URL Shortener — Simple

Problem statement (interviewer prompt)

Design a service like bit.ly: shorten a long URL into a 6–8 character code, redirect on access, and report basic click analytics. Support custom aliases, expiry, and 100M new URLs/day with 100:1 read:write — at <100ms redirect latency.

flowchart LR
  U([User])
  W([Web / API])
  ID([ID Generator])
  KV[(Key-Value Store<br/>short -> long)]
  C[(Cache)]
  U -->|POST /shorten| W
  W --> ID
  W --> KV
  U -->|GET /:code| W
  W --> C
  C -. miss .-> KV
  W -- 301/302 --> 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,W client;
    class KV,C datastore;
    class ID compute;