Max attachment size also needs a Web server configuration change

If you bump the max attachment size in the application settings, you also have to be sure the Web server is configured to accept a body of that size. With the omnibus install, you can do this in /etc/gitlab/gitlab.rb. For example:

nginx['client_max_body_size'] = "200m"

If you don't set this, the Web server may reject the file with a bit of an alarming message: "413 Request Entity Too Large".

Aside from fixing the scary HTML, possible solutions to improving this:

1. Put the max attachment size in gitlab.yml (and take it away from the application settings menu)
2. Document this better

Thoughts?