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Purely multi-threaded. Nowadays the Ruby ecosystem has excellent multithreading support, so this I/O model has become very viable. Multithreading allows high I/O concurrency, making it suitable for both short-running and long-running blocking I/O workloads. The programmer is more likely to introduce concurrency bugs, but luckily most web frameworks are designed in such a way that this is still very unlikely. One thing to note however is that the MRI Ruby interpreter cannot leverage multiple CPU cores even when there are multiple threads, due to the use of the Global Interpreter Lock (GIL). You can work around this by using multiple multi-threaded processes, because each process can leverage a CPU core. JRuby and Rubinius have no GIL, so they can fully leverage multiple cores in a single process.
Hybrid multi-threaded multi-process. Primarily implemented by Phusion Passenger Enterprise 4 and later. You can easily switch between single-threaded multi-process, purely multithreaded, or perhaps even multiple processes each with multiple threads. This model gives the best of both worlds.
Evented. This model is completely different from the previously mentioned model. It allows very high I/O concurrency and is therefore excellent for long-running blocking I/O workloads. To utilize it, explicit support from the application and the framework is required. However all the major frameworks like Rails and Sinatra do not support evented code. This is why in practice a Thin process still cannot handle more than 1 request at a time, making it effectively behave the same as the single-threaded multi-process model. There are specialized frameworks that can take advantage of evented I/O, such as Cramp.
An article was recently posted on the Phusion blog about optimally tuning the number of processes and threads given your workload. See Tuning Phusion Passenger's concurrency settings.
Capistrano
Capistrano is something completely different. In all the previous sections, "deployment" refers to the act of starting your Ruby app in an application server, so that it becomes accessible to visitors, but before that can happen one typically needs to do some preparation work, such as:
Uploading the Ruby app's code and files to the server machine.
Installing libraries that your app depends on.
Setting up or migrating the database.
Starting and stopping any daemons that your app might rely on, such as Sidekiq/Resque workers or whatever.
Any other things that need to be done when you're setting up your application.
In the context of Capistrano, "deployment" refers to doing all this preparation work. Capistrano is not an application server. Instead, it is a tool for automating all that preparation work. You tell Capistrano where your server is and which commands need to be run every time you deploy a new version of your app, and Capistrano will take care of uploading the Rails app to the server for you and running the commands you specified.
Capistrano is always used in combination with an application server. It does not replace application servers. Vice-versa, application servers do not replace Capistrano, they can be used in combination with Capistrano.
Of course you don't have to use Capistrano. If you prefer to upload your Ruby app with FTP and manually running the same steps of commands every time, then you can do that. Other people got tired of it, so they automate those steps in Capistrano.
B.原文的翻译
翻译的资料。
Ruby on rails 服务器选择
一，Apache vs Nginx
他们都是web服务器，都能伺服静态文件，利用恰当的模块也能伺服动态的web应用。Apache更加流行，拥有更多的功能；Nginx则相对小巧、快速、功能少。
让Apache 和 Nginx 来伺服 Ruby 服务器都不是开箱即用（out-of-the-box）的，为此你需要使用另外的插件来组合他们。