Design a URL shortener (like bit.ly).
Answer
- Requirements: shorten, redirect, optional custom alias and expiry; read-heavy (e.g. 100 reads per write).
- API:
POST /urls {long_url} → short code; GET /{code} → 301/302 redirect (302 if you want click analytics). - Code generation: base62 of a unique ID (DB sequence or Snowflake-style IDs); 7 characters ≈ 3.5 trillion codes. Or hash + collision check.
- Storage: key-value table
code → long_url, created_at, expires_at. - Cache popular codes in Redis; redirects at the edge/CDN.
- Analytics as async events to a queue.
- Abuse: rate limits, malicious URL scanning.
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