Comment 6 for bug 1928238

This issue does appear to be randomized based on juju upgrade-series complete ordering. This order of neutron-openvswitch completing post-series-upgrade before nova-compute is not affected by this bug. There must be something non-deterministic about the order of the post-series-upgrade hooks firing from juju that causes this race in some instances and not others, however, I wonder if neutron-openvswitch should actually mask openvswitch-switch.service during series upgrade, or allow for ovs to continue running while upgrade and reboot occur since nova may not be the only network path consuming the OVS service.

juju upgrade-series 1 complete
machine-1 complete phase started
machine-1 started unit agents after series upgrade
ntp/19 post-series-upgrade hook running
ntp/19 post-series-upgrade completed
neutron-openvswitch/1 post-series-upgrade hook running
neutron-openvswitch/1 post-series-upgrade completed
nrpe-host/17 post-series-upgrade hook running
nrpe-host/17 post-series-upgrade hook not found, skipping
lldpd/6 post-series-upgrade hook running
lldpd/6 post-series-upgrade completed
ceph-osd/1 post-series-upgrade hook running
ceph-osd/1 post-series-upgrade completed
filebeat/16 post-series-upgrade hook running
filebeat/16 post-series-upgrade completed
ceilometer-agent/1 post-series-upgrade hook running
ceilometer-agent/1 post-series-upgrade completed
hw-health/11 post-series-upgrade hook running
hw-health/11 post-series-upgrade completed
nova-compute-kvm/1 post-series-upgrade hook running
nova-compute-kvm/1 post-series-upgrade completed
landscape-client/19 post-series-upgrade hook running
landscape-client/19 post-series-upgrade hook not found, skipping
canonical-livepatch/6 post-series-upgrade hook running
canonical-livepatch/6 post-series-upgrade completed
telegraf/19 post-series-upgrade hook running
telegraf/19 post-series-upgrade completed
machine-1 series upgrade complete