path: root/nova/conductor/manager.py

#    Copyright 2013 IBM Corp.
#
#    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.

"""Handles database requests from other nova services."""

import copy

from oslo_config import cfg
from oslo_log import log as logging
import oslo_messaging as messaging
from oslo_utils import excutils
from oslo_utils import versionutils
import six

from nova.compute import rpcapi as compute_rpcapi
from nova.compute import task_states
from nova.compute import utils as compute_utils
from nova.compute.utils import wrap_instance_event
from nova.compute import vm_states
from nova.conductor.tasks import live_migrate
from nova.conductor.tasks import migrate
from nova.db import base
from nova import exception
from nova.i18n import _, _LE, _LI, _LW
from nova import image
from nova import manager
from nova import network
from nova import objects
from nova.objects import base as nova_object
from nova import rpc
from nova.scheduler import client as scheduler_client
from nova.scheduler import utils as scheduler_utils
from nova import servicegroup
from nova import utils

LOG = logging.getLogger(__name__)
CONF = cfg.CONF


class ConductorManager(manager.Manager):
    """Mission: Conduct things.

    The methods in the base API for nova-conductor are various proxy operations
    performed on behalf of the nova-compute service running on compute nodes.
    Compute nodes are not allowed to directly access the database, so this set
    of methods allows them to get specific work done without locally accessing
    the database.

    The nova-conductor service also exposes an API in the 'compute_task'
    namespace.  See the ComputeTaskManager class for details.
    """

    target = messaging.Target(version='3.0')

    def __init__(self, *args, **kwargs):
        super(ConductorManager, self).__init__(service_name='conductor',
                                               *args, **kwargs)
        self.compute_task_mgr = ComputeTaskManager()
        self.additional_endpoints.append(self.compute_task_mgr)

    # NOTE(hanlind): This can be removed in version 4.0 of the RPC API
    def provider_fw_rule_get_all(self, context):
        # NOTE(hanlind): Simulate an empty db result for compat reasons.
        return []

    def _object_dispatch(self, target, method, args, kwargs):
        """Dispatch a call to an object method.

        This ensures that object methods get called and any exception
        that is raised gets wrapped in an ExpectedException for forwarding
        back to the caller (without spamming the conductor logs).
        """
        try:
            # NOTE(danms): Keep the getattr inside the try block since
            # a missing method is really a client problem
            return getattr(target, method)(*args, **kwargs)
        except Exception:
            raise messaging.ExpectedException()

    def object_class_action_versions(self, context, objname, objmethod,
                                     object_versions, args, kwargs):
        objclass = nova_object.NovaObject.obj_class_from_name(
            objname, object_versions[objname])
        args = tuple([context] + list(args))
        result = self._object_dispatch(objclass, objmethod, args, kwargs)
        # NOTE(danms): The RPC layer will convert to primitives for us,
        # but in this case, we need to honor the version the client is
        # asking for, so we do it before returning here.
        # NOTE(hanlind): Do not convert older than requested objects,
        # see bug #1596119.
        if isinstance(result, nova_object.NovaObject):
            target_version = object_versions[objname]
            requested_version = versionutils.convert_version_to_tuple(
                target_version)
            actual_version = versionutils.convert_version_to_tuple(
                result.VERSION)
            do_backport = requested_version < actual_version
            other_major_version = requested_version[0] != actual_version[0]
            if do_backport or other_major_version:
                result = result.obj_to_primitive(
                    target_version=target_version,
                    version_manifest=object_versions)
        return result

    def object_action(self, context, objinst, objmethod, args, kwargs):
        """Perform an action on an object."""
        oldobj = objinst.obj_clone()
        result = self._object_dispatch(objinst, objmethod, args, kwargs)
        updates = dict()
        # NOTE(danms): Diff the object with the one passed to us and
        # generate a list of changes to forward back
        for name, field in objinst.fields.items():
            if not objinst.obj_attr_is_set(name):
                # Avoid demand-loading anything
                continue
            if (not oldobj.obj_attr_is_set(name) or
                    getattr(oldobj, name) != getattr(objinst, name)):
                updates[name] = field.to_primitive(objinst, name,
                                                   getattr(objinst, name))
        # This is safe since a field named this would conflict with the
        # method anyway
        updates['obj_what_changed'] = objinst.obj_what_changed()
        return updates, result

