Bug 1687599

Openstack Ironic need to set the mac address of neutron port to the actual mac address of the hardware for DHCP/PXE deployment to work. When using pre-created neutron ports there is an issue where previously used ports cause a conflict when a new instance is scheduled onto the same baremetal hosts.

The same thing can happen when an error occur while spawning an instance. Nova will re-schedule, and the neutron port will end up with the mac address of the Ironic node last attempted to use. When a user tries to create another instance the same Ironic node can be selected, when it is the new instance will fail to build because Ironic tries to update the new instance's neutron port with the mac address of the neutron port associated with the instance that failed to build.

Example:

openstack port create --network private test-port1
openstack port create --network private test-port2
openstack server create \
   --image cirros-0.3.5-x86_64-disk \
   --port test-port1\
   --flavor baremetal \
   test-server
  openstack server delete test-server
openstack server create \
   --image cirros-0.3.5-x86_64-disk \
   --port test-port2 \
   --flavor baremetal \
   test-server
The second server create command fails with:
fault:
code: 500
created: '2018-04-29T12:21:37Z'
< .. snip .. >
message: 'Build of instance 5982f29a-3d48-4eb8-88ca-cf794c8f31dd aborted: Failure prepping block device.'

And in conductor log:
Apr 29 14:21:35 ironic-devstack.lab.example.com ironic-conductor[445]: ERROR ironic.common.neutron MacAddressInUseClient: Unable to complete operation for network 52497681-18f4-47de-b48e-1265799caea9. The mac address 52:54:00:53:b5:b9 is in use.