from __future__ import absolute_import, division
import abc
import copy
import logging
import time
import weakref
from kafka.vendor import six
from .heartbeat import Heartbeat
from .. import errors as Errors
from ..future import Future
from ..metrics import AnonMeasurable
from ..metrics.stats import Avg, Count, Max, Rate
from ..protocol.commit import GroupCoordinatorRequest, OffsetCommitRequest
from ..protocol.group import (HeartbeatRequest, JoinGroupRequest,
LeaveGroupRequest, SyncGroupRequest)
log = logging.getLogger('kafka.coordinator')
[docs]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,
'api_version': (0, 9),
'metric_group_prefix': '',
}
def __init__(self, client, metrics, **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[2].DEFAULT_GENERATION_ID
self.member_id = JoinGroupRequest[0].UNKNOWN_MEMBER_ID
self.group_id = self.config['group_id']
self.coordinator_id = None
self.rejoin_needed = True
self.rejoining = False
self.heartbeat = Heartbeat(**self.config)
self.heartbeat_task = HeartbeatTask(weakref.proxy(self))
self.sensors = GroupCoordinatorMetrics(self.heartbeat, metrics,
self.config['metric_group_prefix'])
def __del__(self):
if hasattr(self, 'heartbeat_task') and self.heartbeat_task:
self.heartbeat_task.disable()
@abc.abstractmethod
[docs] 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
[docs] 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
[docs] 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 False
[docs] 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():
# Prior to 0.8.2 there was no group coordinator
# so we will just pick a node at random and treat
# it as the "coordinator"
if self.config['api_version'] < (0, 8, 2):
self.coordinator_id = self._client.least_loaded_node()
self._client.ready(self.coordinator_id)
continue
future = self._send_group_coordinator_request()
self._client.poll(future=future)
if future.failed():
if isinstance(future.exception,
Errors.GroupCoordinatorNotAvailableError):
continue
elif 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
[docs] 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
[docs] def ensure_active_group(self):
"""Ensure that the group is active (i.e. joined and synced)"""
if not self.need_rejoin():
return
if not self.rejoining:
self._on_join_prepare(self.generation, self.member_id)
self.rejoining = True
while self.need_rejoin():
self.ensure_coordinator_known()
# ensure that there are no pending requests to the coordinator.
# This is important in particular to avoid resending a pending
# JoinGroup request.
if self._client.in_flight_request_count(self.coordinator_id):
while self._client.in_flight_request_count(self.coordinator_id):
self._client.poll()
continue
future = self._send_join_group_request()
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.rejoining = False
self.heartbeat_task.reset()
else:
assert future.failed()
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)
def _send_join_group_request(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.info("(Re-)joining group %s", self.group_id)
request = JoinGroupRequest[0](
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("Sending JoinGroup (%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, time.time())
_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]',
request.__class__.__name__, node_id, error)
# Marking coordinator dead
# unless the error is caused by internal client pipelining
if not isinstance(error, (Errors.NodeNotReadyError,
Errors.TooManyInFlightRequests)):
self.coordinator_dead()
future.failure(error)
def _handle_join_group_response(self, future, send_time, response):
error_type = Errors.for_code(response.error_code)
if error_type is Errors.NoError:
log.debug("Received successful JoinGroup response for group %s: %s",
self.group_id, response)
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((time.time() - send_time) * 1000)
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 %s"
" is loading the group.", self.group_id, self.coordinator_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[0].UNKNOWN_MEMBER_ID
log.debug("Attempt to join group %s failed due to unknown member id",
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.debug("Attempt to join group %s failed due to obsolete "
"coordinator information: %s", self.group_id,
error_type.__name__)
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 fatal error: %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[0](
self.group_id,
self.generation,
self.member_id,
{})
log.debug("Sending follower SyncGroup for group %s to coordinator %s: %s",
self.group_id, self.coordinator_id, request)
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[0](
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("Sending leader SyncGroup for group %s to coordinator %s: %s",
self.group_id, self.coordinator_id, request)
return self._send_sync_group_request(request)
def _send_sync_group_request(self, request):
if self.coordinator_unknown():
e = Errors.GroupCoordinatorNotAvailableError(self.coordinator_id)
return Future().failure(e)
future = Future()
_f = self._client.send(self.coordinator_id, request)
_f.add_callback(self._handle_sync_group_response, future, time.time())
_f.add_errback(self._failed_request, self.coordinator_id,
request, future)
return future
def _handle_sync_group_response(self, future, send_time, response):
error_type = Errors.for_code(response.error_code)
if error_type is Errors.NoError:
log.info("Successfully joined group %s with generation %s",
self.group_id, self.generation)
self.sensors.sync_latency.record((time.time() - send_time) * 1000)
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.debug("SyncGroup for group %s failed due to coordinator"
" rebalance", self.group_id)
future.failure(error_type(self.group_id))
elif error_type in (Errors.UnknownMemberIdError,
Errors.IllegalGenerationError):
error = error_type()
log.debug("SyncGroup for group %s failed due to %s", self.group_id, error)
self.member_id = JoinGroupRequest[0].UNKNOWN_MEMBER_ID
future.failure(error)
elif error_type in (Errors.GroupCoordinatorNotAvailableError,
Errors.NotCoordinatorForGroupError):
error = error_type()
log.debug("SyncGroup for group %s failed due to %s", 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_coordinator_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:
return Future().failure(Errors.NoBrokersAvailable())
log.debug("Sending group coordinator request for group %s to broker %s",
self.group_id, node_id)
request = GroupCoordinatorRequest[0](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("Received group coordinator 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
log.info("Discovered coordinator %s for group %s",
self.coordinator_id, self.group_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)
[docs] def coordinator_dead(self, error=None):
"""Mark the current coordinator as dead."""
