Rename AbstractCoordinator -> BaseCoordinator, log as kafka.coordinator

1 files changed, 677 insertions, 0 deletions

diff --git a/kafka/coordinator/base.py b/kafka/coordinator/base.py
new file mode 100644
index 0000000..4f16bb0
--- /dev/null
+++ b/kafka/coordinator/base.py
@@ -0,0 +1,677 @@
+import abc
+import copy
+import logging
+import time
+
+import six
+
+import kafka.common as Errors
+from kafka.future import Future
+from kafka.protocol.commit import (GroupCoordinatorRequest,
+                                   OffsetCommitRequest_v2 as OffsetCommitRequest)
+from kafka.protocol.group import (HeartbeatRequest, JoinGroupRequest,
+                                  LeaveGroupRequest, SyncGroupRequest)
+from .heartbeat import Heartbeat
+
+log = logging.getLogger('kafka.coordinator')
+
+
+class BaseCoordinator(object):
+    """
+    BaseCoordinator implements group management for a single group member
+    by interacting with a designated Kafka broker (the coordinator). Group
+    semantics are provided by extending this class.  See ConsumerCoordinator
+    for example usage.
+
+    From a high level, Kafka's group management protocol consists of the
+    following sequence of actions:
+
+    1. Group Registration: Group members register with the coordinator providing
+       their own metadata (such as the set of topics they are interested in).
+
+    2. Group/Leader Selection: The coordinator select the members of the group
+       and chooses one member as the leader.
+
+    3. State Assignment: The leader collects the metadata from all the members
+       of the group and assigns state.
+
+    4. Group Stabilization: Each member receives the state assigned by the
+       leader and begins processing.
+
+    To leverage this protocol, an implementation must define the format of
+    metadata provided by each member for group registration in group_protocols()
+    and the format of the state assignment provided by the leader in
+    _perform_assignment() and which becomes available to members in
+    _on_join_complete().
+    """
+
+    DEFAULT_CONFIG = {
+        'group_id': 'kafka-python-default-group',
+        'session_timeout_ms': 30000,
+        'heartbeat_interval_ms': 3000,
+        'retry_backoff_ms': 100,
+    }
+
+    def __init__(self, client, **configs):
+        """
+        Keyword Arguments:
+            group_id (str): name of the consumer group to join for dynamic
+                partition assignment (if enabled), and to use for fetching and
+                committing offsets. Default: 'kafka-python-default-group'
+            session_timeout_ms (int): The timeout used to detect failures when
+                using Kafka's group managementment facilities. Default: 30000
+            heartbeat_interval_ms (int): The expected time in milliseconds
+                between heartbeats to the consumer coordinator when using
+                Kafka's group management feature. Heartbeats are used to ensure
+                that the consumer's session stays active and to facilitate
+                rebalancing when new consumers join or leave the group. The
+                value must be set lower than session_timeout_ms, but typically
+                should be set no higher than 1/3 of that value. It can be
+                adjusted even lower to control the expected time for normal
+                rebalances. Default: 3000
+            retry_backoff_ms (int): Milliseconds to backoff when retrying on
+                errors. Default: 100.
+        """
+        self.config = copy.copy(self.DEFAULT_CONFIG)
+        for key in self.config:
+            if key in configs:
+                self.config[key] = configs[key]
+
+        self._client = client
+        self.generation = OffsetCommitRequest.DEFAULT_GENERATION_ID
+        self.member_id = JoinGroupRequest.UNKNOWN_MEMBER_ID
+        self.group_id = self.config['group_id']
+        self.coordinator_id = None
+        self.rejoin_needed = True
+        self.needs_join_prepare = True
+        self.heartbeat = Heartbeat(**self.config)
+        self.heartbeat_task = HeartbeatTask(self)
+        #self.sensors = GroupCoordinatorMetrics(metrics, metric_group_prefix, metric_tags)
+
+    @abc.abstractmethod
+    def protocol_type(self):
+        """
+        Unique identifier for the class of protocols implements
+        (e.g. "consumer" or "connect").
+
+        Returns:
+            str: protocol type name
+        """
+        pass
+
+    @abc.abstractmethod
+    def group_protocols(self):
+        """Return the list of supported group protocols and metadata.
+
+        This list is submitted by each group member via a JoinGroupRequest.
