Even if you have your own hardware there are scenarios where you might want stronger isolation, increased density and/or heterogeneous deployments. All of which is achievable with Unikernels running on Xen.
How would unikernels running on Xen give you better density than containers (which are really just namespaced processes) running on a shared Unix kernel on bare metal? Wouldn't the Xen-based approach have more overhead?
This isn't supported yet, but unikernels on Xen don't currently switch address spaces (cr2 on x86). We're thinking about how to increase density by supporting process switching on Xen, which isn't hard, but needs to be done carefully.
Xen also supports memory sharing among VMs if running in a hardware container, and Hwanju Kim added support for "PVH" mode to MiniOS recently which unlocks this functionality in Mirage. Early days on this work, but fun ones, since we aren't bound by the compatibility constraints of Linux containers, but have access to the same hardware resources.
There are other approaches that yield Unikernels [1]. I don't quite understand your point about kernel mode and why that would be a problem under this scenario. The code is your own and you only use the OS components you require. The ASPLOS article has more detail on the approach and trade-offs [2].
Perhaps I'm wrong but I feel you've either (1) missed the point or (2) haven't actually looked at the references. Everything is written in a high-level language and the VM is an artefact produced as a result of the process (you don't debug on the VM, you debug the code that generated it).
Sure and then when production errors happen I'm left with having to deal with debugging a VM process rather than a User mode process :)
Enough can go wrong in the packaging and distribution that it's a real risk.
At the end of the unikernel generation pipeline I get a little Xen VM spit out that I can run. How do I debug this guy? It's running on a hypervisor but is essentially in a different environment. I'd love to be able to take code written in one environment and be 100% sure it'd work in another, but that ain't going to happen soon.
