Recently, I needed to create a new Rails application, and now that I'm using NixOS and Nix, I had no idea about how to do it. Fortunately, Ruby development using Nix seemed solved, so I just needed a way to initialize a new Rails application with Nix and using its development environments.

This template will help you with the process, generating a new project with the latest version of Rails (5.0.1).

First of all, clone the project:

$ git clone https://github.com/areina/nix-new-rails-app.git my_new_rails_app

There is a script script/init that executes all the necessary steps to have your new shiny Rails application initialized. I will describe all the steps below, and you can execute them manually if you prefer.

1. Generate a Gemfile.lock with all necessary gems for creating a Rails app.

   $ nix-shell -p bundler --command "bundler lock"
   

2. Generate a gemset.nix with nix packages definitions for those gems.

   $ $(nix-build '<nixpkgs>' -A bundix)/bin/bundix
   

3. Initialize the rails app and generate a new Gemfile.lock with dependencies for this new app.

   $ nix-shell --command "rails new . --force --skip-bundle; bundler lock"
   

4. Generate a new gemset.nix with all package dependencies for running your app

   $ $(nix-build '<nixpkgs>' -A bundix)/bin/bundix
   

At this point, your app is initialized. You can enter to your isolated development environment and run for example the rails server:

$ nix-shell
[nix-shell:...] $ rails server
=> Booting Puma
=> Rails 5.0.1 application starting in development on http://localhost:3000
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.7.0 (ruby 2.3.3-p222), codename: Snowy Sagebrush
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://0.0.0.0:3000
Use Ctrl-C to stop

Visit http://localhost:3000 and you should see the Rails default page and in your shell something like this, confirming that we're using nix packages:

Started GET "/" for 127.0.0.1 at 2017-02-05 22:14:25 +0100
Processing by Rails::WelcomeController#index as HTML
  Parameters: {"internal"=>true}
  Rendering /nix/store/x5idkhdyk38i50fs4n6hbhv07ipm3vbz-rb/lib/ruby/gems/2.3.0/gems/railties-5.0.1/lib/rails/templates/rails/welcome/index.html.erb
  Rendered /nix/store/x5idkhdyk38i50fs4n6hbhv07ipm3vbz-rb/lib/ruby/gems/2.3.0/gems/railties-5.0.1/lib/rails/templates/rails/welcome/index.html.erb (3.5ms)
Completed 200 OK in 14ms (Views: 6.4ms | ActiveRecord: 0.0ms)

Now that you're ready for hacking your new Rails app, remember removing the .git directory to be detached of this repo, and start tracking your own changes. You can execute script/eject or do it manually:

$ rm -rf .git/
$ rm -rf script/
# And probably you will like to init your own history :-)
$ git init