diff --git a/nova/api/openstack/placement/handlers/aggregate.py b/nova/api/openstack/placement/handlers/aggregate.py
index 3fec87ddbed0..382f190477f5 100644
--- a/nova/api/openstack/placement/handlers/aggregate.py
+++ b/nova/api/openstack/placement/handlers/aggregate.py
@@ -13,6 +13,7 @@
 
 from oslo_serialization import jsonutils
 from oslo_utils import encodeutils
+from oslo_utils import timeutils
 
 from nova.api.openstack.placement import microversion
 from nova.api.openstack.placement import util
@@ -30,11 +31,20 @@ PUT_AGGREGATES_SCHEMA = {
 }
 
 
-def _send_aggregates(response, aggregate_uuids):
+def _send_aggregates(req, aggregate_uuids):
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
+    response = req.response
     response.status = 200
     response.body = encodeutils.to_utf8(
         jsonutils.dumps(_serialize_aggregates(aggregate_uuids)))
     response.content_type = 'application/json'
+    if want_version.matches((1, 15)):
+        req.response.cache_control = 'no-cache'
+        # We never get an aggregate itself, we get the list of aggregates
+        # that are associated with a resource provider. We don't record the
+        # time when that association was made and the time when an aggregate
+        # uuid was created is not relevant, so here we punt and use utcnow.
+        req.response.last_modified = timeutils.utcnow(with_timezone=True)
     return response
 
 
@@ -59,7 +69,7 @@ def get_aggregates(req):
         context, uuid)
     aggregate_uuids = resource_provider.get_aggregates()
 
-    return _send_aggregates(req.response, aggregate_uuids)
+    return _send_aggregates(req, aggregate_uuids)
 
 
 @wsgi_wrapper.PlacementWsgify
@@ -73,4 +83,4 @@ def set_aggregates(req):
     aggregate_uuids = util.extract_json(req.body, PUT_AGGREGATES_SCHEMA)
     resource_provider.set_aggregates(aggregate_uuids)
 
-    return _send_aggregates(req.response, aggregate_uuids)
+    return _send_aggregates(req, aggregate_uuids)
diff --git a/nova/api/openstack/placement/handlers/allocation.py b/nova/api/openstack/placement/handlers/allocation.py
index c06d4db05dba..bafbbdf063cf 100644
--- a/nova/api/openstack/placement/handlers/allocation.py
+++ b/nova/api/openstack/placement/handlers/allocation.py
@@ -17,6 +17,7 @@ import copy
 from oslo_log import log as logging
 from oslo_serialization import jsonutils
 from oslo_utils import encodeutils
+from oslo_utils import timeutils
 import webob
 
 from nova.api.openstack.placement import microversion
@@ -161,7 +162,16 @@ def _allocations_dict(allocations, key_fetcher, resource_provider=None,
     """Turn allocations into a dict of resources keyed by key_fetcher."""
     allocation_data = collections.defaultdict(dict)
 
+    # NOTE(cdent): The last_modified for an allocation will always be
+    # based off the created_at column because allocations are only
+    # ever inserted, never updated.
+    last_modified = None
+    # Only calculate last-modified if we are using a microversion that
+    # supports it.
+    get_last_modified = want_version and want_version.matches((1, 15))
     for allocation in allocations:
+        if get_last_modified:
+            last_modified = util.pick_last_modified(last_modified, allocation)
         key = key_fetcher(allocation)
         if 'resources' not in allocation_data[key]:
             allocation_data[key]['resources'] = {}
@@ -183,7 +193,8 @@ def _allocations_dict(allocations, key_fetcher, resource_provider=None,
             result['project_id'] = allocations[0].project_id
             result['user_id'] = allocations[0].user_id
 
-    return result
+    last_modified = last_modified or timeutils.utcnow(with_timezone=True)
+    return result, last_modified
 
 
 def _serialize_allocations_for_consumer(allocations, want_version=None):
@@ -245,6 +256,7 @@ def _serialize_allocations_for_resource_provider(allocations,
 def list_for_consumer(req):
     """List allocations associated with a consumer."""
     context = req.environ['placement.context']
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
     consumer_id = util.wsgi_path_item(req.environ, 'consumer_uuid')
     want_version = req.environ[microversion.MICROVERSION_ENVIRON]
 
