Design
News Feed Ranking System
Design the backend for a social network news feed that aggregates and ranks posts from friends/follows at massive scale.
This is a Low-Level Design (LLD) problem. New to LLD vs HLD? Start here.
01 - Why interviewers ask this
It isolates the hardest part of Instagram/Facebook — ranking at scale — and specifically tests whether you know the fan-out-on-write vs. fan-out-on-read trade-off for celebrity accounts.
02 - Where this system exists in the real world
You interact with this design every day.
Facebook/Instagram/LinkedIn feed ranking
News aggregator personalized feeds
E-commerce personalized product feeds
03 - What you'll master
Solve this once. Know it forever.
Choose fan-out strategy based on follower count
Design a candidate-retrieval-then-rank pipeline
Paginate a dynamically-ranked feed correctly
04 - What you'll design
6 functional · 3 non-functional requirements.
Aggregate posts from all accounts a user follows into one feed
5 more requirements inside
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05 - Companies that ask this
You may face this exact question in your next interview.
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