human
Complete this python program:
def collect_master_lb(hosts):
assistant
#Here is the Python program you requested.

    """Get a valid load balancer from the user and append it to the list of
    hosts.
    Ensure user does not specify a system already used as a master/node as
    this is an invalid configuration.
    """
    message = "\nSetting    up    high-availability    masters    requires    a    load    balancing    solution.\nPlease    provide    the    FQDN    of    a    host    that    will    be    configured    as    a    proxy.    This\ncan    be    either    an    existing    load    balancer    configured    to    balance    all    masters    on\nport    8443    or    a    new    host    that    will    have    HAProxy    installed    on    it.\n\nIf    the    host    provided    is    not    yet    configured,    a    reference    HAProxy    load\nbalancer    will    be    installed.    It's    important    to    note    that    while    the    rest    of    the\nenvironment    will    be    fault-tolerant,    this    reference    load    balancer    will    not    be.\nIt    can    be    replaced    post-installation    with    a    load    balancer    with    the    same\nhostname.\n"
    click.echo(message)
    host_props = {}
    def validate_prompt_lb(hostname):
        hostname = validate_prompt_hostname(hostname)
        for host in hosts:
            if ((host.connect_to == hostname) and (host.is_master() or host.is_node())):
                raise click.BadParameter(('Cannot    re-use    "%s"    as    a    load    balancer,    please    specify    a    separate    host' % hostname))
        return hostname
    lb_hostname = click.prompt('Enter    hostname    or    IP    address', value_proc=validate_prompt_lb)
    if lb_hostname:
        host_props['connect_to'] = lb_hostname
        install_haproxy = click.confirm('Should    the    reference    HAProxy    load    balancer    be    installed    on    this    host?')
        host_props['preconfigured'] = (not install_haproxy)
        host_props['roles'] = ['master_lb']
        return Host(**host_props)
    else:
        return None