On hosted systems with limited disk space, you might occasionally want to archive files out to Amazon S3 (or some other filer). This would usually result in URLs changing, though, so the ideal situation would be to have Apache simply proxy the request through to your filer if it cannot find the file on disk
This snippet checks for the file within the document root and if it does not exist, sends a request our to an S3 bucket
SSLProxyEngine On
RewriteEngine On
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteRule ^/(.*)$ https://s3.[amazonregion].amazonaws.com/[yourbucketname]/$1 [P,QSA,L]
SSLProxyEngine On
RewriteEngine On
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteRule ^/(.*)$ https://s3.eu-west-3.amazonaws.com/examplebucket/$1 [P,QSA,L]