Mock Interview Prompt 004: News Feed

Prompt

Design a social media news feed similar to Facebook or Instagram home feed.

Interviewer Notes

Candidates should explore:

• fan-out on write vs fan-out on read
• ranking vs chronological feed
• follower graph scale
• celebrity problem
• cache invalidation and freshness

Optional Follow-Ups

• Support stories or ephemeral posts
• Personalized ranking
• Ad insertion
• Multi-region feed serving
• Feed generation under celebrity load

What Strong Answers Usually Cover

• post creation pipeline
• social graph considerations
• feed generation strategy
• cache design and invalidation
• hot user handling
• trade-offs between latency, freshness, and cost