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Instagram System Design
Visual Problem Diagram
Scenario
A influencer's Reel hits 2M views in an hour—image bytes must come from the nearest edge, likes must not double-count on retry, and the home feed still needs to feel fresh without ranking every post on every scroll. The interview blends media pipeline, feed fan-out, and social graph—not filters as the main event.
Design a photo-sharing social network where users upload images and videos, follow others, and scroll a personalized feed with likes and comments. Mobile upload reliability and CDN-backed media delivery dominate ops; feed assembly reuses fan-out/hybrid patterns from large-scale social timelines.
You should support media upload, feed, profiles, likes/comments, and optional ephemeral stories. Be ready to walk through upload + transcoding, feed read path, celebrity scale, and counter consistency on viral posts.
Constraints
Upload photos/video, follow graph, home feed, likes/comments, profiles, optional stories
< 300 ms feed p95, 99.9% availability, durable media, eventual engagement counts acceptable briefly
1B+ users, 500M DAU, hundreds of millions of posts/day, viral posts to millions of likes, heavy CDN egress
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