In this article I will go through the steps required to install and configure Duo Security with Ubuntu Server for two factor authentication. This can be adapted to apply to SSH log-ons, sudo access, etc. The Linux PAM (pluggable authentication modules) make this easy to implement and customise.
I currently have this implemented on my Ubuntu 14.04 x64 LTS Server and it works really well.
In this article I will briefly go through instructions on installing mod_cloudflare on an Ubuntu 14.04 server running Apache 2.4.
The reason we need the mod_cloudflare module is because Cloudflare acts as a reverse proxy meaning that visitor IP addresses in your access logs (/var/log/apache2/access.log) will appear to come from any one of Cloudflare’s IP addresses; all of which they make available here.