serve fa assets from relative root

app/views/layouts/application.html.erb

@@ -21,6 +21,11 @@ with BigBlueButton; if not, see <http://www.gnu.org/licenses/>.
     <meta name="action-cable-url" content="<%= relative_root+Rails.configuration.action_cable.mount_path %>"/>
     <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
 
+    <% if relative_root != '/b' %>
+      <script src="https://use.fontawesome.com/5ec1c77c7b.js"></script>
+    <% else %>
+      <%= stylesheet_link_tag  'fa/gl-fa', media: 'all', 'data-turbolinks-track': 'reload' %>
+    <% end %>
     <%= stylesheet_link_tag    'application', media: 'all', 'data-turbolinks-track': 'reload' %>
     <%= javascript_include_tag 'application', 'data-turbolinks-track': 'reload' %>
     <link href="https://fonts.googleapis.com/css?family=Roboto:400,700" rel="stylesheet">

config/environments/production.rb

@@ -87,4 +87,6 @@ Rails.application.configure do
 
   # Do not dump schema after migrations.
   config.active_record.dump_schema_after_migration = false
+
+  config.relative_url_root = ENV['RAILS_RELATIVE_URL_ROOT'] || '/b'
 end