What is Mongrel?
Mongrel is a super-fast and reliable HTTP server built specifically for Ruby applications like Rails.
Why would I want to use Mongrel for my Rails apps?
Because it's a dedicated web server that persistently holds your app in memory so its "always on" and ready to serve.
What are my alternatives?
With shared hosting, you'll commonly find Rails apps served semi-dynamically via FastCGI in cooperation with Apache. This means your app is held in memory for a little while, but when the FastCGI process is killed off it can take many seconds for the next dynamic hit to be served. Furthermore, in addition to Apache other web servers like LightTPD, Nginx, or LiteSpeed can be used, and each have their own advantages and disadvantages. However, Mongrel proxyed behind Apache2 has rapidly become the most popular Rails stack because it has proved stable and robust in large-scale production environments (e.g. www.rubyonrails.org uses it).
How can I setup and use Mongrel or a Mongrel Cluster with HostingRails.com?
We make it as simple as possible. You only need have a plan that includes 50MB of dedicated memory or more (think 50MB = 1 Mongrel - so 1 typical Mongrel comes free with the 'Professional' plan), then start up the Mongrel server(s) on the assigned port(s) we give you and we'll setup your mod_proxy_balancer so your app is ready to roll. See this step-by-step tutorial for more information.