Comment 4 for bug 1867013

Have you registered ironic nodes, and moved them to the available state? Do they have a 'resource_class' field set? Does the flavor have the required extra_specs to match the node's resource class and zero out the standard resource classes?

https://docs.openstack.org/ironic/stein/install/configure-nova-flavors.html

openstack hypervisor list will also tell you if the nodes are available for use by nova.