Magnum needs a image in glance to use when it spawns masters and workers. In openstack stein, we need to use (the outdated) Fedora Atomic 29 image.
# Download image
wget http://ftp-stud.hs-esslingen.de/pub/Mirrors/alt.fedoraproject.org/atomic/stable/Fedora-29-updates-20191126.0/AtomicHost/x86_64/images/Fedora-AtomicHost-29-20191126.0.x86_64.raw.xz
# Decompress
xz -d Fedora-AtomicHost-29-20191126.0.x86_64.raw.xz
# Upload to glance. Note the properties. These are important
openstack image create \
--disk-format=raw \
--container-format=bare \
--file=Fedora-AtomicHost-29-20191126.0.x86_64.raw \
--min-disk 6 \
--property os_distro='fedora-atomic' \
--property hw_rng_model='virtio' \
--public \
--protected \
fedora-atomic-latest