Chotto Matte

application.rb

require_relative "boot"

require "rails/all"

# Require the gems listed in Gemfile, including any gems
# you've limited to :test, :development, or :production.
Bundler.require(*Rails.groups)

module YourApp
  class Application < Rails::Application
    # Initialize configuration defaults for originally generated Rails version.
    config.load_defaults 6.1

    # Settings in config/environments/* take precedence over those specified here.
    # Application configuration should go into files in config/initializers
    # -- all .rb files in that directory are automatically loaded.

    config.after_initialize do
      p "killing #{ENV["HOGE_PID"]}..."
      Process.kill("TERM", ENV["HOGE_PID"].to_i)
    end
  end
end

chotto_matte.rb

if child_pid = fork
  ENV["HOGE_PID"] = child_pid.to_s
  puts "exec #{ARGV}"
  sleep 5 # slow start
  exec *ARGV
else
  require "rack"
  Rack::Server.start(
    app: ->(_env) { [503, { "Content-Type" => "text/plain" }, ["chotto matte"]] },
    Port: ENV.fetch("PORT", 3000),
  )
end

console

$ ruby chotto_matte.rb bundle exec rails server