1. Create and deploy a Ruby on Rails hello app

You will see a hello response at / and ok at /health before adding any services.

1. Download and run locally

Download the hello ZIP into a working directory, then open a terminal in that directory:

unzip rails-hello.zip
cd rails-hello
bundle install
bundle exec puma -b tcp://0.0.0.0:3000

Keep it running. In another terminal, curl -fsS http://localhost:3000/health should print ok. Open http://localhost:3000/ and confirm the hello message. Stop the server with Ctrl+C.

The app source is small enough to inspect in full:

`Gemfile`

source "https://rubygems.org"
ruby "~> 3.4.0"
gem "rails", "~> 8.0.0"
gem "puma", "~> 6.6"

`Procfile`

web: bundle exec puma -b tcp://0.0.0.0:$PORT

`config.ru`

require_relative "config/environment"
run Rails.application

`Rakefile`

require_relative "config/application"
Rails.application.load_tasks

`bin/rails`

#!/usr/bin/env ruby
APP_PATH = File.expand_path("../config/application", __dir__)
require "bundler/setup"
require "rails/commands"

`config/application.rb`

require "bundler/setup"
require "rails"
require "action_controller/railtie"
module HelloTutorial
 class Application < Rails::Application
  config.load_defaults 8.0
  config.api_only = true
  config.eager_load = ENV["RAILS_ENV"] == "production"
  config.hosts << ENV["PAAS_PUBLIC_HOST"] if ENV["PAAS_PUBLIC_HOST"]
  config.logger = ActiveSupport::Logger.new($stdout)
 end
end

`config/environment.rb`

require_relative "application"
Rails.application.initialize!

`config/routes.rb`

Rails.application.routes.draw do
 root "hello#index"
 get "/health", to: "hello#health"
end

`app/controllers/hello_controller.rb`

class HelloController < ActionController::API
 def index
  render plain: "Hello from Rails on d2o!\n"
 end
 def health
  render plain: "ok\n"
 end
end

Keep the supplied lockfiles in Git. The buildpack uses these manifests and its runtime version declaration to reproduce the app’s dependencies.

2. Create the Environment

Dashboard: open Project Examples → create Environment rails, type Development, branch main, release source Build, Automatic deployment on.

CLI:

paas envs create rails -o "$TUTORIAL_ORG" -p examples --type development --branch main --release-source build

Dashboard: inside rails choose Add Resource → Web Application. Name it notes-web, choose Framework Ruby on Rails, Repository The environment’s shared repository, Directory blank (repository root), and Process type web. Use Port 3000, Health Check Path /health, and one replica. Click Create Resource.

CLI:

paas apps create notes-web --framework rails --shared-source --start-command web --port 3000 --health-check-path /health -o "$TUTORIAL_ORG" -p examples -e rails

4. Set the Rails application secret

Generate a value locally with ruby -rsecurerandom -e 'puts SecureRandom.hex(64)'. In the dashboard, open the rails Environment’s Secrets page and add RAILS_SECRET_KEY_BASE with that value. Secret creation is currently dashboard-only, including when you follow the CLI path. Do not put the value in Git or a plain config variable.

Dashboard: on notes-web → Config, add SECRET_KEY_BASE, choose Link to secret, and select RAILS_SECRET_KEY_BASE.

CLI: after creating the secret in the dashboard:

paas config set --secret-ref RAILS_SECRET_KEY_BASE SECRET_KEY_BASE -a notes-web -o "$TUTORIAL_ORG" -p examples -e rails

The platform supplies the value at runtime. Local development can use a locally generated SECRET_KEY_BASE; the source never contains a deployment secret.

5. Commit and push

Initialize a repository in the unpacked hello directory:

git init -b main
git add .
git commit -m "Add hello application"

Dashboard path: open the Environment’s Git remote panel, copy its shared-repository remote command into this directory, then run its push command. This is the Environment remote, not a per-app remote. The dashboard supplies the correct host and authentication URL.

CLI path: omit -a when setting the shared remote:

paas git remote -o "$TUTORIAL_ORG" -p examples -e rails
git push d2o main
paas watch -a notes-web -o "$TUTORIAL_ORG" -p examples -e rails

6. Verify the deployed app

Dashboard: open notes-web → Deployments, wait for the successful build and running instance, then open its public URL. Append /health; it should display ok. CLI: paas ps and paas logs with -o "$TUTORIAL_ORG" -p examples -e rails and -a notes-web show the running process. Use the public URL displayed in the dashboard, or read the url field from paas apps info notes-web --json with the same Organization, Project, and Environment flags.

APP_URL=https://your-app-host
curl -fsS "$APP_URL/health"
curl -fsS "$APP_URL/"

Set APP_URL to your actual URL, with no trailing slash. If the build fails, see troubleshooting before continuing.

Next: Persist notes in PostgreSQL.

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