Allow unshelve to a specific host (Compute API part)

This patch introduce changes to the compute API that will allow
PROJECT_ADMIN to unshelve an shelved offloaded server to a specific host.
This patch also supports the ability to unpin the availability_zone of an
instance that is bound to it.

Implements: blueprint unshelve-to-host
Change-Id: Ieb4766fdd88c469574fad823e05fe401537cdc30

nova/api/openstack/compute/shelve.py

@@ -95,14 +95,15 @@ def _unshelve(self, req, id, body):
         context.can(shelve_policies.POLICY_ROOT % 'unshelve',
                     target={'project_id': instance.project_id})
 
-        new_az = None
+        unshelve_args = {}
+
         unshelve_dict = body['unshelve']
         support_az = api_version_request.is_supported(req, '2.77')
         if support_az and unshelve_dict:
-            new_az = unshelve_dict['availability_zone']
+            unshelve_args['new_az'] = unshelve_dict['availability_zone']
 
         try:
-            self.compute_api.unshelve(context, instance, new_az=new_az)
+            self.compute_api.unshelve(context, instance, **unshelve_args)
         except (exception.InstanceIsLocked,
                 exception.UnshelveInstanceInvalidState,
                 exception.MismatchVolumeAZException) as e:

nova/compute/api.py

@@ -380,6 +380,8 @@ def inner(self, context, instance, *args, **kwargs):
 class API:
     """API for interacting with the compute manager."""
 
+    _sentinel = object()
+
     def __init__(self, image_api=None, network_api=None, volume_api=None):
         self.image_api = image_api or glance.API()
         self.network_api = network_api or neutron.API()
@@ -4391,31 +4393,45 @@ def shelve_offload(self, context, instance, clean_shutdown=True):
             context, instance=instance,
             clean_shutdown=clean_shutdown, accel_uuids=accel_uuids)
 
+    def _check_offloaded(self, context, instance):
+        """Check if the status of an instance is SHELVE_OFFLOADED,
+        if not raise an exception.
+        """
+        if instance.vm_state != vm_states.SHELVED_OFFLOADED:
+            # NOTE(brinzhang): If the server status is 'SHELVED', it still
+            # belongs to a host, the availability_zone should not change.
+            # Unshelving a shelved offloaded server will go through the
+            # scheduler to find a new host.
+            raise exception.UnshelveInstanceInvalidState(
+                state=instance.vm_state, instance_uuid=instance.uuid)
+
+    def _ensure_host_in_az(self, context, host, availability_zone):
+        """Ensure the host provided belongs to the availability zone,
+        if not raise an exception.
+        """
+        if availability_zone is not None:
+            host_az = availability_zones.get_host_availability_zone(
+                context,
+                host
+            )
+            if host_az != availability_zone:
+                raise exception.UnshelveHostNotInAZ(
+                    host=host, availability_zone=availability_zone)
+
     def _validate_unshelve_az(self, context, instance, availability_zone):
         """Verify the specified availability_zone during unshelve.
 
-        Verifies that the server is shelved offloaded, the AZ exists and
-        if [cinder]/cross_az_attach=False, that any attached volumes are in
-        the same AZ.
+        Verifies the AZ exists and if [cinder]/cross_az_attach=False, that
+        any attached volumes are in the same AZ.
 
         :param context: nova auth RequestContext for the unshelve action
         :param instance: Instance object for the server being unshelved
         :param availability_zone: The user-requested availability zone in
             which to unshelve the server.
-        :raises: UnshelveInstanceInvalidState if the server is not shelved
-            offloaded
         :raises: InvalidRequest if the requested AZ does not exist
         :raises: MismatchVolumeAZException if [cinder]/cross_az_attach=False
             and any attached volumes are not in the requested AZ
         """
-        if instance.vm_state != vm_states.SHELVED_OFFLOADED:
-            # NOTE(brinzhang): If the server status is 'SHELVED', it still
-            # belongs to a host, the availability_zone has not changed.
-            # Unshelving a shelved offloaded server will go through the
-            # scheduler to find a new host.
-            raise exception.UnshelveInstanceInvalidState(
-                state=instance.vm_state, instance_uuid=instance.uuid)
-
         available_zones = availability_zones.get_availability_zones(
             context, self.host_api, get_only_available=True)
         if availability_zone not in available_zones:
@@ -4443,31 +4459,88 @@ def _validate_unshelve_az(self, context, instance, availability_zone):
 
     @block_extended_resource_request
     @check_instance_lock
-    @check_instance_state(vm_state=[vm_states.SHELVED,
-        vm_states.SHELVED_OFFLOADED])
-    def unshelve(self, context, instance, new_az=None):
-        """Restore a shelved instance."""
+    @check_instance_state(
+            vm_state=[vm_states.SHELVED, vm_states.SHELVED_OFFLOADED])
+    def unshelve(
+            self, context, instance, new_az=_sentinel, host=None):
+        """Restore a shelved instance.
+
+        :param context: the nova request context
+        :param instance: nova.objects.instance.Instance object
+        :param new_az: (optional) target AZ.
+                       If None is provided then the current AZ restriction
+                       will be removed from the instance.
+                       If the parameter is not provided then the current
+                       AZ restriction will not be changed.
+        :param host: (optional) a host to target
+        """
+        # Unshelving a shelved offloaded server will go through the
+        # scheduler to pick a new host, so we update the
+        # RequestSpec.availability_zone here. Note that if scheduling
+        # fails the RequestSpec will remain updated, which is not great.
+        # Bug open to track this https://bugs.launchpad.net/nova/+bug/1978573
+
+        az_passed = new_az is not self._sentinel
+
         request_spec = objects.RequestSpec.get_by_instance_uuid(
             context, instance.uuid)
 
