We will continue with our opening problem. Our application is only accessible from one computer—our own. To fix this, we need to find all the differences that would exist between environments and abstract them out. We need this process to be automated. We cannot go through and find all references to localhost and change them out every time we want to deploy. We will follow the advice given by Twelve Factor App (http://12factor.net/).
Twelve Factor App was written by the people behind Heroku (https://www.heroku.com/). Heroku is a Platform as a Service (Paas), which means they can easily host and scale out application with very little modification to code. This ability is exactly what we want for this application. Twelve Factor App contains many best practices learned by the people at Heroku the hard way, through experience.
The main best practice we want from here is configuration. Configurations will be very different between environments...