Initialize your project folder with git: git init

Create (and commit) your project files with a temporary ruby image:

docker run -it -v .:/rails ruby:3.2.2 /bin/bash
cd /rails
gem install rails
rails new .
exit

Copy the Dockerfile into a new Dockerfile.dev

1. Remove any environment variables
2. Modify bundle install step to only bundle install
3. Remove precompilation steps
4. Test it with docker build Dockerfile.dev .

Create a docker-compose.yml:

version: "3"
services:
   app:
     build:
       context: .
       dockerfile: Dockerfile.dev
     command: ./bin/rails server -b 0.0.0.0
   ports:
     - "3000:3000"
   volumes:
     - .:/rails

Configure the rails web console to work in docker in development.rb:

# Allow IRB in browser for a docker environment
config.web_console.permissions = '192.168.0.0/16'

Migrating to postgres:

1. Setup docker service

      version: "3"
      services:
        app:
          build:
            context: .
            dockerfile: Dockerfile.dev
          command: ./bin/rails server -b 0.0.0.0
          environment:
            DATABASE_HOST: db
            DATABASE_PASSWORD: password
          ports:
            - "3000:3000"
          volumes:
            - .:/rails
        db:
          image: postgres:15
          environment:
            POSTGRES_PASSWORD: password
          volumes:
            - db:/var/lib/postgresql/data
      volumes:
        db:
   

2. Run db docker service: docker compose up db

3. bin/rails db:system:change --to=postgresql

4. Modify ./config/database.yml:

      default: &default
        adapter: postgresql
        encoding: unicode
        host: <%= ENV["DATABASE_HOST"] %>
        password: <%= ENV["DATABASE_PASSWORD"] %>
        # For details on connection pooling, see Rails configuration guide
        # https://guides.rubyonrails.org/configuring.html#database-pooling
        pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
        username: postgres