Question

I have been playing around and evaluating other options to rails’ default WEBrick server and Thin was the most painless and clean thing which worked very well!!

which one of these Mongrel, Thin, WEBrick and Passenger would you recommend and why..?
are there any scalability perks(cluster friendly or configs which can handle some sort of scale) which come with any of these servers.. or should scalability even be a parameter while evaluating them?

Answer 1

Dipak already answered half of your question but let me clarify on things a little bit. (I am one of the Phusion Passenger authors.)

• WEBrick is a toy web server. Nobody uses it in anything but development because it performs poorly and is said to leak memory.
• You said Thin worked well. Have you already set it up in a reverse proxy configuration? Because that’s what people do in production scenarios. It is not safe to expose Thin (or Mongrel, or Unicorn) directly to the Internet.
• You may be interested in reading Ruby on Rails server options and the Phusion Passenger architectural overview for more etailed explanations.

When it comes to scalability, there’s not much difference. They all perform very similar in production, they all scale in about the same way, and any problems you encounter will most likely to be caused by your app or by Rails. Well, except for WEBrick, which you really shouldn’t use in production. You may see difference in hello world benchmarks, but that will be all. In production use most of the time will be spent in the app so any minor speed differences visible in hello world benchmarks will become completely invisible.

There are some subtleties to be aware of though.

• Phusion Passenger provides a feature called global queuing. It solves a specific problem, explained in detail in the manual. By default Nginx and Apache proxies requests in a round-robin manner so they suffer from this problem, while Phusion Passenger does not. There are ways to get around this when not using Phusion Passenger but they require specific configuration or the installation of additional web server modules.

• The I/O model may or may not be important depending on the nature of your application. Mongrel, Thin, Unicorn, they are all multi-process single-threaded. This works great for traditional web apps which looks up stuff in the local database and renders something, but sucks majorly for apps which perform a lot of HTTP API calls or otherwise have to wait a lot on I/O. Why Rails 4 Live Streaming is a Big Deal explains this in detail.

  Phusion Passenger is also multi-process single-threaded, but Phusion Passenger Enterprise supports multithreading. Phusion Passenger Enterprise is a commercial variant of the open source Phusion Passenger, with a variety of features useful for large-scale production environments.

• In large production environments, some features become important, e.g. rolling restarts, not showing anything wrong when a deployment failed, etc. Mongrel, Thin, Unicorn, Phusion Passenger, they all expose these features to some degree, but some require more admin effort than others. For example to implement rolling restarts in Mongrel and Thin, you need quite a lot of steps in your deployment scripts. Unicorn doesn’t require as many steps, but still significantly. This is where Phusion Passenger Enterprise shines: it takes all these features and turn them into a single config option. Turn the option on and the software takes care of the rest.

So, pick whatever option you think is best for your scenario.