Hosting a website on an IPv6 Pi part 2: PROXY protocol

March 10th, 2017 by

In our previous post, we configured an SSL website on an IPv6-only Raspberry Pi server, using our IPv4 to IPv6 reverse proxy service.

The one problem with this is that our Pi would see HTTP and HTTPS requests coming from the proxy servers, rather than the actual clients requesting them.

Historically, the solution to this problem is to have the proxy add X-Forwarded-For headers to the HTTP request, but this only works if the request is unencrypted HTTP, or an HTTPS connection that is decrypted by the proxy. One of the nice features of our proxy is that it passes encrypted HTTPS straight to your server: we don’t need your private keys on the proxy server, and we can’t see or interfere with your traffic.

Of course, this means that we can’t add X-Forwarded-For headers to pass on the client IP address. Enter PROXY protocol. With this enabled, our proxies add an extra header before the HTTP or HTTPS request, with details of the real client. This is easy to enable in our control panel:

You also need to configure Apache to understand and make use of the PROXY protocol header. This is a little more involved, as the necessary module isn’t currently packaged as part of the standard Apache distribution (although this is changing), so we need to download and build it ourselves. First some extra packages are needed:

apt-get install apache2-dev git

This will install a good number of packages, and take a few minutes to complete. Once done, you can download, install and build mod_proxy_protocol

git clone https://github.com/roadrunner2/mod-proxy-protocol.git
cd mod-proxy-protocol
make

At this point you should just be able to type make install but at time of writing, there seems to be some problem with the packaging. So instead do this:

cp .libs/mod_proxy_protocol.so /usr/lib/apache2/modules/

Now you can load the module:

echo "LoadModule proxy_protocol_module /usr/lib/apache2/modules/mod_proxy_protocol.so" > /etc/apache2/mods-available/proxy_protocol.load
a2enmod proxy_protocol

You also need to configure Apache to use it. To do this, edit /etc/apache2/sites-enabled/000-default.conf and replace each line that contains CustomLog with the following two lines:

	ProxyProtocol On
	CustomLog ${APACHE_LOG_DIR}/access.log "%a %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-agent}i\""

This tells Apache to use Proxy Protocol, and to use the supplied IP address in its log files. Now restart Apache:

systemctl reload apache2

Visit you website, and if all is working well, you should start seeing actual client IP addresses in the log file, /var/log/apache2/access_log:

93.93.130.44 - - [24/Feb/2017:20:13:25 +0000] "GET / HTTP/1.1" 200 10701 "-" "curl/7.26.0"

Trusting your log files

With the above configuration, we’ve told Apache to use the client IP address supplied by our proxy servers. What we haven’t done is told it that it can’t trust any random server that pitches up talking PROXY protocol. This means that it’s trivial to falsify IP addresses in our log files. To prevent this, let’s set up a firewall, so that only our proxy servers are allowed to connect on the HTTP and HTTPS ports. We use the iptables-persistent package to ensure that our firewall is configured when the server is rebooted.

apt-get install iptables-persistent

ip6tables -A INPUT -s proxy.mythic-beasts.com -p tcp -m tcp --dport 80 -j ACCEPT
ip6tables -A INPUT -s proxy.mythic-beasts.com -p tcp -m tcp --dport 443 -j ACCEPT
ip6tables -A INPUT -p tcp --dport 80 -j REJECT
ip6tables -A INPUT -p tcp --dport 443 -j REJECT

ip6tables-save

And we’re done! Our IPv6-only Raspberry Pi3 is now hosting an HTTPS website, and despite being behind a proxy server, we’re tracking real client IP addresses in our logs.