path: root/openstack/common/rpc/impl_zmq.py

# vim: tabstop=4 shiftwidth=4 softtabstop=4

#    Copyright 2011 Cloudscaling Group, Inc
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

import os
import pprint
import re
import socket
import sys
import types
import uuid

import eventlet
import greenlet
from oslo.config import cfg

from openstack.common import excutils
from openstack.common.gettextutils import _
from openstack.common import importutils
from openstack.common import jsonutils
from openstack.common.rpc import common as rpc_common

zmq = importutils.try_import('eventlet.green.zmq')

# for convenience, are not modified.
pformat = pprint.pformat
Timeout = eventlet.timeout.Timeout
LOG = rpc_common.LOG
RemoteError = rpc_common.RemoteError
RPCException = rpc_common.RPCException

zmq_opts = [
    cfg.StrOpt('rpc_zmq_bind_address', default='*',
               help='ZeroMQ bind address. Should be a wildcard (*), '
                    'an ethernet interface, or IP. '
                    'The "host" option should point or resolve to this '
                    'address.'),

    # The module.Class to use for matchmaking.
    cfg.StrOpt(
        'rpc_zmq_matchmaker',
        default=('openstack.common.rpc.'
                 'matchmaker.MatchMakerLocalhost'),
        help='MatchMaker driver',
    ),

    # The following port is unassigned by IANA as of 2012-05-21
    cfg.IntOpt('rpc_zmq_port', default=9501,
               help='ZeroMQ receiver listening port'),

    cfg.IntOpt('rpc_zmq_contexts', default=1,
               help='Number of ZeroMQ contexts, defaults to 1'),

    cfg.IntOpt('rpc_zmq_topic_backlog', default=None,
               help='Maximum number of ingress messages to locally buffer '
                    'per topic. Default is unlimited.'),

    cfg.StrOpt('rpc_zmq_ipc_dir', default='/var/run/openstack',
               help='Directory for holding IPC sockets'),

    cfg.StrOpt('rpc_zmq_host', default=socket.gethostname(),
               help='Name of this node. Must be a valid hostname, FQDN, or '
                    'IP address. Must match "host" option, if running Nova.')
]


CONF = cfg.CONF
CONF.register_opts(zmq_opts)

ZMQ_CTX = None  # ZeroMQ Context, must be global.
matchmaker = None  # memoized matchmaker object


def _serialize(data):
    """Serialization wrapper.

    We prefer using JSON, but it cannot encode all types.
    Error if a developer passes us bad data.
    """
    try:
        return jsonutils.dumps(data, ensure_ascii=True)
    except TypeError:
        with excutils.save_and_reraise_exception():
            LOG.error(_("JSON serialization failed."))


def _deserialize(data):
    """Deserialization wrapper."""
    LOG.debug(_("Deserializing: %s"), data)
    return jsonutils.loads(data)


class ZmqSocket(object):
    """A tiny wrapper around ZeroMQ.

    Simplifies the send/recv protocol and connection management.
    Can be used as a Context (supports the 'with' statement).
    """

    def __init__(self, addr, zmq_type, bind=True, subscribe=None):
        self.sock = _get_ctxt().socket(zmq_type)
        self.addr = addr
        self.type = zmq_type
        self.subscriptions = []

        # Support failures on sending/receiving on wrong socket type.
        self.can_recv = zmq_type in (zmq.PULL, zmq.SUB)
        self.can_send = zmq_type in (zmq.PUSH, zmq.PUB)
        self.can_sub = zmq_type in (zmq.SUB, )

        # Support list, str, & None for subscribe arg (cast to list)
        do_sub = {
            list: subscribe,
            str: [subscribe],
            type(None): []
        }[type(subscribe)]

        for f in do_sub:
            self.subscribe(f)

        str_data = {'addr': addr, 'type': self.socket_s(),
                    'subscribe': subscribe, 'bind': bind}

        LOG.debug(_("Connecting to %(addr)s with %(type)s"), str_data)
        LOG.debug(_("-> Subscribed to %(subscribe)s"), str_data)
        LOG.debug(_("-> bind: %(bind)s"), str_data)

        try:
            if bind:
                self.sock.bind(addr)
            else:
                self.sock.connect(addr)
        except Exception:
            raise RPCException(_("Could not open socket."))

