Remote Proxy with Varnish

default.vcl

# Our origin backend
backend blogs {
    .host = "blogs.dev";
    .port = "8888";
}

# Our proxy backend
backend remote {
    .host = "proxy.local";
    .port = "8888";
}

sub vcl_recv {
    # Default to proxy
    set req.backend = remote;	

    # Only match what we explicitly want
    if (req.http.host ~ "blogs.dev") {
        set req.backend = blogs;
        return (lookup);
    }

    # Store the old host so we know where to go get something from
    set req.http.prehost=req.http.host;
    # And make sure Apache knows which vhost we want
    set req.http.host="proxy.local";

    return (lookup);
 }

sub vcl_fetch {
    set beresp.ttl = 0s; 
    set beresp.do_esi = true;
}

index.html

 <esi:include src="http://example.com/header.html" />
 <esi:include src="http://example.com/body.html" />
 <esi:include src="http://example.com/footer.html" />

proxy.php

<?php
$url = (isset($_SERVER['HTTP_PREHOST']) ? $_SERVER['HTTP_PREHOST'] : $_SERVER['HTTP_HOST']) . $_SERVER['REQUEST_URI'];

echo sprintf('<!--  Reverse Proxy got "%s"-->', $url) . PHP_EOL
     . curl_get($url, array(), array(CURLOPT_PROXY => '<username>:<password>@<proxy>:<port>')) . PHP_EOL
     . sprintf('<!-- // End reverseproxy get of "%s" -->', $url) . PHP_EOL;

/**
 * Send a GET requst using cURL
 * @param string $url to request
 * @param array $get values to send
 * @param array $options for cURL
 * @return string
 * @link http://au.php.net/manual/en/function.curl-exec.php#98628 
 */
function curl_get($url, array $get = array(), array $options = array())
{
    $defaults = array(
        CURLOPT_URL => $url. (strpos($url, '?') === FALSE ? '?' : ''). http_build_query($get),
        CURLOPT_HEADER => 0,
        CURLOPT_RETURNTRANSFER => TRUE,
        CURLOPT_TIMEOUT => 4
    );

    $ch = curl_init();
    curl_setopt_array($ch, ($options + $defaults));
    if( ! $result = curl_exec($ch))
    {
        trigger_error(curl_error($ch));
    }
    curl_close($ch);
    return $result;
}