The metadata-api still loads pieces of nova-network even when using neutron=True.
Specifically, it is still loading linuxnet_interface_driver and it is adding in ACCEPT rules with iptables to allow the metadata port. While this may make sense with nova-network, it doesn't make sense for an api to be messing with iptables.
Since neutron uses metadata-api through its proxy, it cannot be said that the metadata-api is purely a nova-network thing.
The MetadataManager class that is loaded makes note of the fact that all the class does is add that ACCEPT rule [0]. Previously in Newton I was able to work around this by overriding the MetadataManager class with 'nova.manager.Manager', that that option was removed in Ocata [1]. Now the 'nova.api.manager.MetadataManager' name is hardcoded [2] and requires modifying nova source.
TL;DR when using the metadata-api, bits of nova-network are still loaded when they shouldn't be.
[0] https://github.com/openstack/nova/blob/4f91ed3a547965ed96a22520edcfb783e7936e95/nova/api/manager.py#L24
[1] https://github.com/openstack/nova/blob/stable/newton/nova/conf/service.py#L51
[2] https://github.com/openstack/nova/blob/065cd6a8d69c1ec862e5b402a3150131f35b2420/nova/service.py#L60
Should be fixed