    def socket_s(self):
        """Get socket type as string."""
        t_enum = ('PUSH', 'PULL', 'PUB', 'SUB', 'REP', 'REQ', 'ROUTER',
                  'DEALER')
        return dict(map(lambda t: (getattr(zmq, t), t), t_enum))[self.type]

    def subscribe(self, msg_filter):
        """Subscribe."""
        if not self.can_sub:
            raise RPCException("Cannot subscribe on this socket.")
        LOG.debug(_("Subscribing to %s"), msg_filter)

        try:
            self.sock.setsockopt(zmq.SUBSCRIBE, msg_filter)
        except Exception:
            return

        self.subscriptions.append(msg_filter)

    def unsubscribe(self, msg_filter):
        """Unsubscribe."""
        if msg_filter not in self.subscriptions:
            return
        self.sock.setsockopt(zmq.UNSUBSCRIBE, msg_filter)
        self.subscriptions.remove(msg_filter)

    def close(self):
        if self.sock is None or self.sock.closed:
            return

        # We must unsubscribe, or we'll leak descriptors.
        if self.subscriptions:
            for f in self.subscriptions:
                try:
                    self.sock.setsockopt(zmq.UNSUBSCRIBE, f)
                except Exception:
                    pass
            self.subscriptions = []

        try:
            # Default is to linger
            self.sock.close()
        except Exception:
            # While this is a bad thing to happen,
            # it would be much worse if some of the code calling this
            # were to fail. For now, lets log, and later evaluate
            # if we can safely raise here.
            LOG.error("ZeroMQ socket could not be closed.")
        self.sock = None

    def recv(self, **kwargs):
        if not self.can_recv:
            raise RPCException(_("You cannot recv on this socket."))
        return self.sock.recv_multipart(**kwargs)

    def send(self, data, **kwargs):
        if not self.can_send:
            raise RPCException(_("You cannot send on this socket."))
        self.sock.send_multipart(data, **kwargs)


class ZmqClient(object):
    """Client for ZMQ sockets."""

    def __init__(self, addr):
        self.outq = ZmqSocket(addr, zmq.PUSH, bind=False)

    def cast(self, msg_id, topic, data, envelope):
        msg_id = msg_id or 0

        if not envelope:
            self.outq.send(map(bytes,
                           (msg_id, topic, 'cast', _serialize(data))))
            return

        rpc_envelope = rpc_common.serialize_msg(data[1], envelope)
        zmq_msg = reduce(lambda x, y: x + y, rpc_envelope.items())
        self.outq.send(map(bytes,
                       (msg_id, topic, 'impl_zmq_v2', data[0]) + zmq_msg))

    def close(self):
        self.outq.close()


class RpcContext(rpc_common.CommonRpcContext):
    """Context that supports replying to a rpc.call."""
    def __init__(self, **kwargs):
        self.replies = []
        super(RpcContext, self).__init__(**kwargs)

    def deepcopy(self):
        values = self.to_dict()
        values['replies'] = self.replies
        return self.__class__(**values)

    def reply(self, reply=None, failure=None, ending=False):
        if ending:
            return
        self.replies.append(reply)

    @classmethod
    def marshal(self, ctx):
        ctx_data = ctx.to_dict()
        return _serialize(ctx_data)

    @classmethod
    def unmarshal(self, data):
        return RpcContext.from_dict(_deserialize(data))


class InternalContext(object):
    """Used by ConsumerBase as a private context for - methods."""

    def __init__(self, proxy):
        self.proxy = proxy
        self.msg_waiter = None

    def _get_response(self, ctx, proxy, topic, data):
        """Process a curried message and cast the result to topic."""
        LOG.debug(_("Running func with context: %s"), ctx.to_dict())
        data.setdefault('version', None)
        data.setdefault('args', {})

        try:
            result = proxy.dispatch(
                ctx, data['version'], data['method'],
                data.get('namespace'), **data['args'])
            return ConsumerBase.normalize_reply(result, ctx.replies)
        except greenlet.GreenletExit:
            # ignore these since they are just from shutdowns
            pass
        except rpc_common.ClientException as e:
            LOG.debug(_("Expected exception during message handling (%s)") %
                      e._exc_info[1])
            return {'exc':
                    rpc_common.serialize_remote_exception(e._exc_info,
                                                          log_failure=False)}
        except Exception:
            LOG.error(_("Exception during message handling"))
            return {'exc':
                    rpc_common.serialize_remote_exception(sys.exc_info())}