+        The order of the protocols in the list indicates the preference of the
+        protocol (the first entry is the most preferred). The coordinator takes
+        this preference into account when selecting the generation protocol
+        (generally more preferred protocols will be selected as long as all
+        members support them and there is no disagreement on the preference).
+
+        Note: metadata must be type bytes or support an encode() method
+
+        Returns:
+            list: [(protocol, metadata), ...]
+        """
+        pass
+
+    @abc.abstractmethod
+    def _on_join_prepare(self, generation, member_id):
+        """Invoked prior to each group join or rejoin.
+
+        This is typically used to perform any cleanup from the previous
+        generation (such as committing offsets for the consumer)
+
+        Arguments:
+            generation (int): The previous generation or -1 if there was none
+            member_id (str): The identifier of this member in the previous group
+                or '' if there was none
+        """
+        pass
+
+    @abc.abstractmethod
+    def _perform_assignment(self, leader_id, protocol, members):
+        """Perform assignment for the group.
+
+        This is used by the leader to push state to all the members of the group
+        (e.g. to push partition assignments in the case of the new consumer)
+
+        Arguments:
+            leader_id (str): The id of the leader (which is this member)
+            protocol (str): the chosen group protocol (assignment strategy)
+            members (list): [(member_id, metadata_bytes)] from
+                JoinGroupResponse. metadata_bytes are associated with the chosen
+                group protocol, and the Coordinator subclass is responsible for
+                decoding metadata_bytes based on that protocol.
+
+        Returns:
+            dict: {member_id: assignment}; assignment must either be bytes
+                or have an encode() method to convert to bytes
+        """
+        pass
+
+    @abc.abstractmethod
+    def _on_join_complete(self, generation, member_id, protocol,
+                          member_assignment_bytes):
+        """Invoked when a group member has successfully joined a group.
+
+        Arguments:
+            generation (int): the generation that was joined
+            member_id (str): the identifier for the local member in the group
+            protocol (str): the protocol selected by the coordinator
+            member_assignment_bytes (bytes): the protocol-encoded assignment
+                propagated from the group leader. The Coordinator instance is
+                responsible for decoding based on the chosen protocol.
+        """
+        pass
+
+    def coordinator_unknown(self):
+        """Check if we know who the coordinator is and have an active connection
+
+        Side-effect: reset coordinator_id to None if connection failed
+
+        Returns:
+            bool: True if the coordinator is unknown
+        """
+        if self.coordinator_id is None:
+            return True
+
+        if self._client.is_disconnected(self.coordinator_id):
+            self.coordinator_dead()
+            return True
+
+        return not self._client.ready(self.coordinator_id)
+
+    def ensure_coordinator_known(self):
+        """Block until the coordinator for this group is known
+        (and we have an active connection -- java client uses unsent queue).
+        """
+        while self.coordinator_unknown():
+
+            # Dont look for a new coordinator node if we are just waiting
+            # for connection to finish
+            if self.coordinator_id is not None:
+                self._client.poll()
+                continue
+
+            future = self._send_group_metadata_request()
+            self._client.poll(future=future)
+
+            if future.failed():
+                if future.retriable():
+                    metadata_update = self._client.cluster.request_update()
+                    self._client.poll(future=metadata_update)
+                else:
+                    raise future.exception # pylint: disable-msg=raising-bad-type
+
+    def need_rejoin(self):
+        """Check whether the group should be rejoined (e.g. if metadata changes)
+
+        Returns:
+            bool: True if it should, False otherwise
+        """
+        return self.rejoin_needed
+
+    def ensure_active_group(self):
+        """Ensure that the group is active (i.e. joined and synced)"""
+        if not self.need_rejoin():
+            return
+
+        if self.needs_join_prepare:
+            self._on_join_prepare(self.generation, self.member_id)
+            self.needs_join_prepare = False
+
+        while self.need_rejoin():
+            self.ensure_coordinator_known()
+
+            future = self._perform_group_join()
+            self._client.poll(future=future)
+
+            if future.succeeded():
+                member_assignment_bytes = future.value
+                self._on_join_complete(self.generation, self.member_id,
+                                       self.protocol, member_assignment_bytes)
+                self.needs_join_prepare = True
+                self.heartbeat_task.reset()
+            else:
+                exception = future.exception
+                if isinstance(exception, (Errors.UnknownMemberIdError,
+                                          Errors.RebalanceInProgressError,
+                                          Errors.IllegalGenerationError)):
+                    continue
+                elif not future.retriable():
+                    raise exception # pylint: disable-msg=raising-bad-type
+                time.sleep(self.config['retry_backoff_ms'] / 1000.0)
+
+    def _perform_group_join(self):
+        """Join the group and return the assignment for the next generation.
