New Rails App using Docker

README.md

Creating a new Rails app using docker

1. Create your project dir railsapp and copy the Dockerfile inside.
2. Comment all but first 3 lines in Dockerfile.
3. Run docker build -t railsapp:latest .
4. Once done, run docker run --rm -it -v $(pwd):/project railsapp:latest /bin/bash
5. Inside docker, run the following commands

   rails new railsapp --api --database=postgresql --skip-bundle
   mv railsapp/{*,.*} /project/
   exit

6. Then in the host, own everything back from root using sudo chown -R $USER:$USER .
7. Add the following in config/database.yml file

   default: &default
     # other stuff
     # adapter: ...
     # encoding: ...
     # pool: ...
     host: db
     username: postgres
     password: password
   

8. Uncomment previously commented lines in Dockerfile
9. Copy docker-compose.yml to your project folder
10. Then run the following docker commands:

    docker compose build
    docker compose up
    

11. Without closing the docker compose up running task, run in another terminal

    docker compose run web rails db:create
    

12. Your app should now be running at http://localhost:3000

Adding env file

It is a good practice to keep the configuration in a separate file inside the codebase. Fortunately, the variables specified in docker-compose.yml file, without no extra setup, will be subsituted with the variables specified inside the .env file (if they are not present in the environment variables already).

1. Add a new line .env at the end of .gitignore file if it is not present already. This .env file which we will create in the next step contains all the secrets and hence is added to .gitignore before creation!

2. Add a new .env file with the following contents:

   RAILS_APPNAME=railsapp
   RAILS_DEMO_POSTGRES_USERNAME=railsapp
   RAILS_DEMO_POSTGRES_PASSWORD=password
   RAILS_DEMO_POSTGRES_HOST=db
   

3. postgres docker image allows creating specific roles with the specified password using the entrypoint script. Add under db in docker-compose.yml,

   services:
   db:
     environment:
       - POSTGRES_USER=${RAILS_DEMO_POSTGRES_USERNAME}
       - POSTGRES_PASSWORD=${RAILS_DEMO_POSTGRES_PASSWORD}
   

4. All the environment variables inside .env file are required for our rails app and so, under web in docker-compose.yml add,

   services:
   web:
     env_file:
       - .env
   

5. Replace the hardcoded variables previously added in the database.yml file

   default: &default
     # other stuff
     # adapter: ...
     # encoding: ...
     # pool: ...
     host: <%= ENV["RAILS_DEMO_POSTGRES_HOST"] %>
     username: <%= ENV["RAILS_DEMO_POSTGRES_USERNAME"] %>
     password: <%= ENV["RAILS_DEMO_POSTGRES_PASSWORD"] %>
   

docker-compose.yml

version: '3'
services:
  db:
    image: postgres
    environment:
      POSTGRES_PASSWORD: password
  web:
    build: .
    command: bundle exec rails s -p 3000 -b '0.0.0.0'
    ports:
      - "3000:3000"
    depends_on:
      - db
    volumes:
      - ./:/railsapp

Dockerfile

FROM ruby:3.1
RUN apt update -qq && apt install -y nodejs postgresql-client
RUN gem install rails -v '7.0.3.1'

ARG APP=/railsapp
WORKDIR ${APP}
ADD Gemfile ${APP}/
RUN bundle install