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# 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.

"""
Simple Scheduler
"""

import datetime

from nova import db
from nova import flags
from nova.scheduler import driver
from nova.scheduler import chance

FLAGS = flags.FLAGS
flags.DEFINE_integer("max_cores", 16,
                     "maximum number of instance cores to allow per host")
flags.DEFINE_integer("max_gigabytes", 10000,
                     "maximum number of volume gigabytes to allow per host")
flags.DEFINE_integer("max_networks", 1000,
                     "maximum number of networks to allow per host")


class SimpleScheduler(chance.ChanceScheduler):
    """Implements Naive Scheduler that tries to find least loaded host."""

    def schedule_run_instance(self, context, instance_id, *_args, **_kwargs):
        """Picks a host that is up and has the fewest running instances."""
        instance_ref = db.instance_get(context, instance_id)
        results = db.service_get_all_compute_sorted(context)
        for result in results:
            (service, instance_cores) = result
            if instance_cores + instance_ref['vcpus'] > FLAGS.max_cores:
                raise driver.NoValidHost("All hosts have too many cores")
            if self.service_is_up(service):
                # NOTE(vish): this probably belongs in the manager, if we
                #             can generalize this somehow
                now = datetime.datetime.utcnow()
                db.instance_update(context,
                                   instance_id,
                                   {'host': service['host'],
                                    'scheduled_at': now})
                return service['host']
        raise driver.NoValidHost("No hosts found")

    def schedule_create_volume(self, context, volume_id, *_args, **_kwargs):
        """Picks a host that is up and has the fewest volumes."""
        volume_ref = db.volume_get(context, volume_id)
        results = db.service_get_all_volume_sorted(context)
        for result in results:
            (service, volume_gigabytes) = result
            if volume_gigabytes + volume_ref['size'] > FLAGS.max_gigabytes:
                raise driver.NoValidHost("All hosts have too many gigabytes")
            if self.service_is_up(service):
                # NOTE(vish): this probably belongs in the manager, if we
                #             can generalize this somehow
                now = datetime.datetime.utcnow()
                db.volume_update(context,
                                 volume_id,
                                 {'host': service['host'],
                                  'scheduled_at': now})
                return service['host']
        raise driver.NoValidHost("No hosts found")

    def schedule_set_network_host(self, context, *_args, **_kwargs):
        """Picks a host that is up and has the fewest networks."""

        results = db.service_get_all_network_sorted(context)
        for result in results:
            (service, instance_count) = result
            if instance_count >= FLAGS.max_networks:
                raise driver.NoValidHost("All hosts have too many networks")
            if self.service_is_up(service):
                return service['host']
        raise driver.NoValidHost("No hosts found")