Deploying apps is not that tough!
Over years, developers have standardized tool stacks, conventions and practices. Using standard stack and following conventions makes DevOps a lot easier.
Ubuntu (and most Linux distros) come with ruby preinstalled. Or they have ruby in their package repositories. You may use it if you want, but it is usually a few versions behind. For example, Ubuntu 14.04 comes with 1.9.3 which latest versions of Rails do not support.
You may also grab source code of ruby and compile manually or using tools like ruby-build.
Most developers prefer using rbenv or rvm to install and manage multiple versions of rubies. [Both have their pros and cons] (http://jonathan-jackson.net/rvm-and-rbenv). I personally prefer rbenv.
In this document, I will use rbenv.
Use whatever you are comfortable with and suits your use case.
Apache is more popular and has more features. Nginx is lighter and slightly faster.
In this document, I will use Apache.
Setting up Passenger is pretty straight forward and it is the preferred application server of Rails core team.
Unicorn and Puma are other popular application servers. EngineYard has put up a nice article comparing Passenger, Unicorn and Puma. Do check it out.
In this document, I will use Passenger along with Apache.
MySQL and PostgreSQL are two of the most popular database servers among Rails developers.
I will document instructions for both MySQL and PostgreSQL.
Although you can manually deploy application using git to update code, making necessary changes to server manually and restarting the server, it is preferred to use a deploy script that automates all these steps thereby reducing chances of error and making deploys faster.
Capistrano and Mina are two popular deploy automation tools. Up until a few months ago, Mina was significantly faster than Capistrano as Mina opened only one SSH connection per deploy as opposed to Capistrano which opened a new SSH connection per command. But Capistrano has catched up, and now it resuses SSH connections making deploy process much faster. Also, Capistrano supports multiple server deploys which Mina doesn’t.
In this document, I will use Capistrano as it is a more feature rich tool with a larger ecosystem.