System Design: Web Crawler

Introduction

A web crawler is an internet bot that systematically scoursTo go or move swiftly about, over, or through in search of something. the World Wide Web (WWW) for content, starting its operation from a pool of seed URLs. This process of acquiring content from the WWW is called the crawling process. The crawler further saves the content in data stores, ensuring the data is available for later use. Efficient storage and subsequent retrieval of this data are integral to designing a robust system.

The core functionality of a web crawler involves fetching web pages, parsing their content and metadata, and extracting new URLs or lists of URLs for further crawling. This is the first step performed by search engines. The output of the crawling process serves as input for subsequent stages such as:

• Data cleaning

• Indexing

• Relevance scoring using algorithms like PageRank

• URL frontier management

• Analytics

This specific design problem is focused on web crawlers’ System Design and excludes explanations of the later stages of indexing, ranking in search engines, etc. To learn about some of these subsequent stages, refer to our chapter on distributed search.