@tomasbrod, i am currently examining and making a list of what Google App Engine / Azure and Bluemix offers. Out of that list, i am going to separate, what's relatively easy to do, what's problematic, and what's impossible. I think it's a good starting point.

As for the Vapps, the standards differs from service to service, but you can look into it as "app level hypervisor" rather then os level. For example, you can deploy mysql on the OS, or as an Vapp. In second case, only the core requirements of an app are virtualized. To make it to the simplest level for the purpose of explanation, such virtualized system would not have anything other then what's required to run mysql. No ssh, not even bash. It's a way to save overhead that OS level virtualization comes with, as well allowing ease of migration. However that's just brief descriptions.