@@ -254,13 +266,18 @@ def list_for_consumer(req):
     allocations = rp_obj.AllocationList.get_all_by_consumer_id(
         context, consumer_id)
 
-    allocations_json = jsonutils.dumps(
-        _serialize_allocations_for_consumer(allocations, want_version))
+    output, last_modified = _serialize_allocations_for_consumer(
+        allocations, want_version)
+    allocations_json = jsonutils.dumps(output)
 
-    req.response.status = 200
-    req.response.body = encodeutils.to_utf8(allocations_json)
-    req.response.content_type = 'application/json'
-    return req.response
+    response = req.response
+    response.status = 200
+    response.body = encodeutils.to_utf8(allocations_json)
+    response.content_type = 'application/json'
+    if want_version.matches((1, 15)):
+        response.last_modified = last_modified
+        response.cache_control = 'no-cache'
+    return response
 
 
 @wsgi_wrapper.PlacementWsgify
@@ -273,6 +290,7 @@ def list_for_resource_provider(req):
     # using a dict of dicts for the output we are potentially limiting
     # ourselves in terms of sorting and filtering.
     context = req.environ['placement.context']
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
     uuid = util.wsgi_path_item(req.environ, 'uuid')
 
     # confirm existence of resource provider so we get a reasonable
@@ -286,13 +304,18 @@ def list_for_resource_provider(req):
 
     allocs = rp_obj.AllocationList.get_all_by_resource_provider(context, rp)
 
-    allocations_json = jsonutils.dumps(
-        _serialize_allocations_for_resource_provider(allocs, rp))
+    output, last_modified = _serialize_allocations_for_resource_provider(
+        allocs, rp)
+    allocations_json = jsonutils.dumps(output)
 
-    req.response.status = 200
-    req.response.body = encodeutils.to_utf8(allocations_json)
-    req.response.content_type = 'application/json'
-    return req.response
+    response = req.response
+    response.status = 200
+    response.body = encodeutils.to_utf8(allocations_json)
+    response.content_type = 'application/json'
+    if want_version.matches((1, 15)):
+        response.last_modified = last_modified
+        response.cache_control = 'no-cache'
+    return response
 
 
 def _new_allocations(context, resource_provider_uuid, consumer_uuid,
diff --git a/nova/api/openstack/placement/handlers/allocation_candidate.py b/nova/api/openstack/placement/handlers/allocation_candidate.py
index 94b6b79e0bf4..56635f54cd84 100644
--- a/nova/api/openstack/placement/handlers/allocation_candidate.py
+++ b/nova/api/openstack/placement/handlers/allocation_candidate.py
@@ -17,6 +17,7 @@ import collections
 from oslo_log import log as logging
 from oslo_serialization import jsonutils
 from oslo_utils import encodeutils
+from oslo_utils import timeutils
 import webob
 
 from nova.api.openstack.placement import microversion
@@ -224,4 +225,7 @@ def list_allocation_candidates(req):
     json_data = jsonutils.dumps(trx_cands)
     response.body = encodeutils.to_utf8(json_data)
     response.content_type = 'application/json'
+    if want_version.matches((1, 15)):
+        response.cache_control = 'no-cache'
+        response.last_modified = timeutils.utcnow(with_timezone=True)
     return response
diff --git a/nova/api/openstack/placement/handlers/inventory.py b/nova/api/openstack/placement/handlers/inventory.py
index 3d9622053b7a..15d6b3c2097d 100644
--- a/nova/api/openstack/placement/handlers/inventory.py
+++ b/nova/api/openstack/placement/handlers/inventory.py
@@ -161,21 +161,33 @@ def _make_inventory_object(resource_provider, resource_class, **data):
     return inventory
 
