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# vim: tabstop=4 shiftwidth=4 softtabstop=4
# Copyright (c) 2010 Openstack, LLC.
# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# All Rights Reserved.
#
# 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.
"""
Scheduler base class that all Schedulers should inherit from
"""
import datetime
from nova import db
from nova import exception
from nova import flags
FLAGS = flags.FLAGS
flags.DEFINE_integer('service_down_time', 60,
'maximum time since last checkin for up service')
class NoValidHost(exception.Error):
"""There is no valid host for the command."""
pass
class WillNotSchedule(exception.Error):
"""The specified host is not up or doesn't exist."""
pass
class Scheduler(object):
"""The base class that all Scheduler clases should inherit from."""
@staticmethod
def service_is_up(service):
"""Check whether a service is up based on last heartbeat."""
last_heartbeat = service['updated_at'] or service['created_at']
# Timestamps in DB are UTC.
elapsed = datetime.datetime.utcnow() - last_heartbeat
return elapsed < datetime.timedelta(seconds=FLAGS.service_down_time)
def hosts_up(self, context, topic):
"""Return the list of hosts that have a running service for topic."""
services = db.service_get_all_by_topic(context, topic)
return [service.host
for service in services
if self.service_is_up(service)]
def schedule(self, context, topic, *_args, **_kwargs):
"""Must override at least this method for scheduler to work."""
raise NotImplementedError(_("Must implement a fallback schedule"))
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