    def reply(self, ctx, proxy,
              msg_id=None, context=None, topic=None, msg=None):
        """Reply to a casted call."""
        # NOTE(ewindisch): context kwarg exists for Grizzly compat.
        #                  this may be able to be removed earlier than
        #                  'I' if ConsumerBase.process were refactored.
        if type(msg) is list:
            payload = msg[-1]
        else:
            payload = msg

        response = ConsumerBase.normalize_reply(
            self._get_response(ctx, proxy, topic, payload),
            ctx.replies)

        LOG.debug(_("Sending reply"))
        _multi_send(_cast, ctx, topic, {
            'method': '-process_reply',
            'args': {
                'msg_id': msg_id,  # Include for Folsom compat.
                'response': response
            }
        }, _msg_id=msg_id)


class ConsumerBase(object):
    """Base Consumer."""

    def __init__(self):
        self.private_ctx = InternalContext(None)

    @classmethod
    def normalize_reply(self, result, replies):
        #TODO(ewindisch): re-evaluate and document this method.
        if isinstance(result, types.GeneratorType):
            return list(result)
        elif replies:
            return replies
        else:
            return [result]

    def process(self, proxy, ctx, data):
        data.setdefault('version', None)
        data.setdefault('args', {})

        # Method starting with - are
        # processed internally. (non-valid method name)
        method = data.get('method')
        if not method:
            LOG.error(_("RPC message did not include method."))
            return

        # Internal method
        # uses internal context for safety.
        if method == '-reply':
            self.private_ctx.reply(ctx, proxy, **data['args'])
            return

        proxy.dispatch(ctx, data['version'],
                       data['method'], data.get('namespace'), **data['args'])


class ZmqBaseReactor(ConsumerBase):
    """A consumer class implementing a centralized casting broker (PULL-PUSH).

    Used for RoundRobin requests.
    """

    def __init__(self, conf):
        super(ZmqBaseReactor, self).__init__()

        self.proxies = {}
        self.threads = []
        self.sockets = []
        self.subscribe = {}

        self.pool = eventlet.greenpool.GreenPool(conf.rpc_thread_pool_size)

    def register(self, proxy, in_addr, zmq_type_in,
                 in_bind=True, subscribe=None):

        LOG.info(_("Registering reactor"))

        if zmq_type_in not in (zmq.PULL, zmq.SUB):
            raise RPCException("Bad input socktype")

        # Items push in.
        inq = ZmqSocket(in_addr, zmq_type_in, bind=in_bind,
                        subscribe=subscribe)

        self.proxies[inq] = proxy
        self.sockets.append(inq)

        LOG.info(_("In reactor registered"))

    def consume_in_thread(self):
        def _consume(sock):
            LOG.info(_("Consuming socket"))
            while True:
                self.consume(sock)

        for k in self.proxies.keys():
            self.threads.append(
                self.pool.spawn(_consume, k)
            )

    def wait(self):
        for t in self.threads:
            t.wait()

    def close(self):
        for s in self.sockets:
            s.close()

        for t in self.threads:
            t.kill()


class ZmqProxy(ZmqBaseReactor):
    """A consumer class implementing a topic-based proxy.

    Forwards to IPC sockets.
    """

    def __init__(self, conf):
        super(ZmqProxy, self).__init__(conf)
        pathsep = set((os.path.sep or '', os.path.altsep or '', '/', '\\'))
        self.badchars = re.compile(r'[%s]' % re.escape(''.join(pathsep)))

        self.topic_proxy = {}

    def consume(self, sock):
        ipc_dir = CONF.rpc_zmq_ipc_dir

        data = sock.recv(copy=False)
        topic = data[1].bytes

        if topic.startswith('fanout~'):
            sock_type = zmq.PUB
            topic = topic.split('.', 1)[0]
        elif topic.startswith('zmq_replies'):
            sock_type = zmq.PUB
        else:
            sock_type = zmq.PUSH