 
-def _send_inventories(response, resource_provider, inventories):
+def _send_inventories(req, resource_provider, inventories):
     """Send a JSON representation of a list of inventories."""
+    response = req.response
     response.status = 200
-    response.body = encodeutils.to_utf8(jsonutils.dumps(
-        _serialize_inventories(inventories, resource_provider.generation)))
+    output, last_modified = _serialize_inventories(
+        inventories, resource_provider.generation)
+    response.body = encodeutils.to_utf8(jsonutils.dumps(output))
     response.content_type = 'application/json'
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
+    if want_version.matches((1, 15)):
+        response.last_modified = last_modified
+        response.cache_control = 'no-cache'
     return response
 
 
-def _send_inventory(response, resource_provider, inventory, status=200):
+def _send_inventory(req, resource_provider, inventory, status=200):
     """Send a JSON representation of one single inventory."""
+    response = req.response
     response.status = status
     response.body = encodeutils.to_utf8(jsonutils.dumps(_serialize_inventory(
         inventory, generation=resource_provider.generation)))
     response.content_type = 'application/json'
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
+    if want_version.matches((1, 15)):
+        modified = util.pick_last_modified(None, inventory)
+        response.last_modified = modified
+        response.cache_control = 'no-cache'
     return response
 
 
@@ -195,11 +207,13 @@ def _serialize_inventories(inventories, generation):
     inventories_by_class = {inventory.resource_class: inventory
                             for inventory in inventories}
     inventories_dict = {}
+    last_modified = None
     for resource_class, inventory in inventories_by_class.items():
+        last_modified = util.pick_last_modified(last_modified, inventory)
         inventories_dict[resource_class] = _serialize_inventory(
             inventory, generation=None)
-    return {'resource_provider_generation': generation,
-            'inventories': inventories_dict}
+    return ({'resource_provider_generation': generation,
+             'inventories': inventories_dict}, last_modified)
 
 
 @wsgi_wrapper.PlacementWsgify
@@ -238,7 +252,7 @@ def create_inventory(req):
     response = req.response
     response.location = util.inventory_url(
         req.environ, resource_provider, resource_class)
-    return _send_inventory(response, resource_provider, inventory,
+    return _send_inventory(req, resource_provider, inventory,
                            status=201)
 
 
@@ -294,7 +308,7 @@ def get_inventories(req):
 
     inv_list = rp_obj.InventoryList.get_all_by_resource_provider(context, rp)
 
-    return _send_inventories(req.response, rp, inv_list)
+    return _send_inventories(req, rp, inv_list)
 
 
 @wsgi_wrapper.PlacementWsgify
@@ -323,7 +337,7 @@ def get_inventory(req):
             _('No inventory of class %(class)s for %(rp_uuid)s') %
             {'class': resource_class, 'rp_uuid': uuid})
 
-    return _send_inventory(req.response, rp, inventory)
+    return _send_inventory(req, rp, inventory)
 
 
 @wsgi_wrapper.PlacementWsgify
@@ -383,7 +397,7 @@ def set_inventories(req):
               '%(rp_uuid)s: %(error)s') % {'rp_uuid': resource_provider.uuid,
                                           'error': exc})
 
-    return _send_inventories(req.response, resource_provider, inventories)
+    return _send_inventories(req, resource_provider, inventories)
 
 
 @wsgi_wrapper.PlacementWsgify
@@ -468,4 +482,4 @@ def update_inventory(req):
               '%(rp_uuid)s: %(error)s') % {'rp_uuid': resource_provider.uuid,
                                           'error': exc})
 
-    return _send_inventory(req.response, resource_provider, inventory)
+    return _send_inventory(req, resource_provider, inventory)
diff --git a/nova/api/openstack/placement/handlers/resource_class.py b/nova/api/openstack/placement/handlers/resource_class.py
index 99a0dc0536c8..2cbeb7d91ac4 100644
--- a/nova/api/openstack/placement/handlers/resource_class.py
+++ b/nova/api/openstack/placement/handlers/resource_class.py
@@ -15,6 +15,7 @@ import copy
 
 from oslo_serialization import jsonutils
 from oslo_utils import encodeutils
+from oslo_utils import timeutils
 import webob
 
 from nova.api.openstack.placement import microversion
@@ -56,12 +57,17 @@ def _serialize_resource_class(environ, rc):
     return data
 
