deb-mistral/mistral/coordination.py
LingxianKong c780938453 Raise user-friendly exception in case of connection failed
In the scenario of network interruption or connection manually shutdown,
the service api can't be used any more, we should catch the exception.

Change-Id: I276cdb70e35b14504c7139604066098703d9edec
Closes-Bug: #1484804
2015-08-19 10:40:43 +08:00

210 lines
5.9 KiB
Python

# Copyright 2015 Huawei Technologies Co., Ltd.
#
# 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 six
from oslo_concurrency import lockutils
from oslo_config import cfg
from oslo_log import log
from oslo_service import threadgroup
from retrying import retry
import tooz.coordination
from mistral import utils
LOG = log.getLogger(__name__)
_SERVICE_COORDINATOR = None
class ServiceCoordinator(object):
"""Service 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.
"""
def __init__(self, my_id=None):
self._coordinator = None
self._my_id = my_id or utils.get_process_identifier()
self._started = False
def start(self):
backend_url = cfg.CONF.coordination.backend_url
if backend_url:
try:
self._coordinator = tooz.coordination.get_coordinator(
backend_url,
self._my_id
)
self._coordinator.start()
self._started = True
LOG.info('Coordination backend started successfully.')
except tooz.coordination.ToozError as e:
self._started = False
LOG.exception('Error connecting to coordination backend. '
'%s', six.text_type(e))
def stop(self):
if not self.is_active():
return
try:
self._coordinator.stop()
except tooz.coordination.ToozError:
LOG.warning('Error connecting to coordination backend.')
finally:
self._coordinator = None
self._started = False
def is_active(self):
return self._coordinator and self._started
def heartbeat(self):
if not self.is_active():
# Re-connect.
self.start()
if not self.is_active():
LOG.debug("Coordination backend didn't start.")
return
try:
self._coordinator.heartbeat()
except tooz.coordination.ToozError as e:
LOG.exception('Error sending a heartbeat to coordination '
'backend. %s', six.text_type(e))
self._started = False
@retry(stop_max_attempt_number=5)
def join_group(self, group_id):
if not self.is_active() or not group_id:
return
try:
join_req = self._coordinator.join_group(group_id)
join_req.get()
LOG.info(
'Joined service group:%s, member:%s',
group_id,
self._my_id
)
return
except tooz.coordination.MemberAlreadyExist:
return
except tooz.coordination.GroupNotCreated as e:
create_grp_req = self._coordinator.create_group(group_id)
try:
create_grp_req.get()
except tooz.coordination.GroupAlreadyExist:
pass
# Re-raise exception to join group again.
raise e
def leave_group(self, group_id):
if self.is_active():
self._coordinator.leave_group(group_id)
LOG.info(
'Left service group:%s, member:%s',
group_id,
self._my_id
)
def get_members(self, group_id):
"""Gets members of coordination group.
ToozError exception must be handled when this function is invoded, we
leave it to the invoker for the handling decision.
"""
if not self.is_active():
return []
get_members_req = self._coordinator.get_members(group_id)
try:
members = get_members_req.get()
LOG.debug('Members of group %s: %s', group_id, members)
return members
except tooz.coordination.GroupNotCreated:
LOG.warning('Group %s does not exist.', group_id)
return []
def cleanup_service_coordinator():
"""Intends to be used by tests to recreate service coordinator."""
global _SERVICE_COORDINATOR
_SERVICE_COORDINATOR = None
def get_service_coordinator(my_id=None):
global _SERVICE_COORDINATOR
if not _SERVICE_COORDINATOR:
_SERVICE_COORDINATOR = ServiceCoordinator(my_id=my_id)
_SERVICE_COORDINATOR.start()
return _SERVICE_COORDINATOR
class Service(object):
def __init__(self, group_type):
self.group_type = group_type
self._tg = None
@lockutils.synchronized('service_coordinator')
def register_membership(self):
"""Registers group membership.
Because this method will be invoked on each service startup almost at
the same time, so it must be synchronized, in case all the services
are started within same process.
"""
service_coordinator = get_service_coordinator()
if service_coordinator.is_active():
service_coordinator.join_group(self.group_type)
self._tg = threadgroup.ThreadGroup()
self._tg.add_timer(
cfg.CONF.coordination.heartbeat_interval,
service_coordinator.heartbeat
)
def stop(self):
service_coordinator = get_service_coordinator()
if service_coordinator.is_active():
self._tg.stop()
service_coordinator.stop()