blueprint host-aggregates: OSAPI/virt integration, via nova.compute.api

This commit introduces the first cut of integration between the OSAPI
Admin extensions for host aggregates and the virt layer.

This is part of a series of commits that have started with change:

https://review.openstack.org/#change,3035

Change-Id: I75d8b616e3b8f8cef75d40d937e0dce9f29b16db

nova/compute/aggregate_states.py

@@ -17,12 +17,28 @@
 
 """Possible states for host aggregates.
 
-An aggregate may be 'building', in which case the admin has triggered its
+An aggregate may be 'created', in which case the admin has triggered its
-creation, but the underlying hypervisor pool has not actually being created
+creation, but the underlying hypervisor pool has not actually being set up
-yet. An aggregate may be 'active', in which case the underlying hypervisor
+yet. An aggregate may be 'changing', meaning that the underlying hypervisor
-pool is up and running. An aggregate may be in 'error' in all other cases.
+pool is being setup. An aggregate may be 'active', in which case the underlying
+hypervisor pool is up and running. An aggregate may be 'dismissed' when it has
+no hosts and it has been deleted. An aggregate may be in 'error' in all other
+cases.
+A 'created' aggregate becomes 'changing' during the first request of
+adding a host. During a 'changing' status no other requests will be accepted;
+this is to allow the hypervisor layer to instantiate the underlying pool
+without any potential race condition that may incur in master/slave-based
+configurations. The aggregate goes into the 'active' state when the underlying
+pool has been correctly instantiated.
+All other operations (e.g. add/remove hosts) that succeed will keep the
+aggregate in the 'active' state. If a number of continuous requests fail,
+an 'active' aggregate goes into an 'error' state. To recover from such a state,
+admin intervention is required. Currently an error state is irreversible,
+that is, in order to recover from it an aggregate must be deleted.
 """
 
-BUILDING = 'building'
+CREATED = 'created'
+CHANGING = 'changing'
 ACTIVE = 'active'
 ERROR = 'error'
+DISMISSED = 'dismissed'

nova/db/sqlalchemy/api.py

@@ -4257,7 +4257,7 @@ def aggregate_create(context, values, metadata=None):
     try:
         aggregate = models.Aggregate()
         aggregate.update(values)
-        aggregate.operational_state = aggregate_states.BUILDING
+        aggregate.operational_state = aggregate_states.CREATED
         aggregate.save()
     except exception.DBError:
         raise exception.AggregateNameExists(aggregate_name=values['name'])
@@ -4435,20 +4435,27 @@ def aggregate_host_delete(context, aggregate_id, host):
 @require_admin_context
 @require_aggregate_exists
 def aggregate_host_add(context, aggregate_id, host):
+    session = get_session()
     host_ref = _aggregate_get_query(context,
                                     models.AggregateHost,
                                     models.AggregateHost.aggregate_id,
                                     aggregate_id,
-                                    read_deleted='no').\
+                                    session=session,
+                                    read_deleted='yes').\
                                     filter_by(host=host).first()
     if not host_ref:
         try:
             host_ref = models.AggregateHost()
             values = {"host": host, "aggregate_id": aggregate_id, }
             host_ref.update(values)
-            host_ref.save()
+            host_ref.save(session=session)
         except exception.DBError:
             raise exception.AggregateHostConflict(host=host)
+    elif host_ref.deleted:
+        host_ref.update({'deleted': False,
+                         'deleted_at': None,
+                         'updated_at': literal_column('updated_at')})
+        host_ref.save(session=session)
     else:
         raise exception.AggregateHostExists(host=host,
                                             aggregate_id=aggregate_id)