Boilerplate for a containerized plain Ruby application
4 min read
Recently I've been poking around automation in order to experiment and build software on destroyable environments, so that I won't mess up with my operating system host.
That's where virtualization and containerization can help: I want to stand on a fast and destroyable environment which can be re-launch as many times as I want.
In this Gist I share how to launch an Ubuntu environment on the host using a lightweight VM manager, called multipass.
Virtualization is not the focus of this post, as you can check the Gist for further details.
Throughout this post, I will present how to build a plain Ruby containerized application using just Docker and Makefile, such that the boilerplate can be reused everytime we want to create a new app.
Let's create the
Makefile, which can be a centralized entrypoint for the commands we want to run. It's a good practice to have a Makefile in every app.
console: docker run \ --rm \ -it \ -v $(pwd):/$(basename $(pwd)) \ -w /$(basename $(pwd)) \ ruby:2.7 \ bash
Makefile is composed by targets. Each target can run a specific task which in turn can be a single command or a set of commands. In our example, we are running the
docker run along with its options:
docker run: creates a new container based on an image
--rm: will remove the container on exit
-it: allows a pseudo-terminal to interact
-v $(pwd):/$(basename $(pwd)): mounts the current directory from host to container
-w /$(basename $(pwd)): sets up the default working dir on container
ruby:2.7: the image from which the container will run. Docker tries to find the image locally, otherwise downloads it from a Docker registry
bash: the command executed on the container. bash will request a pseudo-terminal to interact
We can test the target by running:
It will open the bash from the container.
Docker command options can be verbose quickly as we add more complexity to our application. As a means to make it easier to use Docker in development, we can declare our container specification in a single file that can be reused.
Docker comes with docker-compose to solve that problem.
version: '3.9' services: dev: image: ruby:2.7 container_name: my-application working_dir: /my-application volumes: - ./:/my-application
Now, we can change our Makefile to use the docker-compose command:
console: docker-compose run dev bash
And check it:
The above configuration does the same job as running
docker run with volume option, working dir, image and so on.
Intending to bootstrap our application with TDD, the first file we create is the test file, which runs a simple dummy test. It seems silly, but enough for the purpose of this boilerplate, being able to be enhanced at a later time.
As for Ruby, we're gonna use
require 'test/unit' class AppTest < Test::Unit::TestCase def test_dummy assert_equal 1, 1 end end
test/unit does not come with this standard Ruby, making us to include the gem separately.
source 'https://rubygems.org' gem 'test-unit'
Now we can run
make console, and then from inside the container, run the command to install the gem from Gemfile:
Ruby will place the gems by default on
We can't forget that everytime we run
make console, a new container will be created, losing all the gems we have installed. As the application grows, running
bundle install can be onerous.
Let's use a named volume to use the host as a "cache":
version: '3.9' services: dev: image: ruby:2.7 container_name: my-application working_dir: /my-application volumes: - ./:/my-application - rubygems:/usr/local/bundle volumes: rubygems:
By doing this way, Docker will use this named volume in host for the gems placed at
/usr/local/bundle from running containers.
Running the test
As for now we are able to run the test:
make console bundle ruby app_test.rb
Improving the test command
Instead of entering the console everytime to run the test, we can run it directly upon container creation:
docker-compose run dev ruby app_test.rb
The, improving our workflow is easy as follows:
console: docker-compose run dev bash utest: docker-compose run dev ruby app_test.rb
Entering the console to run stuff:
Running the test:
The purpose of this article was to share a way of creating the boilerplate for a containerized Ruby application, allowing us to experiment and play on destroyable environments, remaining our OS host untouchable.