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We had a "Web Crawler Developer" MeetUp at this year's ApacheCon US in Oakland.

It wound up being an UnMeetUp (MeetDown?) on Wednesday, November 4th from 11am - 1pm.


  • Andrzej Bialecki - Apache Nutch
  • Thorsten Sherler - Apache Droids
  • Michael Stack - Formerly with Heritrix, now HBase
  • Ken Krugler - Bixo



  • Nutch - become more component based.
  • Droids - get more people involved.

Sharable Components

  • robots.txt parsing
  • URL normalization
  • URL filtering
  • Page cleansing
    • General purpose
    • Specialized
  • Sub-page parsing (portlets)
  • AJAX-ish page interactions
  • Document parsing (via Tika)
  • HttpClient (configuration)
  • Text similarity
  • Mime/charset/language detection


  • Needs help to become really usable
  • Would benefit from large test corpus
  • Could do comparison with Nutch parser
  • Needs option for direct DOM querying (screen scraping tasks)
  • Handles mime & charset detection now (some issues)
  • Could be extended to include language detection (wrap other impl)

URL Normalization

  • Includes both domain ( ==, path, and query portions of URL
  • Often site-specific rules
    • Option to derive rules using URLs to similar documents.

AJAX-ish Page Interaction

  • Not applicable for broad/general crawling
  • Can be very important for specific web sites
  • Use Selenium or headless Mozilla

Component API Issues

  • Want to avoid using an API that's tied too closely to any implementation.
  • One option is to have simple (e.g. URL param) API that takes meta-data.
    • Similar to Tika passing in of meta-data.

Hosting Options

  • As part of Nutch - but easy to get lost in Nutch codebase, and can be associated too closely with Nutch.
  • As part of Droids - but Droids is both a framework (queue-based) and set of components.
  • New sub-project under Lucene TLP - but overhead to set up/maintain, and then confusion between it and Droids.
  • Google code - seems like a good short-term solution, to judge level of interest and help shake out issues.

Next Steps

  • Get input from Gordon re Heritrix. Stack to follow up with him. Ideally he'd add his comments to this page.
  • Get input from Thorsten on Google code option. If OK as starting point, then Andrzej to set up.
  • Make decision about build system (and then move on to code formatting debate (big grin)
    • I'm going to propose ant + maven ant tasks for dependency management. I'm using this with Bixo, and so far it's been pretty good.
  • Start contributing code
    • Ken will put in robots.txt parser.

Original Discussion Topic List

Below are some potential topics for discussion - feel free to add/comment.

  • Potential synergies between crawler projects - e.g. sharing robots.txt processing code.
  • How to avoid end-user abuse - webmasters sometimes block crawlers because users configure it to be impolite.
  • Politeness vs. efficiency - various options for how to be considered polite, while still crawling quickly.
  • robots.txt processing - current problems with existing implementations
  • Avoiding crawler traps - link farms, honeypots, etc.
  • Parsing content - home grown, Neko/TagSoup, Tika, screen scraping
  • Search infrastructure - options for serving up crawl results (Nutch, Solr, Katta, others?)
  • Testing challenges - is it possible to unit test a crawler?
  • Fuzzy classification - mime-type, charset, language.
  • The future of Nutch, Droids, Heritrix, Bixo, etc.
  • Optimizing for types of crawling - intranet, focused, whole web.
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