    def object_backport_versions(self, context, objinst, object_versions):
        target = object_versions[objinst.obj_name()]
        LOG.debug('Backporting %(obj)s to %(ver)s with versions %(manifest)s',
                  {'obj': objinst.obj_name(),
                   'ver': target,
                   'manifest': ','.join(
                       ['%s=%s' % (name, ver)
                       for name, ver in object_versions.items()])})
        return objinst.obj_to_primitive(target_version=target,
                                        version_manifest=object_versions)

    def reset(self):
        objects.Service.clear_min_version_cache()


class ComputeTaskManager(base.Base):
    """Namespace for compute methods.

    This class presents an rpc API for nova-conductor under the 'compute_task'
    namespace.  The methods here are compute operations that are invoked
    by the API service.  These methods see the operation to completion, which
    may involve coordinating activities on multiple compute nodes.
    """

    target = messaging.Target(namespace='compute_task', version='1.15')

    def __init__(self):
        super(ComputeTaskManager, self).__init__()
        self.compute_rpcapi = compute_rpcapi.ComputeAPI()
        self.image_api = image.API()
        self.network_api = network.API()
        self.servicegroup_api = servicegroup.API()
        self.scheduler_client = scheduler_client.SchedulerClient()
        self.notifier = rpc.get_notifier('compute', CONF.host)

    def reset(self):
        LOG.info(_LI('Reloading compute RPC API'))
        compute_rpcapi.LAST_VERSION = None
        self.compute_rpcapi = compute_rpcapi.ComputeAPI()

    # TODO(tdurakov): remove `live` parameter here on compute task api RPC
    # version bump to 2.x
    @messaging.expected_exceptions(
        exception.NoValidHost,
        exception.ComputeServiceUnavailable,
        exception.ComputeHostNotFound,
        exception.InvalidHypervisorType,
        exception.InvalidCPUInfo,
        exception.UnableToMigrateToSelf,
        exception.DestinationHypervisorTooOld,
        exception.InvalidLocalStorage,
        exception.InvalidSharedStorage,
        exception.HypervisorUnavailable,
        exception.InstanceInvalidState,
        exception.MigrationPreCheckError,
        exception.MigrationPreCheckClientException,
        exception.LiveMigrationWithOldNovaNotSupported,
        exception.UnsupportedPolicyException)
    @wrap_instance_event(prefix='conductor')
    def migrate_server(self, context, instance, scheduler_hint, live, rebuild,
            flavor, block_migration, disk_over_commit, reservations=None,
            clean_shutdown=True, request_spec=None):
        if instance and not isinstance(instance, nova_object.NovaObject):
            # NOTE(danms): Until v2 of the RPC API, we need to tolerate
            # old-world instance objects here
            attrs = ['metadata', 'system_metadata', 'info_cache',
                     'security_groups']
            instance = objects.Instance._from_db_object(
                context, objects.Instance(), instance,
                expected_attrs=attrs)
        # NOTE: Remove this when we drop support for v1 of the RPC API
        if flavor and not isinstance(flavor, objects.Flavor):
            # Code downstream may expect extra_specs to be populated since it
            # is receiving an object, so lookup the flavor to ensure this.
            flavor = objects.Flavor.get_by_id(context, flavor['id'])
        if live and not rebuild and not flavor:
            self._live_migrate(context, instance, scheduler_hint,
                               block_migration, disk_over_commit, request_spec)
        elif not live and not rebuild and flavor:
            instance_uuid = instance.uuid
            with compute_utils.EventReporter(context, 'cold_migrate',
                                             instance_uuid):
                self._cold_migrate(context, instance, flavor,
                                   scheduler_hint['filter_properties'],
                                   reservations, clean_shutdown, request_spec)
        else:
            raise NotImplementedError()

    def _cold_migrate(self, context, instance, flavor, filter_properties,
                      reservations, clean_shutdown, request_spec):
        image = utils.get_image_from_system_metadata(
            instance.system_metadata)

