title: .htaccess file redirect if not exists, remote file upload
body: <p>Server A - application</p>
  
  <p>Server B - static media from uploads, no app</p>
  
  <p>App on Server A processes the upload, validates and posts a job to convert it, after the conversion it's moved to Server B via copy (mounted drive) . Then the media file is loaded via a player on the page on Server A. </p>
  
  <p>I want to load the file via the remote url <a href="http://serverB/files/file1234.wtf" rel="nofollow noreferrer">http://serverB/files/file1234.wtf</a> and if the file is still not there yet (not yet copied), to transparently redirect it to <a href="http://serverA/tmp_files/file1234.wtf" rel="nofollow noreferrer">http://serverA/tmp_files/file1234.wtf</a></p>
  
  <p>How to do it with htaccess or any other way?</p>