        if topic not in self.topic_proxy:
            def publisher(waiter):
                LOG.info(_("Creating proxy for topic: %s"), topic)

                try:
                    # The topic is received over the network,
                    # don't trust this input.
                    if self.badchars.search(topic) is not None:
                        emsg = _("Topic contained dangerous characters.")
                        LOG.warn(emsg)
                        raise RPCException(emsg)

                    out_sock = ZmqSocket("ipc://%s/zmq_topic_%s" %
                                         (ipc_dir, topic),
                                         sock_type, bind=True)
                except RPCException:
                    waiter.send_exception(*sys.exc_info())
                    return

                self.topic_proxy[topic] = eventlet.queue.LightQueue(
                    CONF.rpc_zmq_topic_backlog)
                self.sockets.append(out_sock)

                # It takes some time for a pub socket to open,
                # before we can have any faith in doing a send() to it.
                if sock_type == zmq.PUB:
                    eventlet.sleep(.5)

                waiter.send(True)

                while(True):
                    data = self.topic_proxy[topic].get()
                    out_sock.send(data, copy=False)

            wait_sock_creation = eventlet.event.Event()
            eventlet.spawn(publisher, wait_sock_creation)

            try:
                wait_sock_creation.wait()
            except RPCException:
                LOG.error(_("Topic socket file creation failed."))
                return

        try:
            self.topic_proxy[topic].put_nowait(data)
        except eventlet.queue.Full:
            LOG.error(_("Local per-topic backlog buffer full for topic "
                        "%(topic)s. Dropping message.") % {'topic': topic})

    def consume_in_thread(self):
        """Runs the ZmqProxy service."""
        ipc_dir = CONF.rpc_zmq_ipc_dir
        consume_in = "tcp://%s:%s" % \
            (CONF.rpc_zmq_bind_address,
             CONF.rpc_zmq_port)
        consumption_proxy = InternalContext(None)

        try:
            os.makedirs(ipc_dir)
        except os.error:
            if not os.path.isdir(ipc_dir):
                with excutils.save_and_reraise_exception():
                    LOG.error(_("Required IPC directory does not exist at"
                                " %s") % (ipc_dir, ))
        try:
            self.register(consumption_proxy,
                          consume_in,
                          zmq.PULL)
        except zmq.ZMQError:
            if os.access(ipc_dir, os.X_OK):
                with excutils.save_and_reraise_exception():
                    LOG.error(_("Permission denied to IPC directory at"
                                " %s") % (ipc_dir, ))
            with excutils.save_and_reraise_exception():
                LOG.error(_("Could not create ZeroMQ receiver daemon. "
                            "Socket may already be in use."))

        super(ZmqProxy, self).consume_in_thread()


def unflatten_envelope(packenv):
    """Unflattens the RPC envelope.

    Takes a list and returns a dictionary.
    i.e. [1,2,3,4] => {1: 2, 3: 4}
    """
    i = iter(packenv)
    h = {}
    try:
        while True:
            k = i.next()
            h[k] = i.next()
    except StopIteration:
        return h


class ZmqReactor(ZmqBaseReactor):
    """A consumer class implementing a consumer for messages.

    Can also be used as a 1:1 proxy
    """

    def __init__(self, conf):
        super(ZmqReactor, self).__init__(conf)

    def consume(self, sock):
        #TODO(ewindisch): use zero-copy (i.e. references, not copying)
        data = sock.recv()
        LOG.debug(_("CONSUMER RECEIVED DATA: %s"), data)

        proxy = self.proxies[sock]

        if data[2] == 'cast':  # Legacy protocol
            packenv = data[3]

            ctx, msg = _deserialize(packenv)
            request = rpc_common.deserialize_msg(msg)
            ctx = RpcContext.unmarshal(ctx)
        elif data[2] == 'impl_zmq_v2':
            packenv = data[4:]

            msg = unflatten_envelope(packenv)
            request = rpc_common.deserialize_msg(msg)

            # Unmarshal only after verifying the message.
            ctx = RpcContext.unmarshal(data[3])
        else:
            LOG.error(_("ZMQ Envelope version unsupported or unknown."))
            return

        self.pool.spawn_n(self.process, proxy, ctx, request)


class Connection(rpc_common.Connection):
    """Manages connections and threads."""

