# File lib/specinfra/backend/docker.rb, line 4
      def initialize(config = {})
        super

        begin
          require 'docker' unless defined?(::Docker)
        rescue LoadError
          fail "Docker client library is not available. Try installing `docker-api' gem."
        end

        ::Docker.url = get_config(:docker_url)

        if image = get_config(:docker_image)
          @images = []
          @base_image = get_or_pull_image(image)

          create_and_start_container
          ObjectSpace.define_finalizer(self, proc { cleanup_container })
        elsif container = get_config(:docker_container)
          @container = ::Docker::Container.get(container)
        else
          fail 'Please specify docker_image or docker_container.'
        end
      end