This hudson plugin will allow you to spin up hudson slave nodes on-demand using the Fog ruby library.
It addresses my immediate need for a cloud plugin that I can maintain, but it also serves as a template / proving ground for authoring hudson plugins in ruby.
to run, you need a the plugin development maven setup. To summarize, add the following to ~/.m2/settings.xml
<settings>
<pluginGroups>
<pluginGroup>org.jvnet.hudson.tools</pluginGroup>
</pluginGroups>
</settings>
check it out and run it:
git clone git://github.com/cowboyd/fog.hpi.git
cd fog.hpi
mvn hpi:run