Recommendations (and Differences) between different Ruby on Rails Production Web Servers

Very soon I plan on deploying my first Ruby on Rails application to a production environment and I've even picked a webhost with all the managed server and Capistrano goodness you'd expect from a RoR provider.

The provider allows for Mongrel, Thin, Passenger & FastCGI web servers, which seems very flexible, but I honestly don't know the differences between them. I have looked into them some, but it all gets a bit much when they start talking about features and maximum simultaneous requests - and that this data seems to vary depending on who's publishing it.

I have looked at Passenger (on the surface) - which does seem very appealing to me - but I was under the impression that Passenger wasn't the actual webserver, and instead was more like a layer on top of Apache or nginx and managed spawned instances of the application (like a Mongrel cluster).

Can anyone please set me straight with the differences in layman's terms so as I can choose wisely (because anyone who's seen Indiana Jones and the Last Crusade knows what happens if you choose poorly).

Short answer

Go with Apache/Nginx + Passenger. Passenger is fast, reliable, easy to configure and deploy. Passenger has been adopted by a large number of big Rails applications, including Shopify.

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The long answer

Forget about CGI and FastCGI. In the beginning there were no other alternatives so the only way to run Rails was using CGI or the faster browser FastCGI. Nowadays almost nobody runs Rails under CGI. The latest Rails versions no longer provides .cgi and .fcgi runners.

Mongrel has been a largely adopted solution, the best replacement for CGI and FCGI. Many sites still use Mongrel and Mongrel cluster, however Mongrel project is almost dead and many projects already moved to other solutions (mostly Passenger). Also, a Mongrel based architecture is quite hard to configure because it needs a frontend proxy (thin, ngnix) and a backend architecture composed of multiple Mongrel instances.

Passenger has been gaining widespread attention since it was released. Many projects switched from Mongrel to Passenger for many reasons, including (but not limited to) easy deployment, maintainability and performance. Additionally, Passenger is now available for both Apache and Ngnix.

The simplest way to use Passenger is the Apache + Passenger configuration. One Apache installation and multiple Passenger processes.

If you need better performance and scalability, you can use Ngnix as a frontend proxy and forward all Rails requests to multiple backend servers, each one composed of Apache + Passenger. I'm not going into the technical details here, this solution is intended to be used by Rails projects with an high level of traffic.

Even more complex solutions include a combination of different levels including http proxies and servers. You can have an idea of what I'm talking about reading some internal details from GitHub and Heroku.

Right now, Passenger is the best answer for most Rails projects.