Example wordpress cdn rewrite

<?php
/*
Plugin Name: CDN Rewrite
Plugin URI: http://blog.andrewshell.org/cdnrewrite
Description: Rewrite urls on page if behind a CDN
Author: Andrew Shell
Version: 1.0.0
Author URI: http://blog.andrewshell.org/
*/

if (0 == strcmp($_SERVER['HTTP_USER_AGENT'], 'Amazon CloudFront')) {
  $now     = time();
  $expires = strtotime('+1 hour', $now);
  header("Expires: " . gmdate(DATE_RSS,$expires) . "\n");

  add_filter( 'home_url', 'cdnrewrite_url', 100, 4 );
  add_filter( 'site_url', 'cdnrewrite_url', 100, 4 );
}

function cdnrewrite_url( $url, $path, $orig_scheme, $blog_id )
{
  return str_replace('blog.andrewshell.org', 'd11b8ym2xu437t.cloudfront.net', $url);
}