-        if new_az:
+        # We need to check a list of preconditions and validate inputs first
+
+        # Ensure instance is shelve offloaded
+        if az_passed or host:
+            self._check_offloaded(context, instance)
+
+        if az_passed and new_az:
+            # we have to ensure that new AZ is valid
             self._validate_unshelve_az(context, instance, new_az)
-            LOG.debug("Replace the old AZ %(old_az)s in RequestSpec "
-                      "with a new AZ %(new_az)s of the instance.",
-                      {"old_az": request_spec.availability_zone,
-                       "new_az": new_az}, instance=instance)
-            # Unshelving a shelved offloaded server will go through the
-            # scheduler to pick a new host, so we update the
-            # RequestSpec.availability_zone here. Note that if scheduling
-            # fails the RequestSpec will remain updated, which is not great,
-            # but if we want to change that we need to defer updating the
-            # RequestSpec until conductor which probably means RPC changes to
-            # pass the new_az variable to conductor. This is likely low
-            # priority since the RequestSpec.availability_zone on a shelved
-            # offloaded server does not mean much anyway and clearly the user
-            # is trying to put the server in the target AZ.
-            request_spec.availability_zone = new_az
-            request_spec.save()
+        # This will be the AZ of the instance after the unshelve. It can be
+        # None indicating that the instance is not pinned to any AZ after the
+        # unshelve
+        expected_az_after_unshelve = (
+            request_spec.availability_zone
+            if not az_passed else new_az
+        )
+        # host is requested, so we have to see if it exists and does not
+        # contradict with the AZ of the instance
+        if host:
+            # Ensure that the requested host exists otherwise raise
+            # a ComputeHostNotFound exception
+            objects.ComputeNode.get_first_node_by_host_for_old_compat(
+                context, host, use_slave=True)
+            # A specific host is requested so we need to make sure that it is
+            # not contradicts with the AZ of the instance
+            self._ensure_host_in_az(
+                context, host, expected_az_after_unshelve)
+
+        if new_az is None:
+            LOG.debug(
+                'Unpin instance from AZ "%(old_az)s".',
+                {'old_az': request_spec.availability_zone},
+                instance=instance
+            )
+
+        LOG.debug(
+            'Unshelving instance with old availability_zone "%(old_az)s" to '
+            'new availability_zone "%(new_az)s" and host "%(host)s".',
+            {
+                'old_az': request_spec.availability_zone,
+                'new_az': '%s' %
+                          new_az if az_passed
+                                 else 'not provided',
+                'host': host,
+             },
+            instance=instance,
+        )
+        # OK every precondition checks out, we just need to tell the scheduler
+        # where to put the instance
+        # We have the expected AZ already calculated. So we just need to
+        # set it in the request_spec to drive the scheduling
+        request_spec.availability_zone = expected_az_after_unshelve
+        # if host is requested we also need to tell the scheduler that
+        if host:
+            request_spec.requested_destination = objects.Destination(host=host)
+        request_spec.save()
 
         instance.task_state = task_states.UNSHELVING
         instance.save(expected_task_state=[None])

nova/conductor/manager.py

@@ -1022,6 +1022,12 @@ def safe_image_show(ctx, image_id):
                     scheduler_utils.populate_filter_properties(
                             filter_properties, selection)
                     (host, node) = (selection.service_host, selection.nodename)
+                    LOG.debug(
+                        "Scheduler selected host: %s, node:%s",
+                        host,
+                        node,
+                        instance=instance
+                    )
                     instance.availability_zone = (
                         availability_zones.get_host_availability_zone(
                             context, host))

nova/exception.py

@@ -1676,9 +1676,15 @@ class MismatchVolumeAZException(Invalid):
 
 
 class UnshelveInstanceInvalidState(InstanceInvalidState):
-    msg_fmt = _('Specifying an availability zone when unshelving server '
-                '%(instance_uuid)s with status "%(state)s" is not supported. '
-                'The server status must be SHELVED_OFFLOADED.')
+    msg_fmt = _('Specifying an availability zone or a host when unshelving '
+                'server "%(instance_uuid)s" with status "%(state)s" is not '
+                'supported. The server status must be SHELVED_OFFLOADED.')
+    code = 409
+
+
+class UnshelveHostNotInAZ(Invalid):
+    msg_fmt = _('Host "%(host)s" is not in the availability zone '
+                '"%(availability_zone)s".')
     code = 409
 
 

nova/tests/unit/api/openstack/compute/test_shelve.py

@@ -140,7 +140,9 @@ def test_unshelve_with_az_pre_2_77_failed(self, mock_get_instance):
                                'unshelve') as mock_unshelve:
             self.controller._unshelve(self.req, fakes.FAKE_UUID, body=body)
         mock_unshelve.assert_called_once_with(
-            self.req.environ['nova.context'], instance, new_az=None)
+            self.req.environ['nova.context'],
+            instance,
+        )
 
     @mock.patch('nova.compute.api.API.unshelve')
     @mock.patch('nova.api.openstack.common.get_instance')
@@ -158,7 +160,9 @@ def test_unshelve_with_none_pre_2_77_success(
                 APIVersionRequest('2.76'))
         self.controller._unshelve(self.req, fakes.FAKE_UUID, body=body)
         mock_unshelve.assert_called_once_with(
-            self.req.environ['nova.context'], instance, new_az=None)
+            self.req.environ['nova.context'],
+            instance,
+        )
 
     @mock.patch('nova.compute.api.API.unshelve')
     @mock.patch('nova.api.openstack.common.get_instance')