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Problem Understanding
Restate the problem in your own words.
Design Instagram (Photo feed)
Design Instagram-class photo + short-video sharing: a feed of posts, profiles, the follow graph, search by hashtag and user, comments, and a recommender. Reads dominate — the feed is hit on every app launch by 2B+ users — and the photo path is latency-sensitive, served from a CDN. The hard parts are the feed mix (chronological + recommender), the upload pipeline (multi-bitrate encode for video), and the long-tailed media storage at petabyte scale.
- Instagram~2B MAU, photo-first with reels/video. Feed is a recommender mix; stories are a separate ephemeral surface.
- PinterestVisual discovery feed with a heavy recommender; same media pipeline + cache strategy.
- SnapchatPhotos and short videos with a stronger ephemeral default — storage TTL is the headline difference.
- TikTokVideo-only feed where the recommender does almost all the work — follow graph is secondary.
Your task: read the problem above, then write what the system is, who uses it, the rough scale, and the headline UX expectation — in your own words. Submit for AI review when you're ready.
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