HA Application Servers should have nginx running on them.

As per:

https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/files/gitlab-cookbooks/package/libraries/config/roles/application.rb

The application role only includes rails services (makes sense, as that's the "application"):

https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/files/gitlab-cookbooks/package/libraries/config/services.rb#L19

In 99.9% of HA deploys HA "Frontend Nodes" will also want a local copy of nginx unless they are using some exotic load balancing solution or something non-standard. These 5 sentences explain what 4 words of config are for. :D

(Roles are dope though, this is me expounding on the power of what roles make "look easy!")