#150 Rails 6 with Docker

All about running Rails 6 with Docker

Notes

Running Rails with Docker is a great solution for both development (eliminates any reliance on local system dependencies) and for deployment (no ruby or rails specific dependencies for operations to deal with).

These notes cover a few examples of running Rails 6 application in Docker, with solutions for some common Rails-specific refinements.

Running docker-compose-rails-6 example

The github.com/DiveIntoHacking/docker-compose-rails-6 repo is a simple pre-fab example. Runs just as advertized…

git clone git@github.com:DiveIntoHacking/docker-compose-rails-6.git
cd docker-compose-rails-6
docker-compose run --rm web bundle install
docker-compose run --rm web yarn install
docker-compose up
docker-compose exec web ./bin/rails db:create

And it is running OK on http://localhost:3000 ..

DiveIntoHacking_initial_local

Cleaning up..

$ docker-compose down
Removing docker-compose-rails-6_web_1 ... done
Removing docker-compose-rails-6_db_1  ... done
Removing network docker-compose-rails-6_default

A couple of things to note about this configuration:

the app folder is mapped to local file system
bundle and yarn installs assets in vender/bundle and node_modules i.e. these are not shipped in the image. This is not really ideal for deployment, as runtime dependencies could change from test and build-time.

Building a New Image From a Local Installation

Let’s start from scratch, with the basic aim of having a rails application that can:

run in the local OS as normal for development and testing
run in docker for development and testing

At the time of writing, I’m using Ruby 2.7.1 and Rails 6.0.3.3

Step 1: Build a Basic App (Local)

Checking Pre-requisites and Installation

$ node -v
v12.8.0
$ npm -v
6.10.2
$ ruby -v
ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-darwin17]
$ gem install rails -v 6.0.3.3
...
$ rails --version
Rails 6.0.3.3
$ docker --version
Docker version 19.03.12, build 48a66213fe

Out-of-the-box application generation, built locally and using a local PostgreSQL database:

rails new minime --database=postgresql
cd minime

The rails new takes care of dependency installation. To recreate or install elsewhere, install dependencies:

bundle install
yarn install

Create and migrate the database, then fire up the app…

$ rails db:create
The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
Created database 'minime_development'
Created database 'minime_test'

NB: get rid of the tzinfo-data platform warning with bundle config --local disable_platform_warnings true

$ rails db:migrate
$ rails server
=> Booting Puma
=> Rails 6.0.3.4 application starting in development
=> Run `rails server --help` for more startup options
Puma starting in single mode...
* Version 4.3.6 (ruby 2.7.1-p83), codename: Mysterious Traveller
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://127.0.0.1:3000
* Listening on tcp://[::1]:3000
* Listening on tcp://127.94.0.2:3000
* Listening on tcp://127.94.0.1:3000
Use Ctrl-C to stop

And it is running OK on http://localhost:3000 ..

web_initial_local

Adding a few more features (including tests)

rails generate controller Articles
rails generate model Article title:string text:text
rails db:migrate

And some tests:

$ rails test
Running via Spring preloader in process 57084
Run options: --seed 26227

# Running:

.

Finished in 0.439060s, 2.2776 runs/s, 2.2776 assertions/s.
1 runs, 1 assertions, 0 failures, 0 errors, 0 skips

Step 2: Adding Docker Support

Adding:

Dockerfile
docker-compose.yml
.dockerignore to prevent locally installed assets from being added to the image
entrypoint.sh provides a default Rails application startup for the

Commands:

docker-compose build
docker-compose run --rm web bundle exec rails db:create
docker-compose run --rm web bundle exec rails db:migrate
docker-compose up

Or to daemonize:

docker-compose up

And it is running OK on http://0.0.0.0:3000 ..

web_initial_dockerized

Run a shell:

docker-compose run --rm web bash

Run tests in docker:

$ docker-compose run --rm web bundle exec rails test
Starting minime_db_1 ... done
Running via Spring preloader in process 15
Run options: --seed 19759

# Running:

.

Finished in 9.117707s, 0.1097 runs/s, 0.1097 assertions/s.
1 runs, 1 assertions, 0 failures, 0 errors, 0 skips

For development, it can be useful to share the file system, so that editing locally can be immediately picked up by the container.

However, care is required with folders that may contain platform-specific versions. This is specifically an issue with node_modules.

The following volume mapping in the docker-compose.yml shares the application files but excludes node_modules.

web:
  volumes:
    - .:/app
    - /app/node_modules/

If file sharing is not required, this volumes section can be removed (speeds things up).

Testing the shared file system by running localhost:3000/articles from docker and modifying the view file on the local file system:

articles_mod

Environment-driven Database Configuration

Updating the config/database.yml to ensure that the database configuration can be completely driven from the environment (and the docker-compose.yml file).

default: &default
  adapter: postgresql
  encoding: unicode
  host: <%= ENV['RAILS_DB_HOST'] %>
  username: <%= ENV['RAILS_DB_USERNAME'] %>
  password: <%= ENV['RAILS_DB_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 } %>
  database: <%= ENV['RAILS_DB_NAME'] || "minime_#{ENV['RAILS_ENV'] || 'development'}" %>

NB: alternatively, use the standard DATABASE_URL environment settings, as described in the Rails guides.

Credits and References

Rails on Docker: Using Docker Compose with Your Ruby on Rails Apps
Dockerize and Deploy to AWS EC2
Create new Rails 6 project with Docker
Setting up Rails 6 with PostgreSQL & Webpack on Docker
docker-compose-rails-6 - example repository defines docker files(Dockerfile and docker-compose.yml) to create the image
How to use Bundler with Docker
Quick start: Compose and Rails
Add a volume to Docker, but exclude a sub-folder - stackoverflow

Project Notes