System design interview questionHardSocial / Feed
Design a News Feed like Twitter or Facebook
Design Twitter/Facebook-style news feed: users post, followers see a personalized timeline quickly.
Interview scope
Client → Gateway/LB → App → Cache + DB; Message Queue for fan-out/async. No Client → DB/Cache.
Functional requirements
- Create a post.
- Read a home/timeline feed for a user.
- Handle follow relationships at a high level.
Scale and quality goals
- Feed reads must be fast (cache-friendly).
- Publishing to many followers should use async fan-out where needed.
- Don’t rebuild the whole feed from raw posts on every scroll with no cache.
Capacity assumption
Design for this scale
Assume ~100M DAU, ~2 posts/user/day, feed reads >> writes. Celebrity fan-out is the hard part.
Practice more than a diagram
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