Art of Codeartofcode
Lesson 11 of 15

31. Design a URL Shortener

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The interview prompt
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31.1 What do you ask first?
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31.2 How big is this, really?
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31.3 What are the doors?
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31.4 What do we store?
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31.5 What does the whole system look like?
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31.6 How do you generate the short code?
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31.7 301 or 302?
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31.8 How do you keep redirects fast at 12,000 a second?
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31.9 How do you count clicks without slowing redirects?
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31.10 What would you say in the last five minutes?
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Score yourself
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Variations to practise
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Sources
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Code lab
31. Design a URL Shortener

31.10 What would you say in the last five minutes?

3 min read+10 XP

Step 6: Wrap-up (5 minutes)

A strong close names the weak spots before the interviewer does:

  • Bottleneck: the read path. Covered by Redis, replicas and an in-process cache for viral links.
  • Single points of failure: the ticket server (blocks buffer it; run it redundantly), the primary database (failover to a replica).
  • Abuse: rate-limit link creation per client (Chapter 25), and check new URLs against a malware list before saving them.
  • Next with more time: link expiry with a cleanup job, custom aliases (a uniqueness check on the alias), and a second region for disaster recovery (Chapter 29).

Memory code: "Name the weak spots before they do."