds and posts to avoid overwhelming the client. For high-follower accounts, consider pre-fetching or caching strategies to reduce latency.

3. Optimize Rendering and State Management

Discuss virtualized lists, lazy loading, and efficient state updates to handle large volumes of posts. Use optimistic updates for likes/comments to keep UI responsive.

4. Handle Real-time Updates and Consistency

Explain how to manage real-time updates (e.g., new posts from followed accounts) without causing UI jank. Consider WebSockets or polling with backoff, and how to reconcile with local state.

5. Discuss Trade-offs and Edge Cases

Address trade-offs like consistency vs. availability, and how to handle scenarios like a celebrity posting causing a spike in feed updates. Mention fallback UIs for errors or slow networks.

Key Points to Mention

  • Cursor-based pagination for infinite scroll feeds
  • Virtualized lists (e.g., react-window) for rendering many posts
  • Optimistic UI updates for likes, comments, and follows
  • Caching strategies (e.g., service workers, CDN) for static assets and API responses
  • WebSocket or Server-Sent Events for real-time updates with throttling
  • Graceful degradation and error boundaries for network failures

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.