Design a URL shortener (e.g. bit.ly)

Classic interview: encode billions of URLs, fast redirects, optional analytics — walk through requirements to storage to scaling.

~28 minDesign interview

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Interview script (outline)

Clarify: custom aliases, expiry, analytics, private vs public links, edit/delete.
Estimate: new URLs/day, redirect QPS, read:write ratio, storage per year.
API: REST shape; 302 vs 301; idempotent create with optional idempotency key.
Encoding: counter + base62 vs random + collision check; length vs namespace.
Storage: PK, partitioning, replication for reads.
Redirect path: edge → cache → DB; cache headers.
Failure: cache miss storm, abuse, malware links.