+
+        This function handles both JoinGroup and SyncGroup, delegating to
+        _perform_assignment() if elected leader by the coordinator.
+
+        Returns:
+            Future: resolves to the encoded-bytes assignment returned from the
+                group leader
+        """
+        if self.coordinator_unknown():
+            e = Errors.GroupCoordinatorNotAvailableError(self.coordinator_id)
+            return Future().failure(e)
+
+        # send a join group request to the coordinator
+        log.debug("(Re-)joining group %s", self.group_id)
+        request = JoinGroupRequest(
+            self.group_id,
+            self.config['session_timeout_ms'],
+            self.member_id,
+            self.protocol_type(),
+            [(protocol,
+              metadata if isinstance(metadata, bytes) else metadata.encode())
+             for protocol, metadata in self.group_protocols()])
+
+        # create the request for the coordinator
+        log.debug("Issuing request (%s) to coordinator %s", request, self.coordinator_id)
+        future = Future()
+        _f = self._client.send(self.coordinator_id, request)
+        _f.add_callback(self._handle_join_group_response, future)
+        _f.add_errback(self._failed_request, self.coordinator_id,
+                       request, future)
+        return future
+
+    def _failed_request(self, node_id, request, future, error):
+        log.error('Error sending %s to node %s [%s] -- marking coordinator dead',
+                  request.__class__.__name__, node_id, error)
+        self.coordinator_dead()
+        future.failure(error)
+
+    def _handle_join_group_response(self, future, response):
+        error_type = Errors.for_code(response.error_code)
+        if error_type is Errors.NoError:
+            self.member_id = response.member_id
+            self.generation = response.generation_id
+            self.rejoin_needed = False
+            self.protocol = response.group_protocol
+            log.info("Joined group '%s' (generation %s) with member_id %s",
+                     self.group_id, self.generation, self.member_id)
+            #self.sensors.join_latency.record(response.requestLatencyMs())
+            if response.leader_id == response.member_id:
+                log.info("Elected group leader -- performing partition"
+                         " assignments using %s", self.protocol)
+                self._on_join_leader(response).chain(future)
+            else:
+                self._on_join_follower().chain(future)
+
+        elif error_type is Errors.GroupLoadInProgressError:
+            log.debug("Attempt to join group %s rejected since coordinator is"
+                      " loading the group.", self.group_id)
+            # backoff and retry
+            future.failure(error_type(response))
+        elif error_type is Errors.UnknownMemberIdError:
+            # reset the member id and retry immediately
+            error = error_type(self.member_id)
+            self.member_id = JoinGroupRequest.UNKNOWN_MEMBER_ID
+            log.info("Attempt to join group %s failed due to unknown member id,"
+                     " resetting and retrying.", self.group_id)
+            future.failure(error)
+        elif error_type in (Errors.GroupCoordinatorNotAvailableError,
+                            Errors.NotCoordinatorForGroupError):
+            # re-discover the coordinator and retry with backoff
+            self.coordinator_dead()
+            log.info("Attempt to join group %s failed due to obsolete "
+                     "coordinator information, retrying.", self.group_id)
+            future.failure(error_type())
+        elif error_type in (Errors.InconsistentGroupProtocolError,
+                            Errors.InvalidSessionTimeoutError,
+                            Errors.InvalidGroupIdError):
+            # log the error and re-throw the exception
+            error = error_type(response)
+            log.error("Attempt to join group %s failed due to: %s",
+                      self.group_id, error)
+            future.failure(error)
+        elif error_type is Errors.GroupAuthorizationFailedError:
+            future.failure(error_type(self.group_id))
+        else:
+            # unexpected error, throw the exception
+            error = error_type()
+            log.error("Unexpected error in join group response: %s", error)
+            future.failure(error)
+
+    def _on_join_follower(self):
+        # send follower's sync group with an empty assignment
+        request = SyncGroupRequest(
+            self.group_id,
+            self.generation,
+            self.member_id,
+            {})
+        log.debug("Issuing follower SyncGroup (%s) to coordinator %s",
+                  request, self.coordinator_id)
+        return self._send_sync_group_request(request)
+
+    def _on_join_leader(self, response):
+        """
+        Perform leader synchronization and send back the assignment
+        for the group via SyncGroupRequest
+
+        Arguments:
+            response (JoinResponse): broker response to parse
+
+        Returns:
+            Future: resolves to member assignment encoded-bytes
+        """
+        try:
+            group_assignment = self._perform_assignment(response.leader_id,
+                                                        response.group_protocol,
+                                                        response.members)
