Evaluation of Web Crawler's Design

Evaluate the proposed design of the web crawler system based on the fulfillment of its non-functional requirements.

Reviewing design requirements

Let’s evaluate how our design meets the non-functional requirements of the proposed system.


Our design states that scaling our system horizontally is vital. Therefore, the proposed design incorporates the following design choices to meet the scalability requirements:

  • The system is scalable to handle the ever-increasing number of URLs. It includes all the required resources, including schedulers, web crawler workers, HTML fetchers, extractors, and blob stores, which are added/removed on demand.

  • In the case of a distributed URL frontier, the system utilizes consistent hashing to distribute the hostnames among various crawling workers, where each worker is running on a server. With this, adding or removing a crawler server isn’t a problem.

Extensibility and modularity

So far, our design is only focusing on a particular type of communication protocol: HTTP. But according to our non-functional requirements, our system’s design should facilitate the inclusion of other network communication protocols like FTP.

To achieve this extensibility, we only need to add additional modules for the newly required communication protocols in the HTML fetcher. The respective modules will then be responsible for making and maintaining the required communications with the host servers.

Along the same lines, we expect our design to extend its functionality for other MIMEA multipurpose Internet mail extension, or MIME type, is an Internet standard that describes the contents of Internet files based on their natures and formats. types as well. The modular approach for different MIME schemes facilitates this requirement. The worker will call the associated MIME’s processing module to extract the content from the document stored in the DIS.

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