def client(self):
        """The original :class:`docker.Client` object. All docker operation
        calling will be forwarded here. ::

            docker.create_container('ubuntu')
            docker.client.create_container('ubuntu')  # equivalent
        """
        if not self.app.config['DOCKER_URL']:
            raise RuntimeError('"DOCKER_URL" must be specified')

        if not self.app.extensions['docker.client']:
            self.app.extensions['docker.client'] = Client(
                base_url=self.app.config['DOCKER_URL'],
                version=self.app.config['DOCKER_VERSION'],
                timeout=self.app.config['DOCKER_TIMEOUT'],
                tls=make_tls_config(self.app.config))
        return self.app.extensions['docker.client']