+        except Exception as e:
+            return Future().failure(e)
+
+        request = SyncGroupRequest(
+            self.group_id,
+            self.generation,
+            self.member_id,
+            [(member_id,
+              assignment if isinstance(assignment, bytes) else assignment.encode())
+             for member_id, assignment in six.iteritems(group_assignment)])
+
+        log.debug("Issuing leader SyncGroup (%s) to coordinator %s",
+                  request, self.coordinator_id)
+        return self._send_sync_group_request(request)
+
+    def _send_sync_group_request(self, request):
+        if self.coordinator_unknown():
+            return Future().failure(Errors.GroupCoordinatorNotAvailableError())
+        future = Future()
+        _f = self._client.send(self.coordinator_id, request)
+        _f.add_callback(self._handle_sync_group_response, future)
+        _f.add_errback(self._failed_request, self.coordinator_id,
+                       request, future)
+        return future
+
+    def _handle_sync_group_response(self, future, response):
+        error_type = Errors.for_code(response.error_code)
+        if error_type is Errors.NoError:
+            log.debug("Received successful sync group response for group %s: %s",
+                      self.group_id, response)
+            #self.sensors.syncLatency.record(response.requestLatencyMs())
+            future.success(response.member_assignment)
+            return
+
+        # Always rejoin on error
+        self.rejoin_needed = True
+        if error_type is Errors.GroupAuthorizationFailedError:
+            future.failure(error_type(self.group_id))
+        elif error_type is Errors.RebalanceInProgressError:
+            log.info("SyncGroup for group %s failed due to coordinator"
+                     " rebalance, rejoining the group", self.group_id)
+            future.failure(error_type(self.group_id))
+        elif error_type in (Errors.UnknownMemberIdError,
+                            Errors.IllegalGenerationError):
+            error = error_type()
+            log.info("SyncGroup for group %s failed due to %s,"
+                     " rejoining the group", self.group_id, error)
+            self.member_id = JoinGroupRequest.UNKNOWN_MEMBER_ID
+            future.failure(error)
+        elif error_type in (Errors.GroupCoordinatorNotAvailableError,
+                            Errors.NotCoordinatorForGroupError):
+            error = error_type()
+            log.info("SyncGroup for group %s failed due to %s, will find new"
+                     " coordinator and rejoin", self.group_id, error)
+            self.coordinator_dead()
+            future.failure(error)
+        else:
+            error = error_type()
+            log.error("Unexpected error from SyncGroup: %s", error)
+            future.failure(error)
+
+    def _send_group_metadata_request(self):
+        """Discover the current coordinator for the group.
+
+        Returns:
+            Future: resolves to the node id of the coordinator
+        """
+        node_id = self._client.least_loaded_node()
+        if node_id is None or not self._client.ready(node_id):
+            return Future().failure(Errors.NoBrokersAvailable())
+
+        log.debug("Issuing group metadata request to broker %s", node_id)
+        request = GroupCoordinatorRequest(self.group_id)
+        future = Future()
+        _f = self._client.send(node_id, request)
+        _f.add_callback(self._handle_group_coordinator_response, future)
+        _f.add_errback(self._failed_request, node_id, request, future)
+        return future
+
+    def _handle_group_coordinator_response(self, future, response):
+        log.debug("Group metadata response %s", response)
+        if not self.coordinator_unknown():
+            # We already found the coordinator, so ignore the request
+            log.debug("Coordinator already known -- ignoring metadata response")
+            future.success(self.coordinator_id)
+            return
+
+        error_type = Errors.for_code(response.error_code)
+        if error_type is Errors.NoError:
+            ok = self._client.cluster.add_group_coordinator(self.group_id, response)
+            if not ok:
+                # This could happen if coordinator metadata is different
+                # than broker metadata
+                future.failure(Errors.IllegalStateError())
+                return
+
+            self.coordinator_id = response.coordinator_id
+            self._client.ready(self.coordinator_id)
+
+            # start sending heartbeats only if we have a valid generation
+            if self.generation > 0:
+                self.heartbeat_task.reset()
+            future.success(self.coordinator_id)
+        elif error_type is Errors.GroupCoordinatorNotAvailableError:
+            log.debug("Group Coordinator Not Available; retry")
+            future.failure(error_type())
+        elif error_type is Errors.GroupAuthorizationFailedError:
+            error = error_type(self.group_id)
+            log.error("Group Coordinator Request failed: %s", error)
+            future.failure(error)
+        else:
+            error = error_type()
+            log.error("Unrecognized failure in Group Coordinator Request: %s",
+                      error)
+            future.failure(error)
+
+    def coordinator_dead(self, error=None):
+        """Mark the current coordinator as dead."""
