Saturday, January 28, 2012

Scaling a SaaS course to 50K+: Use the Web, Luke

Berkeley, like many schools, has departmentally-owned computer clusters so students can get temporary shell accounts for courses that have a software component or require the use of courseware.

Fine for the 108 students in CS 169 this semester.  But how can we provide over 50,000 students the necessary software infrastructure (and our in-progress textbook) to participate in the class?

Simple answer—we don’t.  The on-campus class has been relying more and more on existing commercial SaaS tools and less on Berkeley’s own IT infrastructure, in part because we thought it was important for students to use the same services and tools they’d use if they were full-time developers.  The transition is now complete:

  • We provide a VirtualBox-compatible VM image with all courseware (Ubuntu+ Ruby+ Rails+ gems+ ….) Thanks toMaggie Johnson for offering to have Google underwrite the nontrivial bandwidth charges for distributing a 1.5GB VM image to over 50,000 people via Google AppEngine.

  • More than half the students signed up at are non-USA.  The print version of our book is beyond the reach of many of these, both because of shipping and because of its $20 price (low for a textbook, high for India).  Fortunately we had always planned on doing a Kindle edition anyway, which is priced at $9.99 (for now), can be obtained instantaneously, and can be updated on demand (we’re planning a new Kindle release just before the online course begins, and probably one more before the Beta Edition comes out in Fall 2012).

  • Every student will open a free Heroku account for deploying their projects, so the autograders (and someday a Saucelabs-based grader, I hope) can check deployed code running on a public server.  Coursera apparently uses EC2 to run many instances of the autograder.

  • For code that doesn’t get deployed, we’re developing an autograder that runs rspec, reek, flay and flog, so students’ code is evaluated for both correctness and good coding style.  The feedback may not be as deep as you’d get from an experienced TA looking over your shoulder, but the approach scales way better.

  • Every student opens a Github account.  Since we need to protect homeworks against plagiarism, students need private repos for those.  The Github free account doesn’t allow that, but we’ve been working with Github to offer a free time-limited Micro account to the online students (many of whom are not traditional full-time students and so don’t qualify for Github’s free student micro plan).  Shout out to Chris Wanstrath and Kami Lott for making that happen!

Whew!  That’s the list so far.  In another post I’ll write up what we did in the textbook both to embrace the coming ebook tsunami and to make the book more interactive and connected to other online course materials, even if you get the dead-tree version.

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