URL shortener

Turn long URLs into 7-character codes and redirect at 100× the write rate. The interesting parts are code generation without collisions and a read path that the cache, not the database, carries.

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Duration 45:00

Requirements checklist

Create a short code for a long URL, optionally with a custom alias and an expiry time.Redirect GET /{code} to the long URL with HTTP 301 or 302.Return 404 for unknown codes and 410 for expired ones.Owners can list and delete their links.Redirect latency p99 under 50 ms at the server; it sits in front of every click.Redirects 99.99% available (about 52 minutes of downtime a year); creation can tolerate brief outages.A code never maps to two different URLs, and codes are not trivially enumerable.Links are durable for at least 5 years.

Clarifying questions

How many links are created per day, and what is the read-to-write ratio?
Do we need click analytics? (It decides 301 vs 302.)
Are custom aliases allowed, and can links be edited or deleted?
Do links expire by default?
Must codes be unguessable?

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requirements

Suggested time: about 6 minutes. Also pins down 301 vs 302, enumerability, deletion semantics and durability horizon.

Notes for requirements