+        if self.coordinator_id is not None:
+            log.info("Marking the coordinator dead (node %s): %s.",
+                     self.coordinator_id, error)
+            self.coordinator_id = None
+
+    def close(self):
+        """Close the coordinator, leave the current group
+        and reset local generation/memberId."""
+        try:
+            self._client.unschedule(self.heartbeat_task)
+        except KeyError:
+            pass
+        if not self.coordinator_unknown() and self.generation > 0:
+            # this is a minimal effort attempt to leave the group. we do not
+            # attempt any resending if the request fails or times out.
+            request = LeaveGroupRequest(self.group_id, self.member_id)
+            future = self._client.send(self.coordinator_id, request)
+            future.add_callback(self._handle_leave_group_response)
+            future.add_errback(log.error, "LeaveGroup request failed: %s")
+            self._client.poll(future=future)
+
+        self.generation = OffsetCommitRequest.DEFAULT_GENERATION_ID
+        self.member_id = JoinGroupRequest.UNKNOWN_MEMBER_ID
+        self.rejoin_needed = True
+
+    def _handle_leave_group_response(self, response):
+        error_type = Errors.for_code(response.error_code)
+        if error_type is Errors.NoError:
+            log.info("LeaveGroup request succeeded")
+        else:
+            log.error("LeaveGroup request failed: %s", error_type())
+
+    def _send_heartbeat_request(self):
+        """Send a heartbeat request"""
+        request = HeartbeatRequest(self.group_id, self.generation, self.member_id)
+        log.debug("Heartbeat: %s[%s] %s", request.group, request.generation_id, request.member_id) #pylint: disable-msg=no-member
+        future = Future()
+        _f = self._client.send(self.coordinator_id, request)
+        _f.add_callback(self._handle_heartbeat_response, future)
+        _f.add_errback(self._failed_request, self.coordinator_id,
+                       request, future)
+        return future
+
+    def _handle_heartbeat_response(self, future, response):
+        #self.sensors.heartbeat_latency.record(response.requestLatencyMs())
+        error_type = Errors.for_code(response.error_code)
+        if error_type is Errors.NoError:
+            log.debug("Received successful heartbeat response.")
+            future.success(None)
+        elif error_type in (Errors.GroupCoordinatorNotAvailableError,
+                            Errors.NotCoordinatorForGroupError):
+            log.info("Heartbeat failed: coordinator is either not started or"
+                     " not valid; will refresh metadata and retry")
+            self.coordinator_dead()
+            future.failure(error_type())
+        elif error_type is Errors.RebalanceInProgressError:
+            log.info("Heartbeat failed: group is rebalancing; re-joining group")
+            self.rejoin_needed = True
+            future.failure(error_type())
+        elif error_type is Errors.IllegalGenerationError:
+            log.info("Heartbeat failed: local generation id is not current;"
+                     " re-joining group")
+            self.rejoin_needed = True
+            future.failure(error_type())
+        elif error_type is Errors.UnknownMemberIdError:
+            log.info("Heartbeat failed: local member_id was not recognized;"
+                     " resetting and re-joining group")
+            self.member_id = JoinGroupRequest.UNKNOWN_MEMBER_ID
+            self.rejoin_needed = True
+            future.failure(error_type)
+        elif error_type is Errors.GroupAuthorizationFailedError:
+            error = error_type(self.group_id)
+            log.error("Heartbeat failed: authorization error: %s", error)
+            future.failure(error)
+        else:
+            error = error_type()
+            log.error("Heartbeat failed: Unhandled error: %s", error)
+            future.failure(error)
+
+
+class HeartbeatTask(object):
+    def __init__(self, coordinator):
+        self._coordinator = coordinator
+        self._heartbeat = coordinator.heartbeat
+        self._client = coordinator._client
+        self._request_in_flight = False
+
+    def reset(self):
+        # start or restart the heartbeat task to be executed at the next chance
+        self._heartbeat.reset_session_timeout()
+        try:
+            self._client.unschedule(self)
