Design a high-scale URL shortener

Q: Design a high-scale URL shortener

This is a System Design interview question from Microsoft for Software Engineer roles. View the full question and solution on PracHub.

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Question

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Design a URL shortening service.

Core APIs / Features

Create short URL : accept a long URL and return a short code / short URL.
Redirect : given a short code, redirect to the original long URL.
Optional:
- Expiry (TTL) for short links
- Analytics (click counts, time series, referrer, geo/device, etc.)
- Admin / management (list links, disable/delete, etc.)

Scale assumptions

~ 1M creates/day
~ 1B redirects/day (read-heavy)

Follow-up requirements

Multi-region / global low latency : how do you serve redirects quickly worldwide (geo routing, load balancing, caching strategy, consistency trade-offs)?
Write spike durability : if create traffic spikes from ~300–500 QPS to 1000 QPS , how do you guarantee every create request is processed without dropping (e.g., queue/worker, retries, DLQ, idempotency, backpressure)?

Design a high-scale URL shortener

Core APIs / Features

Scale assumptions

Follow-up requirements

Solution

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