Rails Docker DB with migrations

test.rb

#/config/environments/test.rb
require 'docker'

Rails.application.configure do

  config.after_initialize do
    logger.info "db:migrate"
    ActiveRecord::Migrator.migrate(Rails.root.join("db/migrate"), nil)
  end
  
  config.before_initialize do
    # set this to something other than 'postgres'
    DB_NAME='myProject'

    def try_psql(container)
      ret = container.exec(["psql", "-U", "postgres", "-c", "SELECT 1"], wait: 10, tty: true)
      raise 'No PSQL SELECT 1' unless ret[2] == 0
    end

    def retry_psql(container)
      tries ||= 10
      print "."
      try_psql(container)
    rescue Exception => e
     sleep 1
     retry unless (tries -= 1).zero?
    else
      puts " success (attempt #{11-tries}/10)"
      # just hold off for a couple of seconds as the docker init process brings the database up and down a few times at startup.
      sleep 2
    end

    if( ENV['DOCKER_DB'] )
      container = Docker::Container.create( 'Image' => 'postgres:latest', 'ExposedPorts' => { '5432/tcp' => {} },
      'HostConfig' => {
        'PortBindings' => {
         '5432/tcp' => [{}]
        }
      }, 'Env' => [ 'POSTGRES_DB=' + DB_NAME ]  )

      container.start

      at_exit do
        puts "destroying docker container: #{container.id}"
        container.delete(:force => true)
      end

      puts "started docker container: #{container.id}"
      print "waiting for database: "
      retry_psql container

      json = container.json
      pg_port = json['NetworkSettings']['Ports']["5432/tcp"][0]["HostPort"]

      ENV['DATABASE_URL'] = "postgresql://postgres@localhost:#{pg_port}/" + DB_NAME + "?pool=5"
    end
  end
  
  # Other things from test.rb
  config.cache_classes = true
  config.eager_load = false
  config.public_file_server.enabled = true
  config.public_file_server.headers = {
    'Cache-Control' => 'public, max-age=3600'
  }
  config.consider_all_requests_local       = true
  config.action_controller.perform_caching = false
  config.action_dispatch.show_exceptions = false
  config.action_controller.allow_forgery_protection = false
  config.action_mailer.perform_caching = false
  config.action_mailer.delivery_method = :test
  config.active_support.deprecation = :stderr
end