Use containers for Ruby on Rails development

Table of contents

Prerequisites

Complete Containerize a Ruby on Rails application.

Overview

In this section, you'll learn how to set up a development environment for your containerized application. This includes:

Adding a local database and persisting data
Configuring Compose to automatically update your running Compose services as you edit and save your code

Add a local database and persist data

You can use containers to set up local services, like a database. In this section, you'll update the compose.yaml file to define a database service and a volume to persist data.

In the cloned repository's directory, open the compose.yaml file in an IDE or text editor. You need to add the database password file as an environment variable to the server service and specify the secret file to use.

The following is the updated compose.yaml file.

services:
  web:
    build: .
    command: bundle exec rails s -b '0.0.0.0'
    ports:
      - "3000:3000"
    depends_on:
      - db
    environment:
      - RAILS_ENV=test
    env_file: "webapp.env"
  db:
    image: postgres:latest
    secrets:
      - db-password
    environment:
      - POSTGRES_PASSWORD_FILE=/run/secrets/db-password
    volumes:
      - postgres_data:/var/lib/postgresql/data

volumes:
  postgres_data:
secrets:
  db-password:
    file: db/password.txt

Note
To learn more about the instructions in the Compose file, see Compose file reference.

Before you run the application using Compose, notice that this Compose file specifies a password.txt file to hold the database's password. You must create this file as it's not included in the source repository.

In the cloned repository's directory, create a new directory named db and inside that directory create a file named password.txt that contains the password for the database. Using your favorite IDE or text editor, add the following contents to the password.txt file.

mysecretpassword

Save and close the password.txt file. In addition, in the file webapp.env you can change the password to connect to the database.

You should now have the following contents in your docker-ruby-on-rails directory.

.
├── Dockerfile
├── Gemfile
├── Gemfile.lock
├── README.md
├── Rakefile
├── app/
├── bin/
├── compose.yaml
├── config/
├── config.ru
├── db/
│   ├── development.sqlite3
│   ├── migrate
│   ├── password.txt
│   ├── schema.rb
│   └── seeds.rb
├── lib/
├── log/
├── public/
├── storage/
├── test/
├── tmp/
└── vendor

Now, run the following docker compose up command to start your application.

$ docker compose up --build

In Ruby on Rails, db:migrate is a Rake task that is used to run migrations on the database. Migrations are a way to alter the structure of your database schema over time in a consistent and easy way.

$ docker exec -it docker-ruby-on-rails-web-1 rake db:migrate RAILS_ENV=test

You will see a similar message like this:

console == 20240710193146 CreateWhales: migrating ===================================== -- create_table(:whales) -> 0.0126s == 20240710193146 CreateWhales: migrated (0.0127s) ============================

Refresh http://localhost:3000 in your browser and add the whales.

Press ctrl+c in the terminal to stop your application and run docker compose up again, the whales are being persisted.

Automatically update services

Use Compose Watch to automatically update your running Compose services as you edit and save your code. For more details about Compose Watch, see Use Compose Watch.

Open your compose.yaml file in an IDE or text editor and then add the Compose Watch instructions. The following is the updated compose.yaml file.

services:
  web:
    build: .
    command: bundle exec rails s -b '0.0.0.0'
    ports:
      - "3000:3000"
    depends_on:
      - db
    environment:
      - RAILS_ENV=test
    env_file: "webapp.env"

    develop:
      watch:
        - action: rebuild
          path: .
  db:
    image: postgres:latest
    secrets:
      - db-password
    environment:
      - POSTGRES_PASSWORD_FILE=/run/secrets/db-password
    volumes:
      - postgres_data:/var/lib/postgresql/data

volumes:
  postgres_data:
secrets:
  db-password:
    file: db/password.txt

Run the following command to run your application with Compose Watch.

$ docker compose watch

Any changes to the application's source files on your local machine will now be immediately reflected in the running container.

Open docker-ruby-on-rails/app/views/whales/index.html.erb in an IDE or text editor and update the Whales string by adding a exclamation marks.

-    <h1>Whales</h1>
+    <h1>Whales!</h1>

Save the changes to index.html.erb and then wait a few seconds for the application to rebuild. Go to the application again and verify that the updated text appears.

Press ctrl+c in the terminal to stop your application.

Summary

In this section, you took a look at setting up your Compose file to add a local database and persist data. You also learned how to use Compose Watch to automatically rebuild and run your container when you update your code.

Related information:

Next steps

In the next section, you'll take a look at how to set up a CI/CD pipeline using GitHub Actions.