def set_availability_zone(radl, zone):
    """
    Modify RADL to set availability zone
    """
    radl_new = ''

    for line in radl.split('\n'):
        if line.startswith('system'):
            line = line + "\navailability_zone = '%s' and" % zone
        radl_new = radl_new + line + '\n'

    return radl_new