I wanted to run my entire WordPress site through a CDN so this is what I had to do to make it work. cdn-integration.php is a plugin file that you shouldn't have to change. wp-config.php is some configuration details you'll need to put in wp-config.php Most CDNs let you control the TTL of how long to hold on to assets from the caching headers set…

cdn-integration.php

<?php
/*
Plugin Name: RH CDN Integration
Description: Making Origin Pull Work. Heavilty inspired by https://github.com/markjaquith/WP-Stack/blob/master/WordPress-Dropins/wp-stack-cdn.php
Version: 0.1
Author: Russell Heimlich
Author URI: http://www.russellheimlich.com
*/

// Convenience methods
if(!class_exists('RH_Plugin')){class RH_Plugin{function hook($h){$p=10;$m=$this->sanitize_method($h);$b=func_get_args();unset($b[0]);foreach((array)$b as $a){if(is_int($a))$p=$a;else $m=$a;}return add_action($h,array($this,$m),$p,999);}private function sanitize_method($m){return str_replace(array('.','-'),array('_DOT_','_DASH_'),$m);}}}

// The plugin
class RH_CDN_Plugin extends RH_Plugin {
	public static $instance;
	public $site_domain;
	public $cdn_domain;

	public function __construct() {
		self::$instance = $this;
		if( defined( 'FROMCDN' ) && FROMCDN ) {
			$this->hook( 'plugins_loaded' );
		}
	}

	public function plugins_loaded() {
		if ( !is_admin() ) {
			$this->hook( 'template_redirect' );
			$this->hook( 'redirect_canonical' );
			$this->hook( 'rh_cdn_content', 'filter' );
			$this->hook ( 'wp_footer', 999 );
			
			$this->site_domain = 'http://' . parse_url( get_bloginfo( 'url' ), PHP_URL_HOST );
			$this->cdn_domain = RH_CDN_DOMAIN; //Constant defined in wp-config.php
			
			// These are optional but they rewrite JS/CSS URLs that are loaded with wp_enque_* stripping the query string and adding a human readable date before the filename.
			// More details are available at https://forrst.com/posts/CDN_Friendly_CSS_and_JS_URLs_in_WordPress-IZn
			$this->hook( 'script_loader_src', 'cache_busting_file_src' );
			$this->hook( 'style_loader_src', 'cache_busting_file_src' );
		}
	}

	public function filter( $content ) {
		return str_replace( $this->site_domain, $this->cdn_domain, $content );
	}

	public function template_redirect() {
		ob_start( array( $this, 'ob' ) );
	}

	public function ob( $contents ) {
			return apply_filters( 'rh_cdn_content', $contents, $this );
	}

	public function redirect_canonical( $redirect_url, $requested_url ) {
		
		$no_port = preg_replace('/:\d+/i', '', $requested_url ); //Strip port numbers from the requested URL otherwise this could throw the site into an infinite redirect loop.
		if( $no_port != $redirect_url ) {
			return $redirect_url;
		}

		if( is_user_logged_in() || $_SERVER['QUERY_STRING'] || $no_port == $redirect_url ) {
			return false;
		}

		return $redirect_url;
	}
	
	public function wp_footer() {
		date_default_timezone_set( get_option('timezone_string') );
		echo "\n\t" . '<!-- Cached by CDN, Generated: ' . date( 'Y-m-d g:i:s a T') . ' -->' . "\n";
	}
	
	/*
	Rewrites CSS and JavaScript urls that are enqueued via the proper WordPress functions. It adds a date of when the file was last modified before the file name for cacheing efficeny.
	
	Requires the following in the .htaccess file:
	RewriteRule ^(.+)/\d.+/(.+)\.(js|css)$ $1/$2.$3 [L]
	*/
	
	public function cache_busting_file_src( $src, $handle ) {
		global $wp_scripts;
		
		//Strip out query strings.
		$src = explode('?', $src);
		$src = $src[0];
		
		//Check if script lives on this domain. Can't rewrite external scripts, they won't work.
		if( !strstr( $src, $wp_scripts->base_url ) || strstr( $src, 'wp-include' ) ) {
			return $src;
		}
			
		$regex = '/' . preg_quote($wp_scripts->base_url, '/') . '/';
		$path = preg_replace($regex, '', $src);
		
		//If the folder starts with wp- then we can figure out where it lives on the filesystem.
		if( strstr($path, '/wp-') ) {
			$file = untrailingslashit(ABSPATH) . $path;
		}
		
		//If the folder starts with /wp-content/themes and the COMPRESS_THEME_CSS constant is true, modify the path to point to the minified CSS. Note: Minification needs to happen when changes are deployed via a seperate script.
		if( strstr($path, '/wp-content/themes') && strstr($path, '/css') && defined('COMPRESS_THEME_CSS') && constant('COMPRESS_THEME_CSS') ) {
			$file_parts = pathinfo($file);
			$file = $file_parts['dirname'] . '/' . $file_parts['filename'] . '.min.' . $file_parts['extension'];
			
			$src_parts = pathinfo($src);
			$src = $src_parts['dirname'] . '/' . $src_parts['filename'] . '.min.' . $src_parts['extension'];
		}
		
		if( !file_exists($file) ) {
			return $src;
		}
		
		$time = 0; //Just in case something goes wrong...
		$time = date( 'Y-m-d_g:i', filemtime($file) );
		
		$path_parts = pathinfo($src);
		$new_path = $time . '/' . $path_parts['basename'];
		$src = preg_replace('/' . preg_quote($path_parts['basename'], '/') . '/i', $new_path, $src);
		
		return $src;
	}
}

new RH_CDN_Plugin;

wp-config.php

//Add the following code to your wp-config.php file somewhere before the /* Stop Editing comment*/

//Tells WordPress what the IP of the user requesting the page is instead of the IP of the load balancer or CDN.
if ( isset($_SERVER['HTTP_X_FORWARDED_FOR']) && !empty($_SERVER['HTTP_X_FORWARDED_FOR']) ) {
	$FWD_IP = explode( ",", $_SERVER['HTTP_X_FORWARDED_FOR'] );
	$_SERVER['REMOTE_ADDR'] = trim( $FWD_IP[0] );
} 

if( strpos( $_SERVER['REQUEST_URI'], '/wp-admin/') === FALSE ||
	strpos( $_SERVER['REQUEST_URI'], '/wp-login.php/') === FALSE
 ) {

	define('RH_CDN_DOMAIN', 'http://www.russellheimlich.com'); //Define the URL that goes through your CDN.
	if( isset($_GET['cdn']) || ( isset($_SERVER['HTTP_VIA']) && !empty($_SERVER['HTTP_VIA']) ) ) { //Some condition to determine the request came from the CDN. The HTTP VIA header is a good one.
		define('WP_HOME', 'http://russellheimlich.com/blog');
		define('WP_SITEURL', 'http://russellheimlich.com/blog');
		define( 'FROMCDN', TRUE ); 
	}

}

Hi,

Would this still work on current wordpress version?
I'm using keycdn and let's encrypt ssl. I get the green padlock all fine and the site works but I can't login to the site to edit or add new content. it's driving me crazy.