Design a scalable news feed system
Overview
This System Design question evaluates a candidate's ability to design scalable backend systems for a social app news feed, covering data modeling, API design, real-time updates, ranking, privacy controls, and operational concerns such as sharding, caching, and monitoring.
Lyft
Jul 27, 2025, 12:00 AM
Software Engineer
Onsite
System Design
0
0
Design the backend for a social app news feed
Context
You are designing the backend that powers a mobile social app's home/news feed at large scale. The system must handle high write throughput (users publishing posts) and high read throughput (users opening and scrolling feeds), while supporting real-time updates, ranking, and privacy.
Tasks
- Define functional and non-functional requirements.
- Propose a data model for posts, users, relationships, and feeds.
- Specify core APIs: publish, follow/unfollow, getFeed (include pagination), and real-time update approach.
- Compare fan-out-on-write vs. fan-out-on-read. Choose an approach under high write and read loads and justify.
- Cover the following: ranking, real-time updates, deduplication, privacy/blocks, backfilling after new follows, cold-start for new users, caching, storage and indexing, sharding and partitions, consistency and ordering guarantees, failure handling, and monitoring.
- Provide capacity estimates with clearly stated assumptions.
- Present a high-level architecture diagram description (components and data flow).
Solution
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