    def __init__(self, conf):
        self.topics = []
        self.reactor = ZmqReactor(conf)

    def create_consumer(self, topic, proxy, fanout=False):
        # Register with matchmaker.
        _get_matchmaker().register(topic, CONF.rpc_zmq_host)

        # Subscription scenarios
        if fanout:
            sock_type = zmq.SUB
            subscribe = ('', fanout)[type(fanout) == str]
            topic = 'fanout~' + topic.split('.', 1)[0]
        else:
            sock_type = zmq.PULL
            subscribe = None
            topic = '.'.join((topic.split('.', 1)[0], CONF.rpc_zmq_host))

        if topic in self.topics:
            LOG.info(_("Skipping topic registration. Already registered."))
            return

        # Receive messages from (local) proxy
        inaddr = "ipc://%s/zmq_topic_%s" % \
            (CONF.rpc_zmq_ipc_dir, topic)

        LOG.debug(_("Consumer is a zmq.%s"),
                  ['PULL', 'SUB'][sock_type == zmq.SUB])

        self.reactor.register(proxy, inaddr, sock_type,
                              subscribe=subscribe, in_bind=False)
        self.topics.append(topic)

    def close(self):
        _get_matchmaker().stop_heartbeat()
        for topic in self.topics:
            _get_matchmaker().unregister(topic, CONF.rpc_zmq_host)

        self.reactor.close()
        self.topics = []

    def wait(self):
        self.reactor.wait()

    def consume_in_thread(self):
        _get_matchmaker().start_heartbeat()
        self.reactor.consume_in_thread()


def _cast(addr, context, topic, msg, timeout=None, envelope=False,
          _msg_id=None):
    timeout_cast = timeout or CONF.rpc_cast_timeout
    payload = [RpcContext.marshal(context), msg]

    with Timeout(timeout_cast, exception=rpc_common.Timeout):
        try:
            conn = ZmqClient(addr)

            # assumes cast can't return an exception
            conn.cast(_msg_id, topic, payload, envelope)
        except zmq.ZMQError:
            raise RPCException("Cast failed. ZMQ Socket Exception")
        finally:
            if 'conn' in vars():
                conn.close()


def _call(addr, context, topic, msg, timeout=None,
          envelope=False):
    # timeout_response is how long we wait for a response
    timeout = timeout or CONF.rpc_response_timeout

    # The msg_id is used to track replies.
    msg_id = uuid.uuid4().hex

    # Replies always come into the reply service.
    reply_topic = "zmq_replies.%s" % CONF.rpc_zmq_host

    LOG.debug(_("Creating payload"))
    # Curry the original request into a reply method.
    mcontext = RpcContext.marshal(context)
    payload = {
        'method': '-reply',
        'args': {
            'msg_id': msg_id,
            'topic': reply_topic,
            # TODO(ewindisch): safe to remove mcontext in I.
            'msg': [mcontext, msg]
        }
    }

    LOG.debug(_("Creating queue socket for reply waiter"))

    # Messages arriving async.
    # TODO(ewindisch): have reply consumer with dynamic subscription mgmt
    with Timeout(timeout, exception=rpc_common.Timeout):
        try:
            msg_waiter = ZmqSocket(
                "ipc://%s/zmq_topic_zmq_replies.%s" %
                (CONF.rpc_zmq_ipc_dir,
                 CONF.rpc_zmq_host),
                zmq.SUB, subscribe=msg_id, bind=False
            )

            LOG.debug(_("Sending cast"))
            _cast(addr, context, topic, payload, envelope)

            LOG.debug(_("Cast sent; Waiting reply"))
            # Blocks until receives reply
            msg = msg_waiter.recv()
            LOG.debug(_("Received message: %s"), msg)
            LOG.debug(_("Unpacking response"))

            if msg[2] == 'cast':  # Legacy version
                raw_msg = _deserialize(msg[-1])[-1]
            elif msg[2] == 'impl_zmq_v2':
                rpc_envelope = unflatten_envelope(msg[4:])
                raw_msg = rpc_common.deserialize_msg(rpc_envelope)
            else:
                raise rpc_common.UnsupportedRpcEnvelopeVersion(
                    _("Unsupported or unknown ZMQ envelope returned."))

