YouTube — Simple

Problem statement (interviewer prompt)

Design YouTube: resumable video upload from creators, multi-resolution + multi-codec transcoding, global CDN delivery with adaptive bitrate, recommendation-driven discovery, comments, live streaming, and copyright (Content ID). Handle 500h of video uploaded per minute.

flowchart LR
  U([Creator])
  UP[Upload Service]
  S3[(Origin Storage)]
  TR([Transcoder])
  CDN
  META[(Metadata DB)]
  V([Viewer])
  REC([Recommendations])
  U --> UP --> S3 --> TR --> CDN
  UP --> META
  V --> CDN
  V --> REC
  REC --> META

    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,V client;
    class UP service;
    class META datastore;
    class TR,REC compute;
    class S3 storage;