Hey guys! How are you!

That's the second article of a series that teaches how to create a production ready Rails application. In this article we'll configure docker and docker compose.

Configuring docker

First thing we need to do is create a file called Dockerfile in the root path of the application.

The following snippet contains the file content:

FROM ruby:3.1.2-alpine3.16

RUN apk --update add postgresql-dev postgresql-client build-base tzdata libxslt-dev libxml2-dev

RUN mkdir /app

WORKDIR /app

This file creates a image that contains everything the application needs to run. To create this image docker follow this steps:

FROM ruby:3.1.2-alpine3.16

This line specifies that docker should download the following image from dockerhub and use it as base to run the following commands

RUN apk --update add postgresql-dev postgresql-client build-base tzdata libxslt-dev libxml2-dev

This instruction tells to docker install the following dependencies:

• build-base: To ensure certain gems can be compiled
• tzdata: Handle timezones
• libxslt-dev libxml2-dev: Nokogiri native dependencies
• postgresql-dev postgresql-client: Postgres related

RUN mkdir /app

Creates a folder called "/app"

WORKDIR /app

Tells docker that the folder "/path" is the main folder of the application.

Configuring docker compose

The first thing to do to configure docker-compose is create a file called docker-compose.yml in the root path of the application. This file should have the following content:

version: '3.9'

services:
  postgres:
    image: postgres:14.5-alpine
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: 123456
      PGDATA: /data/postgres
    volumes:
      - postgres:/data/postgres
    ports:
      - "5432:5432"
    networks:
      - postgres

  rails_guide:
    build: .
    volumes:
      - .:/app
    image: rails_guide
    container_name: rails_guide
    tty: true
    ports:
      - "3000:3000"
    environment:
      - DATABASE_NAME=app_development
      - DATABASE_USERNAME=user
      - DATABASE_PASSWORD=123456
      - DATABASE_HOST=postgres
    depends_on:
      - postgres
    networks:
      - postgres

networks:
  postgres:
    driver: bridge

volumes:
  postgres:

Executing docker

Now that everything is configured run the following command to create the containers:

docker-compose up -d

This command will create both containers and get it running

You can verify if everything is ok by running the following commando

docker ps

The output should looks like this:

Now run this command to go inside the container:

docker exec -it rails_guide sh

Setting up the database

You'll need to update the database configuration to mathces the docker environment, you'll need to change config/database.yml with the following content:

default: &default
  adapter: postgresql
  encoding: unicode
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  host: <%= ENV.fetch("DATABASE_HOST", "localhost") %>
  user: <%= ENV.fetch("DATABASE_USERNAME", "user") %>
  password: <%= ENV.fetch("DATABASE_PASSWORD", "123456") %>

development:
  <<: *default
  database: app_development

test:
  <<: *default
  database: app_test

production:
  <<: *default
  database: <%= ENV.fetch("DATABASE_NAME", "app_production") %>

To setup the database you'll need to run the following commands:

rails db:drop
rails db:create
rails db:migrate

Running the server

You can verify if everything is ok by starting the server by running the following command:

rails s -b 0.0.0.0

If everything is ok you'll see something like this:

You can see all code changes here