A small collection of scripts and routines to help ruby development within containers

gem install on_container -v 0.0.12



Welcome to your new gem! In this directory, you'll find the files you need to be able to package up your Ruby library into a gem. Put your Ruby code in the file lib/on_container. To experiment with that code, run bin/console for an interactive prompt.

TODO: Delete this and the text above, and describe your gem


Add this line to your application's Gemfile:

gem 'on_container'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install on_container


Development Routines & Docker Entrypoint Scripts

We use some routines included in this gem to create compelling development entrypoint scripts for docker development containers.

In this example, we'll be using the on_container/dev/rails routine bundle to create our dev entrypoint:

#!/usr/bin/env ruby

# frozen_string_literal: true

require 'on_container/dev/rails'


# `on_setup_lock_acquired` prevents multiple app containers from running
# the setup process concurrently:
on_setup_lock_acquired do

  wait_for_service_to_accept_connections 'tcp://postgres:5432'
  setup_activerecord_database unless activerecord_database_ready?

  remove_rails_pidfile if rails_server?
end if command_requires_setup?


Loading secrets into environment variables

When using Docker Swarm, the secrets are loaded as files mounted into the container's filesystem.

The on_container/load_env_secrets runs a couple of routines that reads these files into environment variables.

For our Rails example app, we added the following line to the config/boot.rb file:

# frozen_string_literal: true

ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../Gemfile', __dir__)

require 'bundler/setup' # Set up gems listed in the Gemfile.
require 'bootsnap/setup' # Speed up boot time by caching expensive operations.

# Load swarm/gcp secrets to ENV:
require 'on_container/load_env_secrets'

Loading Google Cloud Secret Manager secrets into ENV

If you require loading YAML data stored at Google Cloud Secret Manager, you will require the following steps:

  1. Install the google-cloud-secret_manager gem

On your gemfile:

# Read secrets from Google Cloud Secret Manager
gem 'google-cloud-secret_manager', '~> 1.0'
  1. Require it at config/boot.rb

On config/boot, right before requiring on_container/load_env_secrets:

# Require Google Cloud Secret Manager to enable 'on_container/load_env_secrets'
# loading secrets from GCP to ENV:
require 'google/cloud/secret_manager'

# Load swarm/gcp secrets to ENV:
require 'on_container/load_env_secrets'
  1. Make sure your app has google cloud credentials configured, and have access to the secrets your'e planning to use.

  2. Configure any number of environment variables ending with _GOOGLE_CLOUD_SECRET, each containing the secret you want to load. In the following example, the command to deploy an image into Google Cloud Run:

gcloud run deploy my-demo-app \
  --platform "managed" \
  --region us-central1 \
  --allow-unauthenticated \
  --set-env-vars A_GOOGLE_CLOUD_SECRET=my-super-secret \
  --set-env-vars ANOTHER_GOOGLE_CLOUD_SECRET=project/another-project/secrets/another-secret/versions/1 \
  --service-account=my-demo-service-account@google-cloud \
  --image gcr.io/my-demo-project/my-demo-app:latest

Inserting credentials into URL environment variables

The on_container/load_env_secrets also merges any credential available in environment variables into any matching _URL environment variable. For example, consider the following environment variables:


The routine will merge DATABASE_USER and DATABASE_PASS into DATABASE_URL:

> postgres://postgres:3x4mpl3P455w0rd@postgres:5432/?encoding=unicode


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.


Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/on_container. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.


The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the OnContainer project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.