System design interview question

Design Instagram (photo sharing + feed)

Medium · System design (HLD) · Company tags: Meta, Amazon, Microsoft, X, Snap, ByteDance, Pinterest

The prompt

"Design Instagram. Users upload photos, follow other users, and see a feed of photos from people they follow. Include the upload path and the feed path. Assume 500M daily active users."

What this round really tests

Whether the candidate treats binary media differently from metadata. Twitter is a text/fan-out problem; Instagram is a blob storage + CDN + async processing problem wearing a feed costume. A candidate who designs this exactly like Twitter has missed the point.

Clarifying questions worth asking

Photos only, or video too?
Do uploads go through our servers?
Feed ordering?
Image sizes / variants?
Stories, Reels, DMs?
Follower skew?
Do photos need to be private?

How the round usually runs

0–5 min: Scoping
5–9 min: Estimates
9–14 min: API + model
14–24 min: Architecture
24–38 min: Deep dive
38–45 min: Wrap

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