\
This tutorial is intended to be a quick guide.

\
## Create a new Rails application via Docker with the following Command

```bash
docker run -it ruby:3.0.2 gem install rails bundler \
  && rails new exampleapp -d=postgresql --webpack:react --skip-coffee
```

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Once the application is created, go to the application directory. All application files will be found there.

\
```bash
cd exampleapp
```

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## Create a File called Dockerfile with the Following Content

```
// dockerfile

FROM ruby:3.0.2
RUN apt-get update -qq \
&& apt-get install -y curl build-essential libpq-dev \
 nodejs postgresql-client &&\
  curl -sL https://deb.nodesource.com/setup_10.x | bash - && \
  curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - && \
  echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list && \
  apt-get update && apt-get install -y nodejs yarn
ADD . /app
WORKDIR /app
RUN bundle install
EXPOSE 3000
CMD ["bash"]
```

\
This file will help Docker Compose build an image with all the needed dependencies installed to handle Rails. It will use Postgresql as a database engine and React bundled with webpack.

\
## Create a File Called docker-compose.yml With the Following Content

```yaml
version: '3.8'
services:
  db:
    env_file: .env
    image: postgres
  web:
    build: .
    command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
    volumes:
      - .:/app
    ports:
      - "3000:3000"
    depends_on:
      - db
    env_file: .env
    environment:
      RAILS_ENV: development
      RAILS_MAX_THREADS: 5
volumes:
  postgres:
```

\
## Create a .env File 

Add the following environment variables. Pay special attention to the `POSTGRES_` variable names since the **pg** image will need them for a proper setup, as well as the DATABASE_URL, which is needed by **web.** The query strings need to match with the other variable’s values. In the `DATABASE_URL`, the host is **db**, which is the name exposed by Docker Compose.

\
```
POSTGRES_DB=postgres
POSTGRES_USER=postgres
POSTGRES_PASSWORD=secret
DATABASE_URL=postgres://postgres:secret@db:5432/postgres
```

\
## Edit Database.yml

Edit the `config/database.yml` file and add `url: <%= ENV.fetch("DATABASE_URL") { '' } %>` Here is an example of a valid config file for this tutorial. Keep in mind the way you expose sensitive data and the environments you are building the Docker Compose for.

\
```yaml
default: &default
  adapter: postgresql
  encoding: unicode
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  url: <%= ENV.fetch("DATABASE_URL") { '' } %> # This is the line we added
development:
  <<: *default
  database: exampleapp_development
test:
  <<: *default
  database: exampleapp_test
production:
  <<: *default
  database: exampleapp_production
  username: exampleapp
  password: <%= ENV['EXAMPLEAPP_DATABASE_PASSWORD'] %>
```

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## Start the App

The application is ready. We can start our application now. We are adding the `--build` parameter the first time, so that Docker Compose builds the containers first.

\
```bash
docker-compose up --build
```

\
## Go to Localhost

We can now go to `http://localhost:3000` in our browser. We should see the “Yay! You’re on Rails!” screen.

\
 ![Yay! You're on Rails!](https://cdn.hackernoon.com/images/1T3oCWdeB5Ngves2c7TUliJbvAL2-yg0295q.png)

Now we can run commands (for example, generators and migrations) to evolve our application. We will now create a model with their controller and views, and then run a migration in this example.

\
The model will be **Coin**, and will have a name (string) and a value (float).

\
```bash
docker-compose run web rails g scaffold Coin name:string value:float \
 && rails db:migrate
```

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Here is a quick video of all that we have seen until now.

\
 ![](https://cdn.hackernoon.com/images/1T3oCWdeB5Ngves2c7TUliJbvAL2-3r1297y.gif)

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\


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