Railgun is a web proxy system built for Cloudflare, that allows dynamic content for a website (such as the HTML) to be cached, while also allowing changes to the site to appear instantly. Railgun is currently available to customers with the Business and Enterprise plan, or via one of Cloudflare’s Optimised Partners. 

Railgun can especially help in the following situations:

• A lot of the visitors to the website are long way geographically from the website’s hosting.
• Your web hosts charge a lot by the GB for bandwidth. (i.e. you would like to minimise the amount you spend on that).
• You have a website with a lot of dynamic content, such as a very active blog or news source.

Unlike other Cloudflare features, it does require a program to be installed on or near the origin web server. Read more about the system requirements of Railgun and full instructions for installing and configuring Railgun. If you are the customer of an Optimized Partner of Cloudflare, you do not need to install. Your hosts will have done that for you.