The blueprint implementing traits for Placement provides a new library called os-traits that needs to be synchronizing what Placement knows about traits.
Basically, that library provides a list of known traits that Placement can support, and any new capabilities would require a synchronization between the library and the Placement DB.
As a consequence, os-traits becomes a dependency for placement service, and any upgrade of os-traits requires a os-traits sync command that updates the placement DB.
All the deployer impacts are written in :
Created a BZ  for adding os-traits library in RDO packages.
Since the design has changed, instead of having a separate placement-manage command to sync the traits from os-traits library to placement db,
the change https://review.openstack.org/#/c/469578/ sync os-traits library to placement db, whenever new version of library is released.
This is done, as the python-os-traits module is available in RDO packages and dependency for nova-distgit package was added to use this module in nova.
Thank you for the providing correct info and setting appropriate status.
I will make sure not to make such mistake again.
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.