Ever wondered how google.com works? What's under the hood that enables any user to insert a string and obtain related results from the web, given it's inherent complexity and vastity? How does the search engine indexes all those websites and relate their contents with the input string?

We'll try to answer some of these questions by building a simplified version of the main component that power every search engine at his simplest: a web crawler. We won't cover all sofistications and ranking algorithms at the core of the google engine, they're the result of years of research and improvements and it would require a book on its own just to scratch the surface on those topics.

This will be a tutorial on how to build something akin to a raw search engine starting from its inner-most component and extending it by adding features chapter by chapter.
The repository containing the code is https://github.com/codepr/webcrawler. During the journey we'll touch many system design concepts:

• Microservices
• Middlewares
• Network unreliability
• Concurrency
• Scalability
  • Consistency patterns
  • Availability patterns

And more in depth on the topic:

• Web crawler main characteristics
  • Politeness
  • Crawling rules
• Reverse indexing services
• Content signatures