 
-def _serialize_resource_classes(environ, rcs):
+def _serialize_resource_classes(environ, rcs, want_version):
     output = []
+    last_modified = None
+    get_last_modified = want_version.matches((1, 15))
     for rc in rcs:
+        if get_last_modified:
+            last_modified = util.pick_last_modified(last_modified, rc)
         data = _serialize_resource_class(environ, rc)
         output.append(data)
-    return {"resource_classes": output}
+    last_modified = last_modified or timeutils.utcnow(with_timezone=True)
+    return ({"resource_classes": output}, last_modified)
 
 
 @wsgi_wrapper.PlacementWsgify
@@ -131,6 +137,7 @@ def get_resource_class(req):
     """
     name = util.wsgi_path_item(req.environ, 'name')
     context = req.environ['placement.context']
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
     # The containing application will catch a not found here.
     rc = rp_obj.ResourceClass.get_by_name(context, name)
 
@@ -138,6 +145,13 @@ def get_resource_class(req):
         _serialize_resource_class(req.environ, rc))
     )
     req.response.content_type = 'application/json'
+    if want_version.matches((1, 15)):
+        req.response.cache_control = 'no-cache'
+        # Non-custom resource classes will return None from pick_last_modified,
+        # so the 'or' causes utcnow to be used.
+        last_modified = util.pick_last_modified(None, rc) or timeutils.utcnow(
+            with_timezone=True)
+        req.response.last_modified = last_modified
     return req.response
 
 
@@ -151,13 +165,17 @@ def list_resource_classes(req):
     a collection of resource classes.
     """
     context = req.environ['placement.context']
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
     rcs = rp_obj.ResourceClassList.get_all(context)
 
     response = req.response
-    response.body = encodeutils.to_utf8(jsonutils.dumps(
-        _serialize_resource_classes(req.environ, rcs))
-    )
+    output, last_modified = _serialize_resource_classes(
+        req.environ, rcs, want_version)
+    response.body = encodeutils.to_utf8(jsonutils.dumps(output))
     response.content_type = 'application/json'
+    if want_version.matches((1, 15)):
+        response.last_modified = last_modified
+        response.cache_control = 'no-cache'
     return response
 
 
diff --git a/nova/api/openstack/placement/handlers/resource_provider.py b/nova/api/openstack/placement/handlers/resource_provider.py
index 81ecce08638a..94eae5ca7ac0 100644
--- a/nova/api/openstack/placement/handlers/resource_provider.py
+++ b/nova/api/openstack/placement/handlers/resource_provider.py
@@ -16,6 +16,7 @@ import copy
 from oslo_db import exception as db_exc
 from oslo_serialization import jsonutils
 from oslo_utils import encodeutils
+from oslo_utils import timeutils
 from oslo_utils import uuidutils
 import webob
 
@@ -140,10 +141,15 @@ def _serialize_provider(environ, resource_provider, want_version):
 
 def _serialize_providers(environ, resource_providers, want_version):
     output = []
+    last_modified = None
+    get_last_modified = want_version.matches((1, 15))
     for provider in resource_providers:
+        if get_last_modified:
+            last_modified = util.pick_last_modified(last_modified, provider)
         provider_data = _serialize_provider(environ, provider, want_version)
         output.append(provider_data)
-    return {"resource_providers": output}
+    last_modified = last_modified or timeutils.utcnow(with_timezone=True)
+    return ({"resource_providers": output}, last_modified)
 
 
 @wsgi_wrapper.PlacementWsgify
@@ -219,6 +225,7 @@ def get_resource_provider(req):
     On success return a 200 with an application/json body representing
     the resource provider.
     """
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
     uuid = util.wsgi_path_item(req.environ, 'uuid')
     # The containing application will catch a not found here.
     context = req.environ['placement.context']
@@ -226,11 +233,15 @@ def get_resource_provider(req):
     resource_provider = rp_obj.ResourceProvider.get_by_uuid(
         context, uuid)
 
