Merge branch 'sh-support-cdns' into 'master'

Support a configurable Rails asset_host to allow for CDNs

See merge request !12102

config/environments/production.rb

@@ -50,7 +50,7 @@ Rails.application.configure do
   # config.logger = ActiveSupport::TaggedLogging.new(SyslogLogger.new)
 
   # Enable serving of images, stylesheets, and JavaScripts from an asset server
-  # config.action_controller.asset_host = "http://assets.example.com"
+  config.action_controller.asset_host = ENV['GITLAB_CDN_HOST'] if ENV['GITLAB_CDN_HOST'].present?
 
   # Precompile additional assets (application.js, application.css, and all non-JS/CSS are already added)
   # config.assets.precompile += %w( search.js )

doc/administration/environment_variables.md

@@ -13,6 +13,7 @@ override certain values.
 
 Variable | Type | Description
 -------- | ---- | -----------
+`GITLAB_CDN_HOST`                          | string  | Sets the hostname for a CDN to serve static assets (e.g. `mycdnsubdomain.fictional-cdn.com`)
 `GITLAB_ROOT_PASSWORD`                     | string  | Sets the password for the `root` user on installation
 `GITLAB_HOST`                              | string  | The full URL of the GitLab server (including `http://` or `https://`)
 `RAILS_ENV`                                | string  | The Rails environment; can be one of `production`, `development`, `staging` or `test`
@@ -58,6 +59,9 @@ to the naming scheme `GITLAB_#{name in 1_settings.rb in upper case}`.
 
 ## Omnibus configuration
 
+To set environment variables, follow [these
+instructions](https://docs.gitlab.com/omnibus/settings/environment-variables.html).
+
 It's possible to preconfigure the GitLab docker image by adding the environment
 variable `GITLAB_OMNIBUS_CONFIG` to the `docker run` command.
 For more information see the ['preconfigure-docker-container' section in the Omnibus documentation](http://docs.gitlab.com/omnibus/docker/#preconfigure-docker-container).