        # NOTE(sbauza): If a reschedule occurs when prep_resize(), then
        # it only provides filter_properties legacy dict back to the
        # conductor with no RequestSpec part of the payload.
        if not request_spec:
            # Make sure we hydrate a new RequestSpec object with the new flavor
            # and not the nested one from the instance
            request_spec = objects.RequestSpec.from_components(
                context, instance.uuid, image,
                flavor, instance.numa_topology, instance.pci_requests,
                filter_properties, None, instance.availability_zone)
        else:
            # NOTE(sbauza): Resizes means new flavor, so we need to update the
            # original RequestSpec object for make sure the scheduler verifies
            # the right one and not the original flavor
            request_spec.flavor = flavor

        task = self._build_cold_migrate_task(context, instance, flavor,
                                             request_spec,
                                             reservations, clean_shutdown)
        # TODO(sbauza): Provide directly the RequestSpec object once
        # _set_vm_state_and_notify() accepts it
        legacy_spec = request_spec.to_legacy_request_spec_dict()
        try:
            task.execute()
        except exception.NoValidHost as ex:
            vm_state = instance.vm_state
            if not vm_state:
                vm_state = vm_states.ACTIVE
            updates = {'vm_state': vm_state, 'task_state': None}
            self._set_vm_state_and_notify(context, instance.uuid,
                                          'migrate_server',
                                          updates, ex, legacy_spec)

            # if the flavor IDs match, it's migrate; otherwise resize
            if flavor.id == instance.instance_type_id:
                msg = _("No valid host found for cold migrate")
            else:
                msg = _("No valid host found for resize")
            raise exception.NoValidHost(reason=msg)
        except exception.UnsupportedPolicyException as ex:
            with excutils.save_and_reraise_exception():
                vm_state = instance.vm_state
                if not vm_state:
                    vm_state = vm_states.ACTIVE
                updates = {'vm_state': vm_state, 'task_state': None}
                self._set_vm_state_and_notify(context, instance.uuid,
                                              'migrate_server',
                                              updates, ex, legacy_spec)
        except Exception as ex:
            with excutils.save_and_reraise_exception():
                updates = {'vm_state': instance.vm_state,
                           'task_state': None}
                self._set_vm_state_and_notify(context, instance.uuid,
                                              'migrate_server',
                                              updates, ex, legacy_spec)
        # NOTE(sbauza): Make sure we persist the new flavor in case we had
        # a successful scheduler call if and only if nothing bad happened
        if request_spec.obj_what_changed():
            request_spec.save()

    def _set_vm_state_and_notify(self, context, instance_uuid, method, updates,
                                 ex, request_spec):
        scheduler_utils.set_vm_state_and_notify(
                context, instance_uuid, 'compute_task', method, updates,
                ex, request_spec)

    def _cleanup_allocated_networks(
            self, context, instance, requested_networks):
        try:
            # If we were told not to allocate networks let's save ourselves
            # the trouble of calling the network API.
            if not (requested_networks and requested_networks.no_allocate):
                self.network_api.deallocate_for_instance(
                    context, instance, requested_networks=requested_networks)
        except Exception:
            msg = _LE('Failed to deallocate networks')
            LOG.exception(msg, instance=instance)
            return

        instance.system_metadata['network_allocated'] = 'False'
        try:
            instance.save()
        except exception.InstanceNotFound:
            # NOTE: It's possible that we're cleaning up the networks
            # because the instance was deleted.  If that's the case then this
            # exception will be raised by instance.save()
            pass

