Deploy a Rails App to Fly.io

Deploy a Rails app with an encrypted .env.vault file to Fly.io.

Find a complete code example on GitHub for this guide.

Initial setup

Install Rails.

gem install rails

Create a new Rails project.

rails new yourapp

Edit config/routes.rb and set root to www#index.

config/routes.rb

Rails.application.routes.draw do
  get "up" => "rails/health#show", as: :rails_health_check
  root "www#index"
end

Create app/controllers/www_controller.rb.

app/controllers/www_controller.rb

class WwwController < ApplicationController
  def index
  end
end

Create app/views/www/index.html.erb.

app/views/www/index.html.erb

Hello <%= ENV["HELLO"] %>.

Commit that to code and push it to Fly.io.

brew install flyctl
flyctl launch
flyctl deploy --remote-only --no-cache

yourapp.fly.dev

Once deployed, your app will say 'Hello .' as it doesn't have a way to access the environment variable yet. Let's do that next.

Install dotenv-vault-rails

Add dotenv-vault-rails to the top of your Gemfile.

Gemfile

source "https://rubygems.org"
ruby "3.1.3"
gem "dotenv-vault-rails", require: "dotenv-vault/rails-now"
gem "rails", "~> 7.1.1"
...

bundle install

Create a .env file in the root of your project.

.env

# .env
HELLO="World"

Try running it locally.

bin/rails server
=> Booting Puma
=> Rails 7.1.1 application starting in development
* Listening on http://127.0.0.1:3000
* Listening on http://[::1]:3000

It should say Hello World.

Great! ENV now has the keys and values you defined in your .env file. That covers local development. Let's solve for production next.

Build .env.vault

Push your latest .env file changes and edit your production secrets. Learn more about syncing

npx dotenv-vault@latest push
npx dotenv-vault@latest open production

Use the UI to configure those secrets per environment.

www.dotenv.org

Then build your encrypted .env.vault file.

npx dotenv-vault@latest build

Its contents should look something like this.

.env.vault

#/-------------------.env.vault---------------------/
#/         cloud-agnostic vaulting standard         /
#/   [how it works](https://dotenv.org/env-vault)   /
#/--------------------------------------------------/

# development
DOTENV_VAULT_DEVELOPMENT="/HqNgQWsf6Oh6XB9pI/CGkdgCe6d4/vWZHgP50RRoDTzkzPQk/xOaQs="
DOTENV_VAULT_DEVELOPMENT_VERSION=2

# production
DOTENV_VAULT_PRODUCTION="x26PuIKQ/xZ5eKrYomKngM+dO/9v1vxhwslE/zjHdg3l+H6q6PheB5GVDVIbZg=="
DOTENV_VAULT_PRODUCTION_VERSION=2

Set DOTENV_KEY

Fetch your production DOTENV_KEY.

npx dotenv-vault@latest keys production
# outputs: dotenv://:[email protected]/vault/.env.vault?environment=production

Set DOTENV_KEY on Fly.io.

flyctl secrets set RAILS_ENV=production DOTENV_KEY='dotenv://:[email protected]/vault/.env.vault?environment=production'

Deploy

Commit those changes safely to code and deploy again.

flyctl deploy --remote-only --no-cache

That's it! On deploy, your .env.vault file will be decrypted and its production secrets injected as environment variables‚ just in time.

yourapp.fly.dev

You'll know things worked correctly when you see Loading env from encrypted .env.vault in your logs. If a DOTENV_KEY is not set (for example when developing on your local machine) it will fall back to standard dotenv functionality.

flyctl logs

You succesfully used the new .env.vault standard to encrypt and deploy your secrets. This is much safer than scattering your secrets across multiple third-party platforms and tools. Whenever you need to add or change a secret, just rebuild your .env.vault file and redeploy.