def create(cls, config_file=None, logical_volume = None, cfg = None, **params):
        """
        Create a new instance based on the specified configuration file or the specified
        configuration and the passed in parameters.
        
        If the config_file argument is not None, the configuration is read from there. 
        Otherwise, the cfg argument is used.
        
        The config file may include other config files with a #import reference. The included
        config files must reside in the same directory as the specified file. 
        
        The logical_volume argument, if supplied, will be used to get the current physical 
        volume ID and use that as an override of the value specified in the config file. This 
        may be useful for debugging purposes when you want to debug with a production config 
        file but a test Volume. 
        
        The dictionary argument may be used to override any EC2 configuration values in the 
        config file. 
        """
        if config_file:
            cfg = Config(path=config_file)
        if cfg.has_section('EC2'):
            # include any EC2 configuration values that aren't specified in params:
            for option in cfg.options('EC2'):
                if option not in params:
                    params[option] = cfg.get('EC2', option)
        getter = CommandLineGetter()
        getter.get(cls, params)
        region = params.get('region')
        ec2 = region.connect()
        cls.add_credentials(cfg, ec2.aws_access_key_id, ec2.aws_secret_access_key)
        ami = params.get('ami')
        kp = params.get('keypair')
        group = params.get('group')
        zone = params.get('zone')
        # deal with possibly passed in logical volume:
        if logical_volume != None:
           cfg.set('EBS', 'logical_volume_name', logical_volume.name) 
        cfg_fp = StringIO.StringIO()
        cfg.write(cfg_fp)
        # deal with the possibility that zone and/or keypair are strings read from the config file:
        if isinstance(zone, Zone):
            zone = zone.name
        if isinstance(kp, KeyPair):
            kp = kp.name
        reservation = ami.run(min_count=1,
                              max_count=params.get('quantity', 1),
                              key_name=kp,
                              security_groups=[group],
                              instance_type=params.get('instance_type'),
                              placement = zone,
                              user_data = cfg_fp.getvalue())
        l = []
        i = 0
        elastic_ip = params.get('elastic_ip')
        instances = reservation.instances
        if elastic_ip != None and instances.__len__() > 0:
            instance = instances[0]
            print 'Waiting for instance to start so we can set its elastic IP address...'
            # Sometimes we get a message from ec2 that says that the instance does not exist.
            # Hopefully the following delay will giv eec2 enough time to get to a stable state:
            time.sleep(5) 
            while instance.update() != 'running':
                time.sleep(1)
            instance.use_ip(elastic_ip)
            print 'set the elastic IP of the first instance to %s' % elastic_ip
        for instance in instances:
            s = cls()
            s.ec2 = ec2
            s.name = params.get('name') + '' if i==0 else str(i)
            s.description = params.get('description')
            s.region_name = region.name
            s.instance_id = instance.id
            if elastic_ip and i == 0:
                s.elastic_ip = elastic_ip
            s.put()
            l.append(s)
            i += 1
        return l