Containerize a Ruby on Rails application

Table of contents

Prerequisites

  • You have installed the latest version of Docker Desktop.
  • You have a Git client. The examples in this section show the Git CLI, but you can use any client.

Overview

This section walks you through containerizing and running a Ruby on Rails application.

Get the sample application

The sample application uses the popular Ruby on Rails framework.

Clone the sample application to use with this guide. Open a terminal, change directory to a directory that you want to work in, and run the following command to clone the repository:

$ git clone https://github.com/falconcr/docker-ruby-on-rails.git

Initialize Docker assets

Now that you have an application, you can create the necessary Docker assets to containerize your application. You can use Docker Desktop's built-in Docker Init feature to help streamline the process, or you can manually create the assets.

docker init, the command for bootstrapping the Docker-related assets for a project, does not yet support the Ruby programming language. This means that if you are working with Ruby, you'll need to create Dockerfiles and other related configurations manually.

Inside the docker-ruby-on-rails directory, create the following files:

Create a file named Dockerfile with the following contents.

Dockerfile
# syntax=docker/dockerfile:1

# Use the official Ruby image with version 3.2.0
FROM ruby:3.2.0

# Install dependencies
RUN apt-get update -qq && apt-get install -y \
  nodejs \
  postgresql-client \
  libssl-dev \
  libreadline-dev \
  zlib1g-dev \
  build-essential \
  curl

# Install rbenv
RUN git clone https://github.com/rbenv/rbenv.git ~/.rbenv && \
  echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc && \
  echo 'eval "$(rbenv init -)"' >> ~/.bashrc && \
  git clone https://github.com/rbenv/ruby-build.git ~/.rbenv/plugins/ruby-build && \
  echo 'export PATH="$HOME/.rbenv/plugins/ruby-build/bin:$PATH"' >> ~/.bashrc

# Install the specified Ruby version using rbenv
ENV PATH="/root/.rbenv/bin:/root/.rbenv/shims:$PATH"
RUN rbenv install 3.2.0 && rbenv global 3.2.0

# Set the working directory
WORKDIR /myapp

# Copy the Gemfile and Gemfile.lock
COPY Gemfile /myapp/Gemfile
COPY Gemfile.lock /myapp/Gemfile.lock

# Install Gems dependencies
RUN gem install bundler && bundle install

# Copy the application code
COPY . /myapp

# Precompile assets (optional, if using Rails with assets)
RUN bundle exec rake assets:precompile

# Expose the port the app runs on
EXPOSE 3000

# Command to run the server
CMD ["rails", "server", "-b", "0.0.0.0"]

Create a file named compose.yaml with the following contents.

compose.yaml
services:
  web:
    build: .
    command: bundle exec rails s -b '0.0.0.0'
    volumes:
      - .:/myapp
    ports:
      - "3000:3000"

Create a file named .dockerignore with the following contents.

.dockerignore
git
.gitignore

# Created by https://www.gitignore.io/api/git,ruby,rails,jetbrains+all
# Edit at https://www.gitignore.io/?templates=git,ruby,rails,jetbrains+all

### Git ###
# Created by git for backups. To disable backups in Git:
# $ git config --global mergetool.keepBackup false
*.orig

# Created by git when using merge tools for conflicts
*.BACKUP.*
*.BASE.*
*.LOCAL.*
*.REMOTE.*
*_BACKUP_*.txt
*_BASE_*.txt
*_LOCAL_*.txt
*_REMOTE_*.txt

### JetBrains+all ###
# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio and WebStorm
# Reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839

# User-specific stuff
.idea/**/workspace.xml
.idea/**/tasks.xml
.idea/**/usage.statistics.xml
.idea/**/dictionaries
.idea/**/shelf

# Generated files
.idea/**/contentModel.xml

# Sensitive or high-churn files
.idea/**/dataSources/
.idea/**/dataSources.ids
.idea/**/dataSources.local.xml
.idea/**/sqlDataSources.xml
.idea/**/dynamic.xml
.idea/**/uiDesigner.xml
.idea/**/dbnavigator.xml

# Gradle
.idea/**/gradle.xml
.idea/**/libraries

# Gradle and Maven with auto-import
# When using Gradle or Maven with auto-import, you should exclude module files,
# since they will be recreated, and may cause churn.  Uncomment if using
# auto-import.
# .idea/modules.xml
# .idea/*.iml
# .idea/modules
# *.iml
# *.ipr

