Design a URL shortener at bit.ly scale

Setting

You've joined the platform team at a link-management company. Marketing customers create branded short links and need click analytics; the redirect path is on the critical path of every campaign click on the internet.

The ask

Design the system that creates short links and serves redirects, including click analytics.

Constraints & scale

• ~100M new links/month, ~10B redirects/month, heavy tail (a handful of links get 1M+ clicks/hour during launches)
• p99 redirect latency < 50 ms globally
• Links live for years; analytics must be near-real-time (< 1 min) for dashboards
• Custom aliases must be globally unique; abuse/malware links must be killable within seconds

What a strong answer covers

Requirements → estimates → API/data model → high-level diagram → 1–2 deep dives → trade-offs. Likely probes: the redirect hot path, ID generation, and analytics ingestion.

Graded on

Every session — this problem included — is scored against the same 10-dimension senior/staff rubric: