OpenTracker

This is an ode to Dirk Engling’s OpenTracker.

It’s a BitTorrent tracker.

It’s what powered The Pirate Bay in 2007–2009.

I’ve been using it to power the downloads on http://driverpacks.net since the end of November 2010. >6 years. It facilitated 9839566 downloads since December 1, 2010 until today. That’s almost 10 million downloads!

Stability

It’s one of the most stable pieces of software I ever encountered. I compiled it in 2010, it never once crashed. I’ve seen uptimes of hundreds of days.

wim@ajax:~$ ls -al /data/opentrackertotal 456drwxr-xr-x  3 wim  wim   4096 Feb 11 01:02 .drwxr-x--x 10 root wim   4096 Mar  8  2012 ..-rwxr-xr-x  1 wim  wim  84824 Nov 29  2010 opentracker-rw-r--r--  1 wim  wim   3538 Nov 29  2010 opentracker.confdrwxr-xr-x  4 wim  wim   4096 Nov 19  2010 src-rw-r--r--  1 wim  wim 243611 Nov 19  2010 src.tgz-rwxrwxrwx  1 wim  wim  14022 Dec 24  2012 whitelist

Simplicity

The simplicity is fantastic. Getting up and running is incredibly simple: git clone git://erdgeist.org/opentracker .; make; ./opentracker and you’re up and running. Let me quote a bit from its homepage, to show that it goes the extra mile to make users successful:

opentracker can be run by just typing ./opentracker. This will make opentracker bind to 0.0.0.0:6969 and happily serve all torrents presented to it. If ran as root, opentracker will immediately chroot to . and drop all priviliges after binding to whatever tcp or udp ports it is requested.

Emphasis mine. And I can’t emphasize my emphasis enough.

Performance & efficiency

All the while handling dozens of requests per second, opentracker causes less load than background processes of the OS. Let me again quote a bit from its homepage:

opentracker can easily serve multiple thousands of requests on a standard plastic WLAN-router, limited only by your kernels capabilities ;)

That’s also what the homepage said in 2010. It’s one of the reasons why I dared to give it a try. I didn’t test it on a “plastic WLAN-router”, but everything I’ve seen confirms it.

Flexibility

Its defaults are sane, but what if you want to have a whitelist?

  1. Uncomment the #FEATURES+=-DWANT_ACCESSLIST_WHITE line in the Makefile.
  2. Recompile.
  3. Create a file called whitelist, with one torrent hash per line.

Have a need to update this whitelist, for example a new release of your software to distribute? Of course you don’t want to reboot your opentracker instance and lose all current state. It’s got you covered:

  1. Append a line to whitelist.
  2. Send the SIGHUP UNIX signal to make opentracker reload its whitelist1.

Deployment

I’ve been in the process of moving off of my current (super reliable, but also expensive) hosting. There are plenty of specialized companies offering HTTP hosting2 and even rsync hosting3. Thanks to their standardization and consequent scale, they can offer very low prices.

But I also needed to continue to run my own BitTorrent tracker. There are no companies that offer that. I don’t want to rely on another tracker, because I want there to be zero affiliation with illegal files4. This is a BitTorrent tracker that does not allow anything to be shared: it only allows the software releases made by http://driverpacks.net to be downloaded.

So, I found the cheapest VPS I could find, with the least amount of resources. For USD $13.505, I got the lowest specced VPS from a reliable-looking provider: with 128 MB RAM. Then I set it up:

  1. ssh‘d onto it.
  2. rsync‘d over the files from my current server (alternatively: git clone and make)
  3. added @reboot /data/opentracker/opentracker -f /data/opentracker/opentracker.conf to my crontab.
  4. removed the CNAME record for tracker.driverpacks.net, and instead made it an A record pointing to my new VPS.
  5. watched http://tracker.driverpacks.net:6969/stats?mode=tpbs&format=txt on both the new and the old server, to verify traffic was moving over to my new cheap opentracker VPS as the DNS changes propagated

Drupal module

Since driverpacks.net runs on Drupal, there of course is an OpenTracker Drupal module to integrate the two (I wrote it). It provides an API to:

  • create .torrent files for certain files uploaded to Drupal
  • append to the OpenTracker whitelist file6
  • parse the statistics provided by the OpenTracker instance

You can see the live stats at http://driverpacks.net/stats.

Conclusion

opentracker is the sort of simple, elegant software design that makes it a pleasure to use. And considering the low commit frequency over the past decade, with many of those commits being nitpick fixes, it also seems its simplicity also leads to excellent maintainability. It involves the HTTP and BitTorrent protocols, yet only relies on a single I/O library, and its source code is very readable. Not only that, but it’s also highly scalable.

It’s the sort of software many of us aspire to write.

Finally, its license. A glorious license indeed!

The beerware license is very open, close to public domain, but insists on honoring the original author by just not claiming that the code is yours. Instead assume that someone writing Open Source Software in the domain you’re obviously interested in would be a nice match for having a beer with.

So, just keep the name and contact details intact and if you ever meet the author in person, just have an appropriate brand of sparkling beverage choice together. The conversation will be worth the time for both of you.

Dirk, if you read this: I’d love to buy you sparkling beverages some time :)

  1. kill -s HUP <code>pidof opentracker ↩︎

  2. I’m using Gandi’s Simple Hosting. ↩︎

  3. https://rsync.net ↩︎

  4. Also: all my existing torrents use http://tracker.driverpacks.net:6969/announce as the URL. The free trackers I could find were all using udp://. So new leechers would then no longer be able to find the hundreds of existing seeders. Adding trackers to already-downloaded torrents is not possible. ↩︎

  5. $16.34 including 21% Belgian VAT. ↩︎

  6. Rather than having the Drupal module send a SIGHUP from within PHP, which requires elevated rights, I instead opted for a cronjob that runs every 10 minutes: */10 * * * * kill -s HUP <code>pidof opentracker. ↩︎

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