Correct Client IP Address with a Reverse Proxy or Content Delivery Network (CDN)

Using a Reverse Proxy and/or a Content Delivery Network (CDN) has become common practice for Drupal and other Content Management Systems.

One inconvenient aspect of this is that your web server no longer gets the correct IP address, and neither does your application. The IP address is that of the machine that the reverse proxy is running on.

In Drupal, there is code in core that tries to work around this, by looking up the IP address in the HTTP header HTTP_X_FORWARDED_FOR, or a custom header that you can set.

For example, this would be in the settings.php of a server that runs Varnish on the same box.

$conf['reverse_proxy'] = TRUE;
$conf['reverse_proxy_addresses'] = array('127.0.0.1');

There is also this setting for Drupal 7.x in case your CDN puts the IP address in some other custom header:

// CloudFlare CDN 
$conf['reverse_proxy_header'] = 'HTTP_CF_CONNECTING_IP';

Only for the application, what about the web server?

But, even if you solve this at the application level (e.g. Drupal, or WordPress), there is still the issue that your web server is not logging the correct IP address. For example, you can't analyze the logs to know which countries your users are coming from, or identify DDoS attacks.

Apache RPAF module

There is a easy solution to this though: the Reverse Proxy Add Forward (RPAF).

What this Apache module does is extract the correct IP address, and uses that for Apache logs, as well hand over the correct IP address of the client in PHP's variable: $_SERVER['REMOTE_ADDR']

To install RPAF on Ubuntu 12.04 or later, use the command:

aptitude install libapache2-mod-rpaf

If you run the reverse proxy (e.g. Varnish) on same server as your web server and application, and do not use a CDN, then there is no need to do anything more.

However, if you run the reverse proxy on another server, then you need to change the RPAFproxy_ips line to include the IP addresses of these servers. For example, this will be the addresses for your Varnish servers which are front ending Drupal, then they are front ended by the CDN.

You do this by editing the file /etc/apache2/mods-enabled/rpaf.conf.

For example:

RPAFproxy_ips 10.0.0.3 10.0.0.4 10.0.0.5

CDN Client IP Header

If you are using a CDN, then you need to find out what HTTP header the CDN uses to put the client IP address, and modify RPAF's configuration accordingly.

For example, for CloudFlare, the header is CF-Connecting-IP

So, you need to edit the above file, and add the following line:

RPAFheader CF-Connecting-IP 

Drupal Reverse Proxy settings no longer needed

And finally, you don't need any of the above Reverse Proxy configuration in settings.php.

// $conf['reverse_proxy'] = TRUE;
// $conf['reverse_proxy_addresses'] = array('127.0.0.1');
// $conf['reverse_proxy_header'] = 'HTTP_CF_CONNECTING_IP';

Now, you have correct client IP addresses in Apache's logs, and inside Drupal as well.

What If RPAF Does Not Work?

If you have RPAF front ended directly by a CDN, without Varnish, then RPAF may not work for a yet unknown reason.

To overcome this, you have several other options.

Apache mod_remoteip

There is a small Apache module called mod_remoteip. This basically does the same thing as RPAF, but with simpler configuration.

Use the download link and save the file to the file named apache-2.2-mod_remoteip.c.

apxs2 -i -a -c apache-2.2-mod_remoteip.c

This should create the module's .so file in Apache's modules directory. It should also add the LoadModule directive in mods-available/remoteip.load, which should look like so:

LoadModule remoteip_module modules/mod_remoteip.so

Now add the RemoteIPHeader directive in a new file called mods-available/remoteip.conf

RemoteIPHeader X-Forwarded-For

If you are using CloudFlare CDN then you use:

RemoteIPHeader CF-Connecting-IP

Now, enable the module:

a2enmod remoteip

Then restart Apache:

service apache2 restart

If this does not work, then you can still do it using the next set of tricks:

Apache Access Log and Drupal Reverse Proxy Settings

We can force Apache to log the correct client IP address to the access log by adding this to the virtual host entry for your site (e.g. /etc/apache2/sites-enabled/example.com):

LogFormat "%{CF-Connecting-IP}i %l %u %t "%r" %>s %O "%{Referer}i" "%{User-Agent}i"" proxied

This takes the CF-Connecting-IP header from CloudFlare, and uses that instead of the IP address, which is of the proxy, not the originating client.

Then, under the "VirtualHost" stanza, you add this to use the custom proxied format you created above:

CustomLog ${APACHE_LOG_DIR}/access-example.com.log proxied

Then you need to enable the Drupal reverse proxy setting in settings.php:

$conf['reverse_proxy'] = TRUE;
$conf['reverse_proxy_header'] = 'HTTP_CF_CONNECTING_IP';

You don't need to add the reverse_proxy_addresses variable, because for CloudFlare there are too many of them.