def docker_version(host=None, component='server'):
    """ Return the version of Docker [Server]

        :param host: host or IP of the machine Docker is running on
        :type host: str
        :param component: Docker component
        :type component: str
        :return: Docker version
        :rtype: str
    """

    if component.lower() == 'client':
        component = 'Client'
    else:
        component = 'Server'

    # sudo is required for non-coreOS installs
    command = 'sudo docker version -f {{.{}.Version}}'.format(component)

    if host is None:
        success, output = shakedown.run_command_on_master(command, None, None, False)
    else:
        success, output = shakedown.run_command_on_host(host, command, None, None, False)

    if success:
        return output
    else:
        return 'unknown'
Return the version of Docker [Server]

        :param host: host or IP of the machine Docker is running on
        :type host: str
        :param component: Docker component
        :type component: str
        :return: Docker version
        :rtype: str