            responses = raw_msg['args']['response']
        # ZMQError trumps the Timeout error.
        except zmq.ZMQError:
            raise RPCException("ZMQ Socket Error")
        except (IndexError, KeyError):
            raise RPCException(_("RPC Message Invalid."))
        finally:
            if 'msg_waiter' in vars():
                msg_waiter.close()

    # It seems we don't need to do all of the following,
    # but perhaps it would be useful for multicall?
    # One effect of this is that we're checking all
    # responses for Exceptions.
    for resp in responses:
        if isinstance(resp, types.DictType) and 'exc' in resp:
            raise rpc_common.deserialize_remote_exception(CONF, resp['exc'])

    return responses[-1]


def _multi_send(method, context, topic, msg, timeout=None,
                envelope=False, _msg_id=None):
    """Wraps the sending of messages.

    Dispatches to the matchmaker and sends message to all relevant hosts.
    """
    conf = CONF
    LOG.debug(_("%(msg)s") % {'msg': ' '.join(map(pformat, (topic, msg)))})

    queues = _get_matchmaker().queues(topic)
    LOG.debug(_("Sending message(s) to: %s"), queues)

    # Don't stack if we have no matchmaker results
    if not queues:
        LOG.warn(_("No matchmaker results. Not casting."))
        # While not strictly a timeout, callers know how to handle
        # this exception and a timeout isn't too big a lie.
        raise rpc_common.Timeout(_("No match from matchmaker."))

    # This supports brokerless fanout (addresses > 1)
    for queue in queues:
        (_topic, ip_addr) = queue
        _addr = "tcp://%s:%s" % (ip_addr, conf.rpc_zmq_port)

        if method.__name__ == '_cast':
            eventlet.spawn_n(method, _addr, context,
                             _topic, msg, timeout, envelope,
                             _msg_id)
            return
        return method(_addr, context, _topic, msg, timeout,
                      envelope)


def create_connection(conf, new=True):
    return Connection(conf)


def multicall(conf, *args, **kwargs):
    """Multiple calls."""
    return _multi_send(_call, *args, **kwargs)


def call(conf, *args, **kwargs):
    """Send a message, expect a response."""
    data = _multi_send(_call, *args, **kwargs)
    return data[-1]


def cast(conf, *args, **kwargs):
    """Send a message expecting no reply."""
    _multi_send(_cast, *args, **kwargs)


def fanout_cast(conf, context, topic, msg, **kwargs):
    """Send a message to all listening and expect no reply."""
    # NOTE(ewindisch): fanout~ is used because it avoid splitting on .
    # and acts as a non-subtle hint to the matchmaker and ZmqProxy.
    _multi_send(_cast, context, 'fanout~' + str(topic), msg, **kwargs)


def notify(conf, context, topic, msg, envelope):
    """Send notification event.

    Notifications are sent to topic-priority.
    This differs from the AMQP drivers which send to topic.priority.
    """
    # NOTE(ewindisch): dot-priority in rpc notifier does not
    # work with our assumptions.
    topic = topic.replace('.', '-')
    cast(conf, context, topic, msg, envelope=envelope)


def cleanup():
    """Clean up resources in use by implementation."""
    global ZMQ_CTX
    if ZMQ_CTX:
        ZMQ_CTX.term()
    ZMQ_CTX = None

    global matchmaker
    matchmaker = None


def _get_ctxt():
    if not zmq:
        raise ImportError("Failed to import eventlet.green.zmq")

    global ZMQ_CTX
    if not ZMQ_CTX:
        ZMQ_CTX = zmq.Context(CONF.rpc_zmq_contexts)
    return ZMQ_CTX


def _get_matchmaker(*args, **kwargs):
    global matchmaker
    if not matchmaker:
        mm = CONF.rpc_zmq_matchmaker
        if mm.endswith('matchmaker.MatchMakerRing'):
            mm.replace('matchmaker', 'matchmaker_ring')
            LOG.warn(_('rpc_zmq_matchmaker = %(orig)s is deprecated; use'
                       ' %(new)s instead') % dict(
                     orig=CONF.rpc_zmq_matchmaker, new=mm))
        matchmaker = importutils.import_object(mm, *args, **kwargs)
    return matchmaker