# CMake
cmake-build-*/

# Mongo Explorer plugin
.idea/**/mongoSettings.xml

# File-based project format
*.iws

# IntelliJ
out/

# mpeltonen/sbt-idea plugin
.idea_modules/

# JIRA plugin
atlassian-ide-plugin.xml

# Cursive Clojure plugin
.idea/replstate.xml

# Crashlytics plugin (for Android Studio and IntelliJ)
com_crashlytics_export_strings.xml
crashlytics.properties
crashlytics-build.properties
fabric.properties

# Editor-based Rest Client
.idea/httpRequests

# Android studio 3.1+ serialized cache file
.idea/caches/build_file_checksums.ser

### JetBrains+all Patch ###
# Ignores the whole .idea folder and all .iml files
# See https://github.com/joeblau/gitignore.io/issues/186 and https://github.com/joeblau/gitignore.io/issues/360

.idea/

# Reason: https://github.com/joeblau/gitignore.io/issues/186#issuecomment-249601023

*.iml
modules.xml
.idea/misc.xml
*.ipr

# Sonarlint plugin
.idea/sonarlint

### Rails ###
*.rbc
capybara-*.html
.rspec
/db/*.sqlite3
/db/*.sqlite3-journal
/public/system
/coverage/
/spec/tmp
rerun.txt
pickle-email-*.html

# Ignore all logfiles and tempfiles.
/log/*
/tmp/*
!/log/.keep
!/tmp/.keep

# TODO Comment out this rule if you are OK with secrets being uploaded to the repo
config/initializers/secret_token.rb
config/master.key

# Only include if you have production secrets in this file, which is no longer a Rails default
# config/secrets.yml

# dotenv
# TODO Comment out this rule if environment variables can be committed
.env

## Environment normalization:
/.bundle
/vendor/bundle

# these should all be checked in to normalize the environment:
# Gemfile.lock, .ruby-version, .ruby-gemset

# unless supporting rvm < 1.11.0 or doing something fancy, ignore this:
.rvmrc

# if using bower-rails ignore default bower_components path bower.json files
/vendor/assets/bower_components
*.bowerrc
bower.json

# Ignore pow environment settings
.powenv

# Ignore Byebug command history file.
.byebug_history

# Ignore node_modules
node_modules/

# Ignore precompiled javascript packs
/public/packs
/public/packs-test
/public/assets

# Ignore yarn files
/yarn-error.log
yarn-debug.log*
.yarn-integrity

# Ignore uploaded files in development
/storage/*
!/storage/.keep

### Ruby ###
*.gem
/.config
/InstalledFiles
/pkg/
/spec/reports/
/spec/examples.txt
/test/tmp/
/test/version_tmp/
/tmp/

# Used by dotenv library to load environment variables.
# .env

# Ignore Byebug command history file.

## Specific to RubyMotion:
.dat*
.repl_history
build/
*.bridgesupport
build-iPhoneOS/
build-iPhoneSimulator/

## Specific to RubyMotion (use of CocoaPods):
#
# We recommend against adding the Pods directory to your .gitignore. However
# you should judge for yourself, the pros and cons are mentioned at:
# https://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
# vendor/Pods/

## Documentation cache and generated files:
/.yardoc/
/_yardoc/
/doc/
/rdoc/

/.bundle/
/lib/bundler/man/

# for a library or gem, you might want to ignore these files since the code is
# intended to run in multiple environments; otherwise, check them in:
# Gemfile.lock
# .ruby-version
# .ruby-gemset

# unless supporting rvm < 1.11.0 or doing something fancy, ignore this:

# End of https://www.gitignore.io/api/git,ruby,rails,jetbrains+all

You should now have the following three files in your docker-ruby-on-rails directory.

  • .dockerignore
  • compose.yaml
  • Dockerfile

To learn more about the files, see the following:

Run the application

Inside the docker-ruby-on-rails directory, run the following command in a terminal.

$ docker compose up --build

Open a browser and view the application at http://localhost:3000. You should see a simple Ruby on Rails application.

In the terminal, press ctrl+c to stop the application.

Run the application in the background

You can run the application detached from the terminal by adding the -d option. Inside the docker-ruby-on-rails directory, run the following command in a terminal.

$ docker compose up --build -d

Open a browser and view the application at http://localhost:3000.

You should see a simple Ruby on Rails application.

In the terminal, run the following command to stop the application.

$ docker compose down

For more information about Compose commands, see the Compose CLI reference.

Summary

In this section, you learned how you can containerize and run your Ruby application using Docker.

Related information:

Next steps

In the next section, you'll learn how you can develop your application using containers.

Develop your application