scraping-workflow-summary.md

Scraping flow

Summary

Before we head deeper into the features, let's recap on how Crawlee scrapers work. In short:

---
title: Basic web scraping flow
---
flowchart TB
  URL -- turned into --> Request -- URL loaded --> Webpage --> data[Extracted data]
  Webpage -- Add URLs to scrape --> URL

In-depth

1. You define a list of URLs to be scraped, and configure the scraper.

2. You then start a scraper Run. Your URLs are turned into Requests, and put into the RequestQueue.

3. A single Run may start, in parallel, several scraper Instances.

4. Each Instance takes a Request from RequestQueue, and loads the URL. Based on the URL loaded:

   • The data is scraped from the page and sent to the Dataset.
   • New URLs are found, turned into Requests, and sent to RequestQueue.

5. Step 4. continues for as long as there are Requests in RequestQueue.

6. In CrawleeOne, the Instance processes Requests in Batches. Requests in a single Batch share the same state and browser instance.

---
title: Scraper run
---
flowchart TB
  URLs --> reqq[RequestQueue]
  reqq --> run[Scraper run]

  run --> instance
  run --> instance
  run --> instance

  subgraph instance[Scraper instance]
    instance_note["Single run may include several instances.<br/>Each instance has separate state."]
  end

  subgraph batch[Batch of Requests]
    batch_note[Each instance processes a batch of URLs.<br/> Then it restarts it's state.]
  end

  instance --> batch

  batch --> urlflow
  batch --> urlflow
  batch --> urlflow

  subgraph urlflow[For each URL]
    direction TB
    URL -- turned into --> Request -- URL loaded --> Webpage --> data[Extracted data]
    Webpage -- Add URLs to scrape<br/>to RequestQueue --> URL
  end