QA
Intermediate LevelSystem Design & Architecture

How do you design a Distributed Web Crawler (like Google Bot)?

❓ Interview Prompt: Explain designing a Web Crawler, URL Frontier, politeness delay queues, HTML fetchers, Bloom Filters, and deduplication.

Designing a high-throughput Distributed Web Crawler (Google Bot):

Architecture:

1
URL Frontier: Prioritized crawling queue enforcing domain politeness delays (e.g. max 1 request per second per host IP).
2
HTML Fetchers: Asynchronous HTTP workers executing page fetches.
3
URL Deduplication: Uses a Bloom Filter to verify if a discovered URL has already been crawled before enqueueing.
4
Document Deduplication: Computes SimHash distance to detect duplicate content across different URLs.

Code Implementation Example

markdown
Distributed Web Crawler Architecture:

[URL Seed List] ──> [URL Frontier Queue] ──> [HTML Fetcher Pool]
                         ▲                         │
                         │                   (Extract Links)
                 (Unvisited URLs)                  │
                         │                         ▼
                  [Bloom Filter] <─── (Check URL Duplicate)
💡Distributed Web Crawler architecture with URL Frontier and Bloom Filter deduplication.
🎯 Interview Key Takeaway

Design web crawlers using a URL Frontier for domain politeness and Bloom Filters for URL deduplication.

#System Design#Web Crawler#Bloom Filter#URL Frontier#Intermediate
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