Recommended approach & tools to provision a VM instance(s) from node.js?

I am trying to implement a 'lab in the cloud' to allow people to have a sandbox to experiment and learn in; i.e. for devops (chef/puppet), installing or configuring software etc. I have a node.js server implementation to manage this and looking for sane and reasonable ways to attack this problem.

The options are bewilderingly diverse: puppet or chef directly, or vagrant seems appropriate. But Openstack, cloudfoundry, Amazon EC2 also provide their own feature sets. Ideally a micro-cloud solution (multiple VM's per instance) would be ideal as there isn't going to be any large computational load.

Suggestions most appreciated.

Cheers