Rails Without Ruby.
When Rails 7.2 shipped, it quietly added something that makes life a lot easier for developers: native support for development containers (or dev containers for short).
If you’ve ever onboarded to a new Rails project, you probably know the drill: install the right version of Ruby, fight with system dependencies, get Node and a JavaScript bundler working, set up PostgreSQL… only then can you finally type rails new. It’s a lot, especially for beginners.
With devcontainers, that setup pain just disappears. A devcontainer is simply a Docker environment tailored for development. It comes with Ruby, Node, a database, Redis, and even Headless Chrome ready to go — all isolated from your machine. And starting with Rails 7.2, you don’t even have to write the config yourself. Just run:
rails new myapp --devcontainer
Rails will generate a .devcontainer folder for you, complete with Dockerfile, compose.yml and devcontainer.json to run everything out of the box. No Ruby required on your host machine.
For existing applications, a devcontainer command is now available:
rails devcontainer
This command only generates the .devcontainer folder and its files (Dockerfile, compose.yml, devcontainer.json). It doesn’t touch the rest of your app.
What You Need to Run a Devcontainer
The beauty of devcontainers is that your host machine doesn’t need Ruby, Node, or even a database installed. All you need is:
- A container runtime – usually that means Docker Desktop, but you can also use lighter or faster alternatives like Colima or OrbStack (which I use). They all provide the same underlying container support.
- VS Code – with the Dev Containers extension (or any other editor that understands devcontainers, but VS Code has the smoothest experience).
No rbenv, no rvm, no fiddling with Homebrew packages. Once your container runtime is running, VS Code will recognize the .devcontainer folder in your project and prompt you to “Reopen in Container”. From there, you’re inside a fully configured Rails environment.
So now you know: with Rails 7.2, a devcontainer can take care of your entire setup — no local Ruby required. All you need is Docker (or Colima, or OrbStack) and VS Code.
But that leaves us with one final question:
👉 How do you actually generate the devcontainer setup for a brand-new Rails app, or even for an existing one, if Ruby isn’t installed on your machine at all?
Rails New: The Standalone Rails Generator
When you usually type rails new, you’re relying on the rails gem that’s already installed on your system. But what if you don’t have Ruby or Rails installed locally? That’s where rails-new comes in.
Rails New is a standalone command-line tool published as a Ruby gem. Its whole job is to let you generate a brand-new Rails application without requiring a global Rails installation.
Installation
Go to the latest release and download the executable for your platform (not the source code). For example, on M1 macOS this would be rails-new-aarch64-apple-darwin.tar.gz.
Once the download is complete, unzip the .tar.gz file, which will create the rails-new executable. Move this executable somewhere on your system (for example, ~/bin or /usr/local/bin).
Finally, make sure it’s available in your terminal by adding it to your PATH. You can do this by adding a line like this to your shell config (~/.zshrc or ~/.bashrc):
export PATH="$PATH:/path-to-executable/rails-new"
After reloading your shell (source ~/.zshrc), you’ll be able to run rails-new from anywhere.
Usage
Once installed, it’s super simple:
rails-new myapp --devcontainer
This command uses Docker behind the scenes to generate your new Rails application—without requiring Ruby or Rails installed on your local machine.
The rails-new executable is just a wrapper around the official Rails application generator. That means you can pass any of the usual rails new options to it — exactly like you would if you had Rails installed locally.
You can see all of the command line options that the Rails application generator accepts by running rails-new --help.
Generating a Rails App with Just Docker
If you don’t want to download rails-new, you can still generate a new Rails app using nothing but Docker. The trick is to:
Start a Ruby container
From the directory where you want your project created, run:
docker run --rm -it -v "$PWD":/app -w /app ruby:3.4 bash
What this does:
• docker run --rm -it → run an interactive container that gets removed after exit.
• -v "$PWD":/app → mount your current directory into /app inside the container.
• -w /app → set the working directory.
• ruby:3.4 → use the official Ruby image (you can pick another version if you like).
Install Rails inside the container
Once inside the container, install Rails with:
gem install rails
Generate a new Rails application
Now create your app just like you normally would:
rails new myapp --devcontainer
This will generate a new myapp folder inside your mounted directory, complete with Rails 7.2’s .devcontainer setup.
Exit the container
Type exit to return to your host machine. Your Rails project is now available locally in the myapp folder.
Open it in VS Code and choose “Reopen in Container” — and you’re ready to run Rails, no Ruby installed on your machine. 🎉
Conclusion
Devcontainers change the way we think about setting up Rails. Instead of every developer wrestling with Ruby versions, Node, databases, and native dependencies on their own machine, you can now define a single, reproducible environment that works everywhere.
For teams, this means everyone shares the same setup — no more “works on my machine” problems, and onboarding new developers becomes as easy as cloning the repo and clicking “Reopen in Container”. Even if someone has never touched Rails before, they can be productive right away without having to fight through environment setup.
For individuals, devcontainers make it incredibly simple to experiment. Want to try Rails for the first time? Curious about a new release? You don’t need to install Ruby or worry about breaking your current system — just spin up the devcontainer and you have a fully isolated, ready-to-use environment in minutes.
The bottom line: you can now run Rails without ever installing Ruby locally. That makes Rails more accessible, more consistent, and a lot faster to get started with than ever before.
Give it a try today — spin up a Rails app with a devcontainer and see how easy it is to run Rails without Ruby installed locally. 🚀