    @wrap_instance_event(prefix='conductor')
    def live_migrate_instance(self, context, instance, scheduler_hint,
                              block_migration, disk_over_commit, request_spec):
        self._live_migrate(context, instance, scheduler_hint,
                           block_migration, disk_over_commit, request_spec)

    def _live_migrate(self, context, instance, scheduler_hint,
                      block_migration, disk_over_commit, request_spec):
        destination = scheduler_hint.get("host")

        def _set_vm_state(context, instance, ex, vm_state=None,
                          task_state=None):
            request_spec = {'instance_properties': {
                'uuid': instance.uuid, },
            }
            scheduler_utils.set_vm_state_and_notify(context,
                instance.uuid,
                'compute_task', 'migrate_server',
                dict(vm_state=vm_state,
                     task_state=task_state,
                     expected_task_state=task_states.MIGRATING,),
                ex, request_spec)

        migration = objects.Migration(context=context.elevated())
        migration.dest_compute = destination
        migration.status = 'accepted'
        migration.instance_uuid = instance.uuid
        migration.source_compute = instance.host
        migration.migration_type = 'live-migration'
        if instance.obj_attr_is_set('flavor'):
            migration.old_instance_type_id = instance.flavor.id
            migration.new_instance_type_id = instance.flavor.id
        else:
            migration.old_instance_type_id = instance.instance_type_id
            migration.new_instance_type_id = instance.instance_type_id
        migration.create()

        task = self._build_live_migrate_task(context, instance, destination,
                                             block_migration, disk_over_commit,
                                             migration, request_spec)
        try:
            task.execute()
        except (exception.NoValidHost,
                exception.ComputeHostNotFound,
                exception.ComputeServiceUnavailable,
                exception.InvalidHypervisorType,
                exception.InvalidCPUInfo,
                exception.UnableToMigrateToSelf,
                exception.DestinationHypervisorTooOld,
                exception.InvalidLocalStorage,
                exception.InvalidSharedStorage,
                exception.HypervisorUnavailable,
                exception.InstanceInvalidState,
                exception.MigrationPreCheckError,
                exception.MigrationPreCheckClientException,
                exception.LiveMigrationWithOldNovaNotSupported,
                exception.MigrationSchedulerRPCError) as ex:
            with excutils.save_and_reraise_exception():
                # TODO(johngarbutt) - eventually need instance actions here
                _set_vm_state(context, instance, ex, instance.vm_state)
                migration.status = 'error'
                migration.save()
        except Exception as ex:
            LOG.error(_LE('Migration of instance %(instance_id)s to host'
                          ' %(dest)s unexpectedly failed.'),
                      {'instance_id': instance.uuid, 'dest': destination},
                      exc_info=True)
            _set_vm_state(context, instance, ex, vm_states.ERROR,
                          instance.task_state)
            migration.status = 'error'
            migration.save()
            raise exception.MigrationError(reason=six.text_type(ex))

    def _build_live_migrate_task(self, context, instance, destination,
                                 block_migration, disk_over_commit, migration,
                                 request_spec=None):
        return live_migrate.LiveMigrationTask(context, instance,
                                              destination, block_migration,
                                              disk_over_commit, migration,
                                              self.compute_rpcapi,
                                              self.servicegroup_api,
                                              self.scheduler_client,
                                              request_spec)

    def _build_cold_migrate_task(self, context, instance, flavor,
                                 request_spec, reservations,
                                 clean_shutdown):
        return migrate.MigrationTask(context, instance, flavor,
                                     request_spec,
                                     reservations, clean_shutdown,
                                     self.compute_rpcapi,
                                     self.scheduler_client)

    def _destroy_build_request(self, context, instance):
        # The BuildRequest needs to be stored until the instance is mapped to
        # an instance table. At that point it will never be used again and
        # should be deleted.
        try:
            build_request = objects.BuildRequest.get_by_instance_uuid(context,
                    instance.uuid)
            # TODO(alaski): Sync API updates of the build_request to the
            # instance before it is destroyed. Right now only locked_by can
            # be updated before this is destroyed.
            build_request.destroy()
        except exception.BuildRequestNotFound:
            with excutils.save_and_reraise_exception() as exc_ctxt:
                service_version = objects.Service.get_minimum_version(
                    context, 'nova-osapi_compute')
                if service_version >= 12:
                    # A BuildRequest was created during the boot process, the
                    # NotFound exception indicates a delete happened which
                    # should abort the boot.
                    pass
                else:
                    LOG.debug('BuildRequest not found for instance %(uuid)s, '
                              'likely due to an older nova-api service '
                              'running.', {'uuid': instance.uuid})
                    exc_ctxt.reraise = False
            return

