'openstack undercloud backup' sometimes fails with mistral error

Issue

• openstack undercloud backup sometimes fails with mistral error

• The following backup_undercloud.sh script is being ran :

#!/bin/bash
set -e
source /home/stack/stackrc
rm -f /tmp/backup_undercloud_*
swift delete undercloud-backups || true
swift delete undercloud-backups_segments || true
openstack undercloud backup --add-path /etc/ \
                            --add-path /var/log/ \
                            --add-path /root/ \
                            --add-path /var/lib/glance/ \
                            --add-path /var/lib/docker/ \
                            --add-path /var/lib/certmonger/ \
                            --add-path /var/lib/registry/ \
                            --add-path /srv/node/ && \
swift download --output /tmp/backup_undercloud_${1}.tar undercloud-backups `swift list undercloud-backups`
gzip /tmp/backup_undercloud_${1}.tar