Ironic has implemented similar rolling upgrade procedure to Nova in https://review.openstack.org/#/c/408556/. Now we need to run one more command on upgrades, starting with Ocata->Pike (!):
Otherwise the next upgrade (Pike->Queens, for example will fail).
We need updating both undercloud and overcloud bits to run it.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.