Docker Compose with Rails

In this tutorial, learn how to integrate Dotenv Vault with Docker Compose and a Rails application.

Dockerfile

Create your Dockerfile in your rails application

# Dockerfile
FROM ruby:2.7.4
RUN apt-get update && apt-get install -y nodejs
WORKDIR /app
COPY Gemfile* .
RUN bundle install
COPY . .
EXPOSE 3000
CMD ["rails", "server", "-b", "0.0.0.0"]

example

Create your docker-compose.yml

version: "3.9"
services:
  db:
    image: postgres
    volumes:
      - ./tmp/db:/var/lib/postgresql/data
    environment:
      POSTGRES_PASSWORD: password
  web:
    build: .
    command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
    volumes:
      - .:/demo
    ports:
      - "3000:3000"
    depends_on:
      - db
    environment:
      SECRET_KEY_BASE: 1
      DOTENV_KEY: ${DOTENV_KEY}
      RAILS_ENV: ${RAILS_ENV}

example

Here’s an example of a simple welcome index page that runs on docker.

// welcome/index.html.erb
<h1>Welcome <%= ENV["HELLO"] %></h1>

example

Install dotenv-vault

Create your local .env file.

HELLO="Rails on docker compose"

Add dotenv-vault-rails gem to Gemfile

// Add 'dotenv-vault-rails' to Gemfile
gem 'dotenv-vault-rails'

example

Require dotenv-vault as early as possible in your Rails application. For a Rails application require dotenv-vault/load in application.rb

// config/application.rb
require 'dotenv-vault/load'

Build your rails application via docker by running

docker compose build

Test that it is working locally.

$ docker compose up

It says Hello Rails on docker compose at http://localhost:3000.

Build .env.vault

First set a production value for when we deploy. I set it to HELLO=Production. Run dotenv-vault open to edit production values.

$ npx dotenv-vault open production

Then build your localized encrypted .env.vault file.

$ npx dotenv-vault build

Great! Commit your .env.vault file to code. It is safe to do so. It is a localized encrypted vault of your environment variables.

Set DOTENV_KEY

Lastly, set the DOTENV_KEY on the docker run command.

Run npx dotenv-vault keys production to get your production decryption key.

$ npx dotenv-vault keys production
remote:   Listing .env.vault decryption keys... done

dotenv://:[email protected]/vault/.env.vault?environment=production

Set it for Docker run. The important part here is the -e flag.

$ RAILS_ENV=production DOTENV_KEY="dotenv://:[email protected]/vault/.env.vault?environment=production" docker compose up

That’s it!

Commit your changes to code and deploy your Docker image to your infrastructure.

When Docker runs, it will recognize the DOTENV_KEY, decrypt the .env.vault file, and load the production environment variables inside of Docker. If a DOTENV_KEY is not set (like during development on your local machine) it will fall back to regular dotenv.

It worked if you see the message ‘Loading env from encrypted .env.vault’.