Comment 13 for bug 1880610

charm-openstack-dashboard has its own haproxy.cfg template that it's not from charmhelpers.
The template uses `listen` for dash_insecure and dash_secure and as the documentation says[0]:

A "listen" section defines a complete proxy with its frontend and backend
parts combined in one section. It is generally useful for TCP-only traffic.

[0] http://cbonte.github.io/haproxy-dconv/1.6/configuration.html#4