Design a Large-Scale Polite Web Crawler
Last updated: August 6, 2026
Quick Overview
Design a large-scale polite web crawler that efficiently gathers data from the web while respecting the rules set by websites.
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Design a large-scale polite web crawler that efficiently gathers data from the web while respecting the rules set by websites.
This question is often asked during onsite interviews for software engineering roles at Google to assess a candidate's ability to design scalable systems. The interviewer evaluates the candidate's understanding of web protocols, data management, and system architecture, as well as their ability to balance efficiency with ethical considerations in web crawling.
What the Interviewer Expects
- Explain the requirements and constraints of the web crawler.
- Design a high-level architecture including components like the scheduler, downloader, and storage.
- Discuss how to implement politeness policies such as respecting robots.txt and rate limiting.
- Identify potential scaling issues and propose solutions.
- Consider data storage and retrieval strategies for large volumes of data.
Key Topics to Cover
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- How would you handle duplicate content in your crawler?
- What strategies would you use to ensure your crawler is efficient?
- How would you implement fault tolerance in your design?
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Practice System Design ProblemsSample Answer
Requirements
To design a large-scale polite web crawler, we first need to define the requirements. The crawler should gather data from various websites while adhering to the rules specified in the robots.txt file....
High-Level Design
The architecture of the web crawler can be broken down into several key components:
- Scheduler: Manages the queue of URLs to crawl, prioritizing based on factors like freshness and importance. ...
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