Apache File Proxy

drupal-apache-file-proxy.conf

<IfModule mod_rewrite.c>
  RewriteEngine on
  # Force image styles that have local files that exist to be generated.
  RewriteCond %{REQUEST_URI} ^/sites/([.]*)/files/styles/[^\/]*/public/((.*))$
  RewriteCond %{DOCUMENT_ROOT}/sites/%1/files/%2 -f
  RewriteRule ^(.*)$ $1 [QSA,L]
  # Otherwise, send anything else that's in the files directory to the
  # production server.
  RewriteCond %{REQUEST_URI} ^/sites/(.*)/files/.*$
  RewriteCond %{REQUEST_URI} !^/sites/(.*)/files/(css|advagg-css|js|advagg-js)/.*$
  RewriteCond %{DOCUMENT_ROOT}%{REQUEST_FILENAME} !-f
  RewriteCond %{DOCUMENT_ROOT}%{REQUEST_FILENAME} !-d
  RewriteRule ^(.*)$ ##DOMAIN##/$1 [QSA,L]
</IfModule>