You might have experienced one of these unpleasant situations: • You’re developing on a computer and you don’t have the admin rights to install a dependency. • It took you five hours to install the latest version of you favorite DB but your boss tells you the app will have to run on a previous version. • It took you two weeks to build a perfectly clean application... that only works on your machine. • The SysOp in charge of all launches hates you because your app is undeployable. Long story short, you already have or soon will spend, at some point in your life, as much time setting up your work environment as actually developing your app. Right now, you are probably developing a one-block app, with softwares and libraries installed directly in your development environment, or maybe in a virtual environment... Imagine if your application has to be deployed all over the world and you have to redevelop it for all existing platforms and OSs... Docker was created to satisfy this need for unification and normalisation: it makes it possible to split an application into several microservices, light, adaptable, universal and scalable, and it also gives the system administrators a great flexibility to deploy and scale up the app. This suite of projects on Docker will help you better understand this specific tool, but also the various aspects of applications development using microservices.s

I used this app: https://github.com/RailsApps/rails_apps_composer FOR 01_dockerfiles/ex02/