+        except KeyError:
+            pass
+        if not self._request_in_flight:
+            self._client.schedule(self, time.time())
+
+    def __call__(self):
+        if (self._coordinator.generation < 0 or
+            self._coordinator.need_rejoin() or
+            self._coordinator.coordinator_unknown()):
+            # no need to send the heartbeat we're not using auto-assignment
+            # or if we are awaiting a rebalance
+            log.debug("Skipping heartbeat: no auto-assignment"
+                      " or waiting on rebalance")
+            return
+
+        if self._heartbeat.session_expired():
+            # we haven't received a successful heartbeat in one session interval
+            # so mark the coordinator dead
+            log.error("Heartbeat session expired - marking coordinator dead")
+            self._coordinator.coordinator_dead()
+            return
+
+        if not self._heartbeat.should_heartbeat():
+            # we don't need to heartbeat now, so reschedule for when we do
+            ttl = self._heartbeat.ttl()
+            log.debug("Heartbeat task unneeded now, retrying in %s", ttl)
+            self._client.schedule(self, time.time() + ttl)
+        else:
+            self._heartbeat.sent_heartbeat()
+            self._request_in_flight = True
+            future = self._coordinator._send_heartbeat_request()
+            future.add_callback(self._handle_heartbeat_success)
+            future.add_errback(self._handle_heartbeat_failure)
+
+    def _handle_heartbeat_success(self, v):
+        log.debug("Received successful heartbeat")
+        self._request_in_flight = False
+        self._heartbeat.received_heartbeat()
+        ttl = self._heartbeat.ttl()
+        self._client.schedule(self, time.time() + ttl)
+
+    def _handle_heartbeat_failure(self, e):
+        log.debug("Heartbeat failed; retrying")
+        self._request_in_flight = False
+        etd = time.time() + self._coordinator.config['retry_backoff_ms'] / 1000.0
+        self._client.schedule(self, etd)
+
+
+class GroupCoordinatorMetrics(object):
+    def __init__(self, metrics, prefix, tags=None):
+        self.metrics = metrics
+        self.group_name = prefix + "-coordinator-metrics"
+
+        self.heartbeat_latency = metrics.sensor("heartbeat-latency")
+        self.heartbeat_latency.add(metrics.metricName(
+            "heartbeat-response-time-max", self.group_name,
+            "The max time taken to receive a response to a heartbeat request",
+            tags), metrics.Max())
+        self.heartbeat_latency.add(metrics.metricName(
+            "heartbeat-rate", self.group_name,
+            "The average number of heartbeats per second",
+            tags), metrics.Rate(metrics.Count()))
+
+        self.join_latency = metrics.sensor("join-latency")
+        self.join_latency.add(metrics.metricName(
+            "join-time-avg", self.group_name,
+            "The average time taken for a group rejoin",
+            tags), metrics.Avg())
+        self.join_latency.add(metrics.metricName(
+            "join-time-max", self.group_name,
+            "The max time taken for a group rejoin",
+            tags), metrics.Avg())
+        self.join_latency.add(metrics.metricName(
+            "join-rate", self.group_name,
+            "The number of group joins per second",
+            tags), metrics.Rate(metrics.Count()))
+
+        self.sync_latency = metrics.sensor("sync-latency")
+        self.sync_latency.add(metrics.metricName(
+            "sync-time-avg", self.group_name,
+            "The average time taken for a group sync",
+            tags), metrics.Avg())
+        self.sync_latency.add(metrics.MetricName(
+            "sync-time-max", self.group_name,
+            "The max time taken for a group sync",
+            tags), metrics.Avg())
+        self.sync_latency.add(metrics.metricName(
+            "sync-rate", self.group_name,
+            "The number of group syncs per second",
+            tags), metrics.Rate(metrics.Count()))
+
+        """
+        lastHeartbeat = Measurable(
+            measure=lambda _, value: value - heartbeat.last_heartbeat_send()
+        )
+        metrics.addMetric(metrics.metricName(
+            "last-heartbeat-seconds-ago", self.group_name,
+            "The number of seconds since the last controller heartbeat",
+            tags), lastHeartbeat)
+        """
+
+