-    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
-    req.response.body = encodeutils.to_utf8(jsonutils.dumps(
+    response = req.response
+    response.body = encodeutils.to_utf8(jsonutils.dumps(
         _serialize_provider(req.environ, resource_provider, want_version)))
-    req.response.content_type = 'application/json'
-    return req.response
+    response.content_type = 'application/json'
+    if want_version.matches((1, 15)):
+        modified = util.pick_last_modified(None, resource_provider)
+        response.last_modified = modified
+        response.cache_control = 'no-cache'
+    return response
 
 
 @wsgi_wrapper.PlacementWsgify
@@ -287,9 +298,13 @@ def list_resource_providers(req):
             {'error': exc})
 
     response = req.response
-    response.body = encodeutils.to_utf8(jsonutils.dumps(
-        _serialize_providers(req.environ, resource_providers, want_version)))
+    output, last_modified = _serialize_providers(
+        req.environ, resource_providers, want_version)
+    response.body = encodeutils.to_utf8(jsonutils.dumps(output))
     response.content_type = 'application/json'
+    if want_version.matches((1, 15)):
+        response.last_modified = last_modified
+        response.cache_control = 'no-cache'
     return response
 
 
@@ -303,6 +318,7 @@ def update_resource_provider(req):
     """
     uuid = util.wsgi_path_item(req.environ, 'uuid')
     context = req.environ['placement.context']
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
 
     # The containing application will catch a not found here.
     resource_provider = rp_obj.ResourceProvider.get_by_uuid(
@@ -330,8 +346,12 @@ def update_resource_provider(req):
             _('Unable to save resource provider %(rp_uuid)s: %(error)s') %
             {'rp_uuid': uuid, 'error': exc})
 
-    req.response.body = encodeutils.to_utf8(jsonutils.dumps(
+    response = req.response
+    response.status = 200
+    response.body = encodeutils.to_utf8(jsonutils.dumps(
         _serialize_provider(req.environ, resource_provider, want_version)))
-    req.response.status = 200
-    req.response.content_type = 'application/json'
-    return req.response
+    response.content_type = 'application/json'
+    if want_version.matches((1, 15)):
+        response.last_modified = resource_provider.updated_at
+        response.cache_control = 'no-cache'
+    return response
diff --git a/nova/api/openstack/placement/handlers/root.py b/nova/api/openstack/placement/handlers/root.py
index 9b5b1bb948dc..2f9c6861f2bc 100644
--- a/nova/api/openstack/placement/handlers/root.py
+++ b/nova/api/openstack/placement/handlers/root.py
@@ -13,6 +13,7 @@
 
 from oslo_serialization import jsonutils
 from oslo_utils import encodeutils
+from oslo_utils import timeutils
 
 
 from nova.api.openstack.placement import microversion
@@ -21,6 +22,7 @@ from nova.api.openstack.placement import wsgi_wrapper
 
 @wsgi_wrapper.PlacementWsgify
 def home(req):
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
     min_version = microversion.min_version_string()
     max_version = microversion.max_version_string()
     # NOTE(cdent): As sections of the api are added, links can be
@@ -34,4 +36,7 @@ def home(req):
     version_json = jsonutils.dumps({'versions': [version_data]})
     req.response.body = encodeutils.to_utf8(version_json)
     req.response.content_type = 'application/json'
+    if want_version.matches((1, 15)):
+        req.response.cache_control = 'no-cache'
+        req.response.last_modified = timeutils.utcnow(with_timezone=True)
     return req.response
diff --git a/nova/api/openstack/placement/handlers/trait.py b/nova/api/openstack/placement/handlers/trait.py
index 50fc6b7dafd8..e5c6a38cbadc 100644
--- a/nova/api/openstack/placement/handlers/trait.py
+++ b/nova/api/openstack/placement/handlers/trait.py
@@ -16,6 +16,7 @@ import copy
 import jsonschema
 from oslo_serialization import jsonutils
 from oslo_utils import encodeutils
+from oslo_utils import timeutils
 import webob
 
 from nova.api.openstack.placement import microversion
@@ -85,14 +86,26 @@ def _normalize_traits_qs_param(qs):
     return filters
 
