Comment 1 for bug 1649902

Fuel runs haproxy via pacemaker (not vis systemd/upstart) and pacemaker runs haproxy in a separate network namespace. So haproxy does not cause any problems by listedning on 0.0.0.0 since it's listening in a separate network namespace. You can see it via "ip netns ls" command and then "ip netns exec haproxy ip a".

Did you try to restart haproxy via systemd/upstart? If so then you could face this problem. You should use pacemaker to control haproxy service.