URL shortener

A URL shortener maps short keys to long URLs with fast redirects, low latency reads, and collision-safe key generation. Core components: API for create/redirect, key generation (base62 counter or hash), relational or KV store for mappings, cache for hot links, and analytics pipeline optional.

Redirects are read-heavy — cache popular keys at CDN or Redis. Custom aliases need uniqueness checks. Plan abuse detection and rate limits on creation. Estimate billions of keys — 7-char base62 scales far.

On interviews: sketch create and redirect APIs, key generation strategy, storage schema, and caching for viral links.

Common pitfalls: sequential IDs enumerable by attackers; no cache on redirect path; analytics slowing redirect hot path.

The trade-off is flexibility versus complexity—know when the simpler path is enough.

Checklist:

• Design create and redirect flows.
• Choose key generation and collision handling.
• Cache hot mappings at edge or Redis.
• Add rate limits and abuse controls.