    def _populate_instance_mapping(self, context, instance, host):
        try:
            inst_mapping = objects.InstanceMapping.get_by_instance_uuid(
                    context, instance.uuid)
        except exception.InstanceMappingNotFound:
            # NOTE(alaski): If nova-api is up to date this exception should
            # never be hit. But during an upgrade it's possible that an old
            # nova-api didn't create an instance_mapping during this boot
            # request.
            LOG.debug('Instance was not mapped to a cell, likely due '
                      'to an older nova-api service running.',
                      instance=instance)
            return None
        else:
            try:
                host_mapping = objects.HostMapping.get_by_host(context,
                        host['host'])
            except exception.HostMappingNotFound:
                # NOTE(alaski): For now this exception means that a
                # deployment has not migrated to cellsv2 and we should
                # remove the instance_mapping that has been created.
                # Eventually this will indicate a failure to properly map a
                # host to a cell and we may want to reschedule.
                inst_mapping.destroy()
                return None
            else:
                inst_mapping.cell_mapping = host_mapping.cell_mapping
                inst_mapping.save()
        return inst_mapping

    def build_instances(self, context, instances, image, filter_properties,
            admin_password, injected_files, requested_networks,
            security_groups, block_device_mapping=None, legacy_bdm=True):
        # TODO(ndipanov): Remove block_device_mapping and legacy_bdm in version
        #                 2.0 of the RPC API.
        # TODO(danms): Remove this in version 2.0 of the RPC API
        if (requested_networks and
                not isinstance(requested_networks,
                               objects.NetworkRequestList)):
            requested_networks = objects.NetworkRequestList.from_tuples(
                requested_networks)
        # TODO(melwitt): Remove this in version 2.0 of the RPC API
        flavor = filter_properties.get('instance_type')
        if flavor and not isinstance(flavor, objects.Flavor):
            # Code downstream may expect extra_specs to be populated since it
            # is receiving an object, so lookup the flavor to ensure this.
            flavor = objects.Flavor.get_by_id(context, flavor['id'])
            filter_properties = dict(filter_properties, instance_type=flavor)

        request_spec = {}
        try:
            # check retry policy. Rather ugly use of instances[0]...
            # but if we've exceeded max retries... then we really only
            # have a single instance.
            scheduler_utils.populate_retry(
                filter_properties, instances[0].uuid)
            request_spec = scheduler_utils.build_request_spec(
                    context, image, instances)
            hosts = self._schedule_instances(
                    context, request_spec, filter_properties)
        except Exception as exc:
            updates = {'vm_state': vm_states.ERROR, 'task_state': None}
            for instance in instances:
                self._set_vm_state_and_notify(
                    context, instance.uuid, 'build_instances', updates,
                    exc, request_spec)
                try:
                    # If the BuildRequest stays around then instance show/lists
                    # will pull from it rather than the errored instance.
                    self._destroy_build_request(context, instance)
                except exception.BuildRequestNotFound:
                    pass
                self._cleanup_allocated_networks(
                    context, instance, requested_networks)
            return

        for (instance, host) in six.moves.zip(instances, hosts):
            try:
                instance.refresh()
            except (exception.InstanceNotFound,
                    exception.InstanceInfoCacheNotFound):
                LOG.debug('Instance deleted during build', instance=instance)
                continue
            local_filter_props = copy.deepcopy(filter_properties)
            scheduler_utils.populate_filter_properties(local_filter_props,
                host)
            # The block_device_mapping passed from the api doesn't contain
            # instance specific information
            bdms = objects.BlockDeviceMappingList.get_by_instance_uuid(
                    context, instance.uuid)

