/usr/lib/python2.7/dist-packages/aodh/coordination.py is in python-aodh 2.0.0-0ubuntu1.
This file is owned by root:root, with mode 0o644.
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# Copyright 2014 Red Hat, 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 bisect
import hashlib
import struct
import uuid
from oslo_config import cfg
from oslo_log import log
import six
import tooz.coordination
from aodh.i18n import _LE, _LI
LOG = log.getLogger(__name__)
OPTS = [
cfg.StrOpt('backend_url',
help='The backend URL to use for distributed coordination. If '
'left empty, per-deployment central agent and per-host '
'compute agent won\'t do workload '
'partitioning and will only function correctly if a '
'single instance of that service is running.'),
cfg.FloatOpt('heartbeat',
default=1.0,
help='Number of seconds between heartbeats for distributed '
'coordination.'),
cfg.FloatOpt('check_watchers',
default=10.0,
help='Number of seconds between checks to see if group '
'membership has changed')
]
class HashRing(object):
def __init__(self, nodes, replicas=100):
self._ring = dict()
self._sorted_keys = []
for node in nodes:
for r in six.moves.range(replicas):
hashed_key = self._hash('%s-%s' % (node, r))
self._ring[hashed_key] = node
self._sorted_keys.append(hashed_key)
self._sorted_keys.sort()
@staticmethod
def _hash(key):
return struct.unpack_from('>I',
hashlib.md5(str(key).encode()).digest())[0]
def _get_position_on_ring(self, key):
hashed_key = self._hash(key)
position = bisect.bisect(self._sorted_keys, hashed_key)
return position if position < len(self._sorted_keys) else 0
def get_node(self, key):
if not self._ring:
return None
pos = self._get_position_on_ring(key)
return self._ring[self._sorted_keys[pos]]
class PartitionCoordinator(object):
"""Workload partitioning coordinator.
This class uses the `tooz` library to manage group membership.
To ensure that the other agents know this agent is still alive,
the `heartbeat` method should be called periodically.
Coordination errors and reconnects are handled under the hood, so the
service using the partition coordinator need not care whether the
coordination backend is down. The `extract_my_subset` will simply return an
empty iterable in this case.
"""
def __init__(self, backend_url, my_id=None):
self.backend_url = backend_url
self._coordinator = None
self._groups = set()
self._my_id = my_id or str(uuid.uuid4())
self._started = False
def start(self):
if self.backend_url:
try:
self._coordinator = tooz.coordination.get_coordinator(
self.backend_url, self._my_id)
self._coordinator.start()
self._started = True
LOG.info(_LI('Coordination backend started successfully.'))
except tooz.coordination.ToozError:
self._started = False
LOG.exception(_LE('Error connecting to coordination backend.'))
def stop(self):
if not self._coordinator:
return
for group in list(self._groups):
self.leave_group(group)
try:
self._coordinator.stop()
except tooz.coordination.ToozError:
LOG.exception(_LE('Error connecting to coordination backend.'))
finally:
self._coordinator = None
self._started = False
def is_active(self):
return self._coordinator is not None
def heartbeat(self):
if self._coordinator:
if not self._started:
# re-connect
self.start()
try:
self._coordinator.heartbeat()
except tooz.coordination.ToozError:
LOG.exception(_LE('Error sending a heartbeat to coordination '
'backend.'))
def watch_group(self, namespace, callback):
if self._coordinator:
self._coordinator.watch_join_group(namespace, callback)
self._coordinator.watch_leave_group(namespace, callback)
def run_watchers(self):
if self._coordinator:
self._coordinator.run_watchers()
def join_group(self, group_id):
if not self._coordinator or not self._started or not group_id:
return
while True:
try:
join_req = self._coordinator.join_group(group_id)
join_req.get()
LOG.info(_LI('Joined partitioning group %s'), group_id)
break
except tooz.coordination.MemberAlreadyExist:
return
except tooz.coordination.GroupNotCreated:
create_grp_req = self._coordinator.create_group(group_id)
try:
create_grp_req.get()
except tooz.coordination.GroupAlreadyExist:
pass
self._groups.add(group_id)
def leave_group(self, group_id):
if group_id not in self._groups:
return
if self._coordinator:
self._coordinator.leave_group(group_id)
self._groups.remove(group_id)
LOG.info(_LI('Left partitioning group %s'), group_id)
def _get_members(self, group_id):
if not self._coordinator:
return [self._my_id]
while True:
get_members_req = self._coordinator.get_members(group_id)
try:
return get_members_req.get()
except tooz.coordination.GroupNotCreated:
self.join_group(group_id)
def extract_my_subset(self, group_id, iterable):
"""Filters an iterable, returning only objects assigned to this agent.
We have a list of objects and get a list of active group members from
`tooz`. We then hash all the objects into buckets and return only
the ones that hashed into *our* bucket.
"""
if not group_id:
return iterable
if group_id not in self._groups:
self.join_group(group_id)
try:
members = self._get_members(group_id)
LOG.debug('Members of group: %s', members)
hr = HashRing(members)
filtered = [v for v in iterable
if hr.get_node(str(v)) == self._my_id]
LOG.debug('My subset: %s', filtered)
return filtered
except tooz.coordination.ToozError:
LOG.exception(_LE('Error getting group membership info from '
'coordination backend.'))
return []
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