This seems to work better and better on each major version. With current major version (11) I managed to keep an undercloud and controllers with less than the documented minimum on a virtual setup and it only started to hiccup after 2 weeks which I am fine with.
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.
https://access.redhat.com/errata/RHEA-2017:1245