if self.coordinator_id is not None:
log.warning("Marking the coordinator dead (node %s) for group %s: %s.",
self.coordinator_id, self.group_id, error)
self.coordinator_id = None
[docs] 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[0](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[2].DEFAULT_GENERATION_ID
self.member_id = JoinGroupRequest[0].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[0](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, time.time())
_f.add_errback(self._failed_request, self.coordinator_id,
request, future)
return future
def _handle_heartbeat_response(self, future, send_time, response):
self.sensors.heartbeat_latency.record((time.time() - send_time) * 1000)
error_type = Errors.for_code(response.error_code)
if error_type is Errors.NoError:
log.debug("Received successful heartbeat response for group %s",
self.group_id)
future.success(None)
elif error_type in (Errors.GroupCoordinatorNotAvailableError,
Errors.NotCoordinatorForGroupError):
log.warning("Heartbeat failed for group %s: coordinator (node %s)"
" is either not started or not valid", self.group_id,
self.coordinator_id)
self.coordinator_dead()
future.failure(error_type())
elif error_type is Errors.RebalanceInProgressError:
log.warning("Heartbeat failed for group %s because it is"
" rebalancing", self.group_id)
self.rejoin_needed = True
future.failure(error_type())
elif error_type is Errors.IllegalGenerationError:
log.warning("Heartbeat failed for group %s: generation id is not "
" current.", self.group_id)
self.rejoin_needed = True
future.failure(error_type())
elif error_type is Errors.UnknownMemberIdError:
log.warning("Heartbeat: local member_id was not recognized;"
" this consumer needs to re-join")
self.member_id = JoinGroupRequest[0].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)
[docs]class HeartbeatTask(object):
def __init__(self, coordinator):
self._coordinator = coordinator
self._heartbeat = coordinator.heartbeat
self._client = coordinator._client
self._request_in_flight = False
[docs] def disable(self):
try:
self._client.unschedule(self)
except KeyError:
pass
[docs] 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()):
# no need to send the heartbeat we're not using auto-assignment
# or if we are awaiting a rebalance
log.info("Skipping heartbeat: no auto-assignment"
" or waiting on rebalance")
return
if self._coordinator.coordinator_unknown():
log.warning("Coordinator unknown during heartbeat -- will retry")
self._handle_heartbeat_failure(Errors.GroupCoordinatorNotAvailableError())
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.warning("Heartbeat failed (%s); retrying", e)
self._request_in_flight = False
etd = time.time() + self._coordinator.config['retry_backoff_ms'] / 1000
self._client.schedule(self, etd)
[docs]class GroupCoordinatorMetrics(object):
def __init__(self, heartbeat, metrics, prefix, tags=None):
self.heartbeat = heartbeat
self.metrics = metrics
self.metric_group_name = prefix + "-coordinator-metrics"
self.heartbeat_latency = metrics.sensor('heartbeat-latency')
self.heartbeat_latency.add(metrics.metric_name(
'heartbeat-response-time-max', self.metric_group_name,
'The max time taken to receive a response to a heartbeat request',
tags), Max())
self.heartbeat_latency.add(metrics.metric_name(
'heartbeat-rate', self.metric_group_name,
'The average number of heartbeats per second',
tags), Rate(sampled_stat=Count()))
self.join_latency = metrics.sensor('join-latency')
self.join_latency.add(metrics.metric_name(
'join-time-avg', self.metric_group_name,
'The average time taken for a group rejoin',
tags), Avg())
self.join_latency.add(metrics.metric_name(
'join-time-max', self.metric_group_name,
'The max time taken for a group rejoin',
tags), Avg())
self.join_latency.add(metrics.metric_name(
'join-rate', self.metric_group_name,
'The number of group joins per second',
tags), Rate(sampled_stat=Count()))
self.sync_latency = metrics.sensor('sync-latency')
self.sync_latency.add(metrics.metric_name(
'sync-time-avg', self.metric_group_name,
'The average time taken for a group sync',
tags), Avg())
self.sync_latency.add(metrics.metric_name(
'sync-time-max', self.metric_group_name,
'The max time taken for a group sync',
tags), Avg())
self.sync_latency.add(metrics.metric_name(
'sync-rate', self.metric_group_name,
'The number of group syncs per second',
tags), Rate(sampled_stat=Count()))
metrics.add_metric(metrics.metric_name(
'last-heartbeat-seconds-ago', self.metric_group_name,
'The number of seconds since the last controller heartbeat',
tags), AnonMeasurable(
lambda _, now: (now / 1000) - self.heartbeat.last_send))