Server Error 500 if Unicorn is Disabled When Using External Nginx/Passenger
The problem was firstly reported by @SpectralCoding in https://gitlab.com/gitlab-org/gitlab-ce/issues/2878 but he has closed the issue by himself.
A brief of the problem is: when using external nginx/passenger, Git over HTTPS will fail if the bundled unicorn server is disabled.
However, according to http://doc.gitlab.com/omnibus/settings/nginx.html#using-an-existing-passengernginx-installation , the unicorn should be disabled without causing any problems.