            # This is populated in scheduler_utils.populate_retry
            num_attempts = local_filter_props.get('retry',
                                                  {}).get('num_attempts', 1)
            if num_attempts <= 1:
                # If this is a reschedule the instance is already mapped to
                # this cell and the BuildRequest is already deleted so ignore
                # the logic below.
                inst_mapping = self._populate_instance_mapping(context,
                                                               instance,
                                                               host)
                try:
                    self._destroy_build_request(context, instance)
                except exception.BuildRequestNotFound:
                    # This indicates an instance delete has been requested in
                    # the API. Stop the build, cleanup the instance_mapping and
                    # potentially the block_device_mappings
                    # TODO(alaski): Handle block_device_mapping cleanup
                    if inst_mapping:
                        inst_mapping.destroy()
                    return

            self.compute_rpcapi.build_and_run_instance(context,
                    instance=instance, host=host['host'], image=image,
                    request_spec=request_spec,
                    filter_properties=local_filter_props,
                    admin_password=admin_password,
                    injected_files=injected_files,
                    requested_networks=requested_networks,
                    security_groups=security_groups,
                    block_device_mapping=bdms, node=host['nodename'],
                    limits=host['limits'])

    def _schedule_instances(self, context, request_spec, filter_properties):
        scheduler_utils.setup_instance_group(context, request_spec,
                                             filter_properties)
        # TODO(sbauza): Hydrate here the object until we modify the
        # scheduler.utils methods to directly use the RequestSpec object
        spec_obj = objects.RequestSpec.from_primitives(
            context, request_spec, filter_properties)
        hosts = self.scheduler_client.select_destinations(context, spec_obj)
        return hosts

    def unshelve_instance(self, context, instance, request_spec=None):
        sys_meta = instance.system_metadata

        def safe_image_show(ctx, image_id):
            if image_id:
                return self.image_api.get(ctx, image_id, show_deleted=False)
            else:
                raise exception.ImageNotFound(image_id='')

        if instance.vm_state == vm_states.SHELVED:
            instance.task_state = task_states.POWERING_ON
            instance.save(expected_task_state=task_states.UNSHELVING)
            self.compute_rpcapi.start_instance(context, instance)
        elif instance.vm_state == vm_states.SHELVED_OFFLOADED:
            image = None
            image_id = sys_meta.get('shelved_image_id')
            # No need to check for image if image_id is None as
            # "shelved_image_id" key is not set for volume backed
            # instance during the shelve process
            if image_id:
                with compute_utils.EventReporter(
                    context, 'get_image_info', instance.uuid):
                    try:
                        image = safe_image_show(context, image_id)
                    except exception.ImageNotFound:
                        instance.vm_state = vm_states.ERROR
                        instance.save()

                        reason = _('Unshelve attempted but the image %s '
                                   'cannot be found.') % image_id

                        LOG.error(reason, instance=instance)
                        raise exception.UnshelveException(
                            instance_id=instance.uuid, reason=reason)

            try:
                with compute_utils.EventReporter(context, 'schedule_instances',
                                                 instance.uuid):
                    if not request_spec:
                        # NOTE(sbauza): We were unable to find an original
                        # RequestSpec object - probably because the instance is
                        # old. We need to mock that the old way
                        filter_properties = {}
                        request_spec = scheduler_utils.build_request_spec(
                            context, image, [instance])
                    else:
                        # NOTE(sbauza): Force_hosts/nodes needs to be reset
                        # if we want to make sure that the next destination
                        # is not forced to be the original host
                        request_spec.reset_forced_destinations()
                        # TODO(sbauza): Provide directly the RequestSpec object
                        # when _schedule_instances(),
                        # populate_filter_properties and populate_retry()
                        # accept it
                        filter_properties = request_spec.\
                            to_legacy_filter_properties_dict()
                        request_spec = request_spec.\
                            to_legacy_request_spec_dict()
                    scheduler_utils.populate_retry(filter_properties,
                                                   instance.uuid)
                    hosts = self._schedule_instances(
                            context, request_spec, filter_properties)
                    host_state = hosts[0]
                    scheduler_utils.populate_filter_properties(
                            filter_properties, host_state)
                    (host, node) = (host_state['host'], host_state['nodename'])
                    self.compute_rpcapi.unshelve_instance(
                            context, instance, host, image=image,
                            filter_properties=filter_properties, node=node)
            except (exception.NoValidHost,
                    exception.UnsupportedPolicyException):
                instance.task_state = None
                instance.save()
                LOG.warning(_LW("No valid host found for unshelve instance"),
                            instance=instance)
                return
            except Exception:
                with excutils.save_and_reraise_exception():
                    instance.task_state = None
                    instance.save()
                    LOG.error(_LE("Unshelve attempted but an error "
                                  "has occurred"), instance=instance)
        else:
            LOG.error(_LE('Unshelve attempted but vm_state not SHELVED or '
                          'SHELVED_OFFLOADED'), instance=instance)
            instance.vm_state = vm_states.ERROR
            instance.save()
            return

