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Getting Started with Dev Containers

After reading this guide, you will know:

The best way to read this guide is to follow it step by step. All steps are essential to run this example application and no additional code or steps are needed.

This guide helps you get set up with development containers (or dev containers for short) for a full-featured development environment. Dev containers are used to run your Rails application in a container, without needing to install Ruby or Rails or its dependencies directly on your machine. This is the fastest way to get your Rails application up and running.

This is an alternative to installing Ruby and Rails directly on your machine, which is covered in the Getting Started guides. Once you have completed this guide, you can continue building your application by following the Getting Started guide.

Setup and Installation

To get set up, you will need to install the relevant tools; Docker, VS Code and rails-new. We'll go into details about each one below.

Installing Docker

Dev containers are run using Docker, an open platform for developing, shipping, and running applications. You can install Docker by following the installation instructions for your operating system in the Docker docs.

Once Docker has been installed, launch the Docker application to begin running the Docker engine on your machine.

Installing VS Code

Visual Studio Code (VS Code) is an open source code editor developed by Microsoft. VS Code's Dev Containers extension allows you to open any folder inside (or mounted into) a container and take advantage of Visual Studio Code's full feature set. A devcontainer.json file in your project tells VS Code how to access (or create) a development container with a well-defined tool and runtime stack. It allows you to quickly spin up containers, access terminal commands, debug code, and utilize extensions.

You can install VS Code by downloading it from the website.

You can install the Dev Containers extension by downloading it from the marketplace.

Installing rails-new

rails-new generates a new Rails application for you without having to install Ruby on your machine. It uses Docker to generate the Rails application, thus allowing Docker to take care of installing the correct Ruby and Rails versions for you.

To install rails-new, follow the installation instructions in the README.

Creating the Blog Application

Rails comes with a number of scripts called generators that are designed to make your development life easier by creating everything that's necessary to start working on a particular task. One of these is the new application generator, which will provide you with the foundation of a fresh Rails application so that you don't have to write it yourself. The rails-new tool uses this generator to create a new Rails application for you.

NOTE: The examples below use $ to represent your terminal prompt in a UNIX-like OS, though it may have been customized to appear differently.

To use rails-new to generate your app, open a terminal, navigate to a directory where you have rights to create files, and run:

$ rails-new blog --devcontainer

This will create a Rails application called Blog in a blog directory.

TIP: You can see all of the command line options that the Rails application generator accepts by running rails-new --help.

After you create the blog application, switch to its folder:

$ cd blog

The blog directory will have a number of generated files and folders that make up the structure of a Rails application. Most of the work in this tutorial will happen in the app folder. For a full rundown of everything in your application see the full Getting Started guide.

Opening the Blog Application in a Dev Container

Our new Rails application comes with a dev container already configured and ready to use. We will use VS Code to spin up and work with our dev container. Start by launching VS Code and opening your application.

Once the application opens, VS Code should prompt you that it has found a dev container configuration file, and you can reopen the folder in a dev container. Click the green "Reopen in Container" button to create the dev container.

Once the dev container setup is complete, your development environment is ready to use, with Ruby, Rails, and all your dependencies installed.

You can open the terminal within VS Code to verify that Rails is installed:

$ rails --version
Rails 8.1.0

You can now continue with the Getting Started guide and begin building your Blog application. You will be working within VS Code, which serves as your entry point to your application's dev container, where you can run code, run tests, and run your application.