Set up docker on Ruby on Rails application

Docker for Rails: From Development to Deployment (Complete Guide)

Docker simplifies building, shipping, and running applications in isolated containers. This guide covers:

✅ Running a Rails app with Docker
✅ Deploying to Docker Hub
✅ Running the app on another machine with zero setup

1. Setting Up a Rails App with Docker

Prerequisites

• Docker Desktop installed
• Docker Hub account

Step 1: Create a Rails App

rails new docker_rails_demo --database=postgresql
cd docker_rails_demo

Add a Welcome Page

rails generate controller Welcome index

Update config/routes.rb:

Rails.application.routes.draw do
  root 'welcome#index'
end

Step 2: Docker Configuration

ignore while pushing the code

.dockerignore

list env vars

.env

1. Write script for installation. Dockerfile

# Use official Ruby image (updated to a valid version)
FROM ruby:3.2.6-slim

# Install dependencies
RUN apt-get update -qq && apt-get install -y \
    build-essential \
    libpq-dev \
    nodejs \
    postgresql-client \
    && rm -rf /var/lib/apt/lists/*

# Set working directory
WORKDIR /siv_rails_app_dockerdemo

# Install gems
COPY Gemfile Gemfile.lock ./
RUN bundle install

# Copy application code
COPY . .

# Add a script to be executed every time the container starts
COPY entrypoint.sh /usr/bin/
RUN chmod +x /usr/bin/entrypoint.sh
ENTRYPOINT ["entrypoint.sh"]

# Expose port
EXPOSE 3001

# Start the main process
CMD ["rails", "server", "-b", "0.0.0.0"]

2. entrypoint.sh

#!/bin/bash
set -e

# Remove a potentially pre-existing server.pid for Rails
rm -f /siv_rails_app_dockerdemo/tmp/pids/server.pid

# Then exec the container's main process (what's set as CMD in the Dockerfile)
exec "$@"

3. docker-compose.yml

  version: "3.8"

  services:
    db:
      image: postgres:15
      environment:
        POSTGRES_PASSWORD: password
      volumes:
        - postgres_data:/var/lib/postgresql/data
      ports:
        - "5432:5432"

    web:
      build: .
      command: bash -c "rm -f tmp/pids/server.pid && rails server -b 0.0.0.0"
      volumes:
        - .:/siv_rails_app_dockerdemo
      ports:
        - "3001:3000"
      depends_on:
        - db
      environment:
        DATABASE_URL: postgres://postgres:password@db:5432/dockerrails_development

  volumes:
    postgres_data:

Step 3: Run the App

# Build containers
docker-compose build

# Start services
docker-compose up

Access: http://localhost:3001

Initialize the Database

docker-compose exec web rails db:create
docker-compose exec web rails db:migrate

2. Deploying to Docker Hub

1. Build & Tag the Image

docker build -t shivrajbadu/docker_rails_demo:1.0 .

2. Push to Docker Hub

docker login
docker push shivrajbadu/docker_rails_demo:1.0

3. Running the App on Another Machine

1. Create a New Directory

mkdir ~/docker_rails_deploy && cd ~/docker_rails_deploy

2. Add docker-compose.yml

version: "3.8"

services:
  db:
    image: postgres:15
    environment:
      POSTGRES_PASSWORD: password
    volumes:
      - postgres_data:/var/lib/postgresql/data

  web:
    image: shivrajbadu/docker_rails_demo:1.0
    command: bash -c "rm -f tmp/pids/server.pid && rails server -b 0.0.0.0"
    depends_on:
      - db
    environment:
      DATABASE_URL: postgres://postgres:password@db:5432/docker_rails_demo_production
      RAILS_ENV: production
    ports:
      - "3002:3000"

volumes:
  postgres_data:

3. Start the App

docker-compose up

Access: http://localhost:3002

Initialize DB (If Needed)

docker-compose exec web rails db:create db:migrate

Key Docker Commands Cheat Sheet

Command	Description
docker-compose --build	Build dependencies
docker-compose up	Start containers. Run the services and processes.
docker-compose down	Stop containers
docker-compose logs web	View Rails logs
docker-compose exec web bash	Enter container shell
docker-compose exec web rails c	Open Rails console
docker ps	List running containers, processes
docker push <image>	Push to Docker Hub
docker container ls	to see container list
docker-compose stop	to stop all the processes for later restart
docker-compose run website rake db:migrate db:seed RAILS_ENV=production	website means name of service to run rails app
docker-compose run --rm website rake db:create db:migrate	website is name of service
sudo docker run -i -t <image/id> /bin/bash	enter into bash shell
docker rmi 24a77bfbb9ee -f	forcefully remove image
docker rm $(docker ps -a -q)	remove all the containers

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Note: If you don’t have Docker running on your local machine, you need to replace localhost in the above URL with the IP address of the machine Docker is running on. If you’re using Docker Machine, you can run below cmd to find out the IP.

docker-machine ip “${DOCKER_MACHINE_NAME}”