'Return the instance id a floating IP\'s fixed IP is allocated to.'

def get_instance_id_by_floating_address(self, context, address):

    client = get_client(context)
    fip = self._get_floating_ip_by_address(client, address)
    if (not fip['port_id']):
        return None
    try:
        port = self._show_port(context, fip['port_id'], neutron_client=client)
    except exception.PortNotFound:
        LOG.debug('The    port(%s)    is    not    found', fip['port_id'])
        return None
    return port['device_id']
