On nightly I've tried creating a libvirt host and it worked well, please supply more information (logs, hash used to create the vm, compute resource provider..)

Deploying against a oVirt compute resource

If I manually set the IP address in the hash the host can be created. If I check its configuration in the GUI I can see that it hasn't inherited its primary interface subnet from its hostgroup. Getting the subnet_id from the hostgroup hash and adding it to the host hash allows the host to be created.

It subequently fails when SSH'ing into the box (windows, no sshd) which the WebGUI does not seem to do.

There seems to be some difference with hostgroups et al are dealt with when provisioning from an image vs' PXE?

The issue appears to be in set_hostgroup_defaults in Host::Managed - it only fills in subnet_id from the host group if pxe_build?. I don't think that's correct, as app/views/hosts/_unattended.html.erb for the UI uses a different check (whether the CR supports PXE building, which is still a bit odd, but works).

I don't quite follow why omitting the subnet_id was chosen as correct behavior for image based hosts. Is there a use case I'm missing?

It was probably from when image builds were only EC2, Rackspace etc, which supply their own IP address, so don't need a subnet_id.

Image builds on libvirt, VMware and oVirt were added more recently and work differently - more like PXE building, where we manage IP allocations.

Should the Compute Providers be able to override this behavior then maybe?

Yeah, it should probably be a method on the compute resource class to say what behaviour's expected. Thinking about it, there's something similar already - "provided_attributes" which is used to say which attrs are supplied by the compute resource, e.g. IP and MAC.

On a related note, it apepars that image based hosts dont remove their dhcp leases on deletion