Add an existing node/member to an existing load-balancer configuration.

    CLI Example:

    .. code-block:: bash

        salt-cloud -f attach_lb gce name=lb member=myinstance

def attach_lb(kwargs=None, call=None):
    '''
    Add an existing node/member to an existing load-balancer configuration.

    CLI Example:

    .. code-block:: bash

        salt-cloud -f attach_lb gce name=lb member=myinstance
    '''
    if call != 'function':
        raise SaltCloudSystemExit(
            'The attach_lb function must be called with -f or --function.'
        )

    if not kwargs or 'name' not in kwargs:
        log.error(
            'A load-balancer name must be specified.'
        )
        return False
    if 'member' not in kwargs:
        log.error(
            'A node name name must be specified.'
        )
        return False

    conn = get_conn()
    node = conn.ex_get_node(kwargs['member'])

    lb_conn = get_lb_conn(conn)
    lb = lb_conn.get_balancer(kwargs['name'])

    __utils__['cloud.fire_event'](
        'event',
        'attach load_balancer',
        'salt/cloud/loadbalancer/attaching',
        args=kwargs,
        sock_dir=__opts__['sock_dir'],
        transport=__opts__['transport']
    )

    result = lb_conn.balancer_attach_compute_node(lb, node)

    __utils__['cloud.fire_event'](
        'event',
        'attached load_balancer',
        'salt/cloud/loadbalancer/attached',
        args=kwargs,
        sock_dir=__opts__['sock_dir'],
        transport=__opts__['transport']
    )
    return _expand_item(result)