mirror nova host aggregate members to placement

This patch is the first step in syncing the nova host aggregate
information with the placement service. The scheduler report client gets
a couple new public methods -- aggregate_add_host() and
aggregate_remove_host(). Both of these methods do **NOT** impact the
provider tree cache that the scheduler reportclient keeps when
instantiated inside the compute resource tracker.

Instead, these two new reportclient methods look up a resource provider
by *name* (not UUID) since that is what is supplied by the
os-aggregates Compute API when adding or removing a "host" to/from a
nova host aggregate.

Change-Id: Ibd7aa4f8c4ea787774becece324d9051521c44b6
blueprint: placement-mirror-host-aggregates

doc/source/user/placement.rst

@@ -293,10 +293,11 @@ Rocky (18.0.0)
   that service. This is because the ``nova-api`` service now needs to talk
   to the placement service in order to (1) delete resource provider allocations
   when deleting an instance and the ``nova-compute`` service on which that
-  instance is running is down and (2) delete a ``nova-compute`` service record
-  via the ``DELETE /os-services/{service_id}`` API. This change is idempotent
-  if ``[placement]`` is not configured in ``nova-api`` but it will result in
-  new warnings in the logs until configured.
+  instance is running is down (2) delete a ``nova-compute`` service record via
+  the ``DELETE /os-services/{service_id}`` API and (3) mirror aggregate host
+  associations to the placement service. This change is idempotent if
+  ``[placement]`` is not configured in ``nova-api`` but it will result in new
+  warnings in the logs until configured.
 
 REST API
 ========

nova/tests/functional/test_aggregates.py

@@ -141,20 +141,11 @@ class AggregateRequestFiltersTest(test.TestCase,
 
         host_uuid = self._get_provider_uuid_by_host(host)
 
-        # Get the existing aggregates for this host in placement and add the
-        # new one to it
-        aggs = self.report_client.get(
-            '/resource_providers/%s/aggregates' % host_uuid,
-            version='1.1').json()
-        placement_aggs = aggs['aggregates']
-        placement_aggs.append(agg['uuid'])
-
         # Make sure we have a view of the provider we're about to mess with
         # FIXME(efried): This should be a thing we can do without internals
-        self.report_client._ensure_resource_provider(self.context, host_uuid)
-
-        self.report_client.set_aggregates_for_provider(self.context, host_uuid,
-                                                       placement_aggs)
+        self.report_client._ensure_resource_provider(
+            self.context, host_uuid, name=host)
+        self.report_client.aggregate_add_host(self.context, agg['uuid'], host)
 
     def _wait_for_state_change(self, server, from_status):
         for i in range(0, 50):

releasenotes/notes/mirror-host-aggregates-to-placement-597473efa94ee558.yaml

@@ -0,0 +1,21 @@
+---
+features:
+  - |
+    We now attempt to mirror the association of compute host to host aggregate
+    into the placement API. When administrators use the ``POST
+    /os-aggregates/{aggregate_id}/action`` Compute API call to add or remove a
+    host from an aggregate, the nova-api service will attempt to ensure that a
+    corresponding record is created in the placement API for the resource
+    provider (compute host) and host aggregate UUID.
+
+    The nova-api service needs to understand how to connect to the placement
+    service in order for this mirroring process to work. Administrators should
+    ensure that there is a ``[placement]`` section in the nova.conf file which
+    is used by the nova-api service, and that credentials for interacting with
+    placement are contained in that section.
+
+    If the ``[placement]`` section is missing from the nova-api's nova.conf
+    file, nothing will break however there will be some warnings generated in
+    the nova-api's log file when administrators associate a compute host with a
+    host aggregate. However, this will become a failure starting in the 19.0.0
+    Stein release.