gpollice

A Case for Virtualization

In Computer science, OpenSource, Software Engineering, Tools on December 7, 2011 at 9:56 am

Maybe I’m late to the party, but until recently I had not paid much attention to using virtual machines on a regular basis. I figured that since I had a couple of desktop Windows systems and a couple of Mac notebooks, I’d be able to use almost any software I wanted without any problems. Well, that’s probably true, but when you begin to use lots of different software tools, especially open source tools that have many dependencies, things begin to get really sticky. And, when you try to figure out how to put together the software needed for students in your courses…well, let’s just say that if I had any hair left on my head, it would be gone. I am convinced that dependencies are the hobgoblins of open source.

If you’ve read some of my more recent posts, I’ve been playing with Cucumber for use in my upcoming Testing for Developers course. I want the students to be exposed to lots of tools and that means that we have a need for lots of different languages, especially some of the dynamic languages, on the system. While Microsoft makes developing software for Windows relatively easy, it’s not my favorite platform for doing anything outside of the Microsoft ecosystem. I understand that and I’m not complaining. In the words of Bill Belichick, “it is what it is.” So, I do almost all of my development on my Macbook. It’s fast and it’s pretty much Linux (the key words here are pretty much).

If you stick to just Java, C, or C++ it turns out that almost any platform works as well as the other. I mean, if you load MinGW onto a Windows system you have the ability to develop from the C family. Add Eclipse and you’ve got a pretty portable IDE. But, when you start to look out from these languages, things get really murky.

A Concrete Example

Let’s look at a real example of what I’m getting at, setting up Cucumber for the class. We’ll start by just considering my Mac setup. Cucumber is written in Ruby and works really well if you have simple scenarios that you use to exercise some simple Ruby code. By simple Ruby code I mean code that has no GUI, database, Internet, or other features. In other words, code that’s probably not very useful for a real application.

As I went through the examples in The Cucumber Book, I began to need additional components like Sinatra, Capybara, and a many others that I have no experience with. Well, how do you get all of this to work? Do they all really work together seamlessly? Maybe, if you have the right versions and the right versions of Ruby and other gems that you have.

It turns out that I had four versions of Ruby on my system. I had ruby 1.8.7, 1.9.1, 1.9.2, and MacRuby. What’s worse is that I didn’t realize it. Some of them were installed in a standard location (whatever that means). If I reordered the sequence of directories in my PATH, I got a different version of Ruby. I needed some consistency. I was using Ruby 1.9.1 and things were going along fairly well when I needed to get the service_manager gem. I installed is using the standard “gem install” approach. Then, when I tried to use it, there was a problem with readline.

After several hours of searching the Web, tweeting to a few friends, posting on stackoverflow, and The Cucumber Book forum, I got an answer that let me get past this. But things had deteriorated to the point that I had no idea what was installed, where. I had used bundler for some things, gem for others, and done some downloading packages, source code that I built, and other ways of getting the software on my system. I also tried rvm, but frankly by this time I wasn’t sure what I was doing and the documentation wasn’t very helpful. Do you need to be using bash? How do you get it working with other shells? I was sitting on a software stack that was about to come crashing down. I could feel it in my bones.

Rewind

I decided to remove everything Ruby on my system and start over. Okay, that was another few hours, making sure that I copied everything I removed just in case I really messed it up. I finally was ready to start over. Thanks to Matt Wynne, one of the authors of The Cucumber  Book, I ended up using rvm, the Gemfile from the latest version of the installation appendix in the book, and I got the right version of Ruby installed along with the gems and packages I needed. Now, this wasn’t perfect, but it was manageable. Some of the documentation was a little bit off and I had to get on the rvm IRC channel to ask for help, but I did it.

Enter the Virtual Machine

Well, this was great. I now had a consistent installation on my Mac. Most of my students don’t use Mac. Some use Windows, some use Linux. Since they’re computer science students—advanced undergraduates and graduate students—I’m safe assuming that they know their way around Linux. If I could get the software configured on a Linux virtual machine, I could just give the students the VM image. Then I could either add new software for other topics I expect to cover in the course or simply create a different VM image.

I’ve been using VirtualBox for some time now in order to try out different versions of Linux, running Windows on my Mac, and so on. It’s free, runs on any x86 architecture, and just seems to work pretty well. So, that was the plan. I created the VM, loading on the latest Ubuntu Linux, made sure that had some basic software like Java and a few other components. Then I went through my checklist of how to get the right Ruby and Cucumber installed and in less than a half hour I had it running. Take a snapshot so that if I try to extend the image and mess it up I can back up. Voilà, the students can work without having to lose sleep over getting their system set up. There are other things they’ll lose sleep over that are much more important.

The VM approach, and the ability to snapshot and branch off of different snapshots makes life so much easier for me as a teacher and it will save the students a tremendous amount of time. I’m sure some of the uber-geeks in the class will set up the software on their systems because that’s in their DNA. However, for those who really want to concentrate on the course topics, they can now do that without the hassle of being a system administrator. I will definitely use this approach more in future courses.

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  1. As one of those students in your testing class, I would like to comment and say thanks for adopting this method, and writing about it! I hope to see more instructors using VMs to distribute pre-configured environments; it is wonderful not having to waste hours trying to wade through cryptic setup procedures.

  2. Thanks Taylor. It’s good to know that some of the things I do work.

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