Design a food news feed and backend flow

Q: Design a food news feed and backend flow

This question evaluates skills in scalable system design, data modeling, API design, and end-to-end backend data flow for high-throughput social feeds, categorized under System Design and emphasizing practical application of distributed architectures alongside conceptual trade-offs.

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 Onsite 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

Context

You are building a social, news-feed-like feature inside a food discovery or delivery app. Users follow authors (people, creators, or restaurants). The home feed shows a list of recent and relevant food posts. Tapping a post opens a detail modal with the full post content and comments.

Requirements

UI behavior
- Feed items show: title, author, and comment count.
- Selecting a feed item opens a detail modal with full post information and a paginated comments list.
Deliverables
- Data model for users, follows, posts, comments, feed, and counters.
- APIs for: list feed, fetch post detail, and post comment. Include pagination and idempotency where relevant.
- Pagination and ranking strategy for the feed.
- End-to-end backend request flow after the API gateway, including services, message queues, databases, and caches.
- How a new post is processed and propagated to follower feeds (fan-out vs fan-in).
- Discussion of consistency, caching, indexing, rate limiting, and optimizations for latency and read/write throughput.

Assumptions (clarify during interview if needed)

Users see a personalized home feed from authors they follow, with light ranking over recency.
Scale target: millions of DAU, thousands of posts per second at peak, tens of thousands of comments per minute.
Mobile clients; images and videos are stored in object storage and served via CDN.

Design a food news feed and backend flow

Quick Overview

Context

Requirements

Assumptions (clarify during interview if needed)

Solution

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Design a food news feed and backend flow

Quick Overview