Instagram — Simple

Problem statement (interviewer prompt)

Design Instagram: photo + video upload with multiple resolutions, a personalised feed, stories (24h TTL), reels, hashtag and user search, likes/comments/saves, and direct messaging. Handle 100M photo uploads/day and 2B MAU.

flowchart LR
  U([User])
  UP[Upload Service]
  T([Transcode])
  S3[(Object Store)]
  CDN[CDN]
  META[(Metadata DB)]
  FEED[Feed API]
  FAN[[Fan-out]]
  TL[(Timelines)]
  U -->|post photo| UP --> T --> S3 --> CDN
  UP --> META --> FAN --> TL
  U -->|feed| FEED --> TL
  FEED --> META
  CDN --> U

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class U client;
    class CDN edge;
    class UP,FEED service;
    class META,TL datastore;
    class FAN queue;
    class T compute;
    class S3 storage;