Mattermost deployment via chef : What is the MINIMAL/SIMPLEST same-server deployment option settings?

Suppose I make a stab at some gitlab.rb configuration changes. I run gitlabctl-reconfigure, then something fails. A minimal enabling of mattermost is one line, right? Just enable? The configuration page does not make it clear.

And yet I don’t see anything new if I only turn on that one line and set it true. The site is down until I disable and reconfigure. The documentation here is unclear to me:

The scenario I want is the one I imagine 99% of self-hosted instances of gitlab would want:

  1. I want a minimal configuration to get it going and try it.
  2. I don’t want anything other than defaults.

That case is not apparently documented being too obvious to the authors of the docs? only the exceptions and special cases get an example.

What are the MINIMAL deployment steps? Why does the gitlab-ctl reconfigure script return success and yet my site is down? Must I create a user and specify it?