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Design a large-scale web crawler that fetches billions of pages while being polite and avoiding traps.

Crawling a few pages is trivial. Crawling the web means a URL frontier with priority, politeness per host, dedup at billions of URLs, and defenses against spider traps and infinite content. Here is the crawler architecture that scales without getting your IPs banned.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.

Crawling a few pages is trivial. Crawling the web means a URL frontier with priority, politeness per host, dedup at billions of URLs, and defenses against spider traps and infinite content. Here is the crawler architecture that scales without getting your IPs banned.

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Applied AI Engineering·The interviewPremium14mDriving the design conversationA design round is a conversation you are expected to lead, not a question you answer. This lesson is the shape that works, the four moments that decide the outcome, and the two classic ways strong candidates lose one.Applied AI Engineering·The interviewPremium12mTurning this course into a study planA concrete four-week plan mapping the seven modules onto the question bank, plus what to do differently if your interview is next week rather than next month.
UP NEXT ON YOUR JOURNEY
Next in this trackDesign a real-time leaderboard that ranks millions of players and updates scores instantly.Next in this trackDesign a geo-proximity service that finds the nearest places to a user, like Yelp or store locators.Next in this trackDesign an idempotent job queue that processes background tasks exactly once despite retries and crashes.
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