    def rebuild_instance(self, context, instance, orig_image_ref, image_ref,
                         injected_files, new_pass, orig_sys_metadata,
                         bdms, recreate, on_shared_storage,
                         preserve_ephemeral=False, host=None,
                         request_spec=None):

        with compute_utils.EventReporter(context, 'rebuild_server',
                                          instance.uuid):
            node = limits = None
            if not host:
                if not request_spec:
                    # NOTE(sbauza): We were unable to find an original
                    # RequestSpec object - probably because the instance is old
                    # We need to mock that the old way
                    filter_properties = {'ignore_hosts': [instance.host]}
                    request_spec = scheduler_utils.build_request_spec(
                            context, image_ref, [instance])
                else:
                    # NOTE(sbauza): Augment the RequestSpec object by excluding
                    # the source host for avoiding the scheduler to pick it
                    request_spec.ignore_hosts = request_spec.ignore_hosts or []
                    request_spec.ignore_hosts.append(instance.host)
                    # NOTE(sbauza): Force_hosts/nodes needs to be reset
                    # if we want to make sure that the next destination
                    # is not forced to be the original host
                    request_spec.reset_forced_destinations()
                    # TODO(sbauza): Provide directly the RequestSpec object
                    # when _schedule_instances() and _set_vm_state_and_notify()
                    # accept it
                    filter_properties = request_spec.\
                        to_legacy_filter_properties_dict()
                    request_spec = request_spec.to_legacy_request_spec_dict()
                try:
                    hosts = self._schedule_instances(
                            context, request_spec, filter_properties)
                    host_dict = hosts.pop(0)
                    host, node, limits = (host_dict['host'],
                                          host_dict['nodename'],
                                          host_dict['limits'])
                except exception.NoValidHost as ex:
                    with excutils.save_and_reraise_exception():
                        self._set_vm_state_and_notify(context, instance.uuid,
                                'rebuild_server',
                                {'vm_state': instance.vm_state,
                                 'task_state': None}, ex, request_spec)
                        LOG.warning(_LW("No valid host found for rebuild"),
                                    instance=instance)
                except exception.UnsupportedPolicyException as ex:
                    with excutils.save_and_reraise_exception():
                        self._set_vm_state_and_notify(context, instance.uuid,
                                'rebuild_server',
                                {'vm_state': instance.vm_state,
                                 'task_state': None}, ex, request_spec)
                        LOG.warning(_LW("Server with unsupported policy "
                                        "cannot be rebuilt"),
                                    instance=instance)

            try:
                migration = objects.Migration.get_by_instance_and_status(
                    context, instance.uuid, 'accepted')
            except exception.MigrationNotFoundByStatus:
                LOG.debug("No migration record for the rebuild/evacuate "
                          "request.", instance=instance)
                migration = None

            compute_utils.notify_about_instance_usage(
                self.notifier, context, instance, "rebuild.scheduled")

            self.compute_rpcapi.rebuild_instance(context,
                    instance=instance,
                    new_pass=new_pass,
                    injected_files=injected_files,
                    image_ref=image_ref,
                    orig_image_ref=orig_image_ref,
                    orig_sys_metadata=orig_sys_metadata,
                    bdms=bdms,
                    recreate=recreate,
                    on_shared_storage=on_shared_storage,
                    preserve_ephemeral=preserve_ephemeral,
                    migration=migration,
                    host=host, node=node, limits=limits)