DoorDash·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say

Jul 2026

Summary

System design round at DoorDash for a software engineer role. The question was a full end-to-end design of a news-feed feature, the kind where you think you know where to start and then realize thirty minutes in you've barely scratched the surface.

Questions Asked (1)

Design a news-feed feature for a food discovery app. The feed shows titles, authors, summaries, and engagement counts. Tapping an item opens a detail view with the full post, comments, and related items. Cover data modeling, APIs, ranking, request paths, fan-out, caching, search, scalability, consistency, and error handling end to end.

System DesignData ModelingTechnical Trade-offs

Author's notes

This is a monster of a question.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and scale, then design a high-level architecture covering data models, APIs, and feed generation. Dive into trade-offs for ranking, fan-out, caching, and consistency, and wrap up with error handling and scalability considerations.

Pro tip: Emphasize how you would handle the 'celebrity problem' (users with many followers) by using a hybrid fan-out approach, and discuss how to ensure feed consistency while maintaining low latency.

1. Clarify Requirements and Scale

Ask questions to understand functional and non-functional requirements, such as expected DAU, read/write ratio, latency targets, and consistency needs.

2. Design Data Models and APIs

Define schemas for posts, users, comments, and engagement metrics, and outline RESTful or GraphQL APIs for feed retrieval and post details.

3. Architect Feed Generation and Ranking

Choose between push (fan-out on write) and pull (fan-out on read) models, and describe a ranking algorithm that balances recency, engagement, and personalization.

4. Address Scalability, Caching, and Consistency

Explain how to scale with sharding, caching strategies (e.g., Redis for hot feeds), and trade-offs between strong and eventual consistency.

5. Cover Search, Error Handling, and Edge Cases

Discuss search integration (e.g., Elasticsearch), error handling for API failures, and edge cases like deleted posts or inactive users.

Key Points to Mention

Hybrid fan-out approach to handle both normal users and celebrities efficiently.
Use of caching layers (e.g., Redis) to store precomputed feeds for fast reads.
Ranking algorithm that incorporates engagement counts, recency, and user preferences.
API design with pagination and cursor-based navigation for scalability.
Trade-offs between consistency and availability (e.g., eventual consistency for feeds).
Error handling strategies such as retries, circuit breakers, and fallback to stale data.

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