 
-def _serialize_traits(traits):
-    return {'traits': [trait.name for trait in traits]}
+def _serialize_traits(traits, want_version):
+    last_modified = None
+    get_last_modified = want_version.matches((1, 15))
+    trait_names = []
+    for trait in traits:
+        if get_last_modified:
+            last_modified = util.pick_last_modified(last_modified, trait)
+        trait_names.append(trait.name)
+
+    # If there were no traits, set last_modified to now
+    last_modified = last_modified or timeutils.utcnow(with_timezone=True)
+
+    return {'traits': trait_names}, last_modified
 
 
 @wsgi_wrapper.PlacementWsgify
 @microversion.version_handler('1.6')
 def put_trait(req):
     context = req.environ['placement.context']
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
     name = util.wsgi_path_item(req.environ, 'name')
 
     try:
@@ -110,10 +123,16 @@ def put_trait(req):
         trait.create()
         req.response.status = 201
     except exception.TraitExists:
+        # Get the trait that already exists to get last-modified time.
+        if want_version.matches((1, 15)):
+            trait = rp_obj.Trait.get_by_name(context, name)
         req.response.status = 204
 
     req.response.content_type = None
     req.response.location = util.trait_url(req.environ, trait)
+    if want_version.matches((1, 15)):
+        req.response.last_modified = trait.created_at
+        req.response.cache_control = 'no-cache'
     return req.response
 
 
@@ -121,16 +140,20 @@ def put_trait(req):
 @microversion.version_handler('1.6')
 def get_trait(req):
     context = req.environ['placement.context']
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
     name = util.wsgi_path_item(req.environ, 'name')
 
     try:
-        rp_obj.Trait.get_by_name(context, name)
+        trait = rp_obj.Trait.get_by_name(context, name)
     except exception.TraitNotFound as ex:
         raise webob.exc.HTTPNotFound(
             explanation=ex.format_message())
 
     req.response.status = 204
     req.response.content_type = None
+    if want_version.matches((1, 15)):
+        req.response.last_modified = trait.created_at
+        req.response.cache_control = 'no-cache'
     return req.response
 
 
@@ -163,6 +186,7 @@ def delete_trait(req):
 @util.check_accept('application/json')
 def list_traits(req):
     context = req.environ['placement.context']
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
     filters = {}
 
     try:
@@ -185,8 +209,11 @@ def list_traits(req):
 
     traits = rp_obj.TraitList.get_all(context, filters)
     req.response.status = 200
-    req.response.body = encodeutils.to_utf8(
-        jsonutils.dumps(_serialize_traits(traits)))
+    output, last_modified = _serialize_traits(traits, want_version)
+    if want_version.matches((1, 15)):
+        req.response.last_modified = last_modified
+        req.response.cache_control = 'no-cache'
+    req.response.body = encodeutils.to_utf8(jsonutils.dumps(output))
     req.response.content_type = 'application/json'
     return req.response
 
@@ -196,6 +223,7 @@ def list_traits(req):
 @util.check_accept('application/json')
 def list_traits_for_resource_provider(req):
     context = req.environ['placement.context']
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
     uuid = util.wsgi_path_item(req.environ, 'uuid')
 
     # Resource provider object is needed for two things: If it is
@@ -211,9 +239,13 @@ def list_traits_for_resource_provider(req):
              {'uuid': uuid, 'error': exc})
 
     traits = rp_obj.TraitList.get_all_by_resource_provider(context, rp)
-    response_body = _serialize_traits(traits)
+    response_body, last_modified = _serialize_traits(traits, want_version)
     response_body["resource_provider_generation"] = rp.generation
 
+    if want_version.matches((1, 15)):
+        req.response.last_modified = last_modified
+        req.response.cache_control = 'no-cache'
+
     req.response.status = 200
     req.response.body = encodeutils.to_utf8(jsonutils.dumps(response_body))
     req.response.content_type = 'application/json'
@@ -225,6 +257,7 @@ def list_traits_for_resource_provider(req):
 @util.require_content('application/json')
 def update_traits_for_resource_provider(req):
     context = req.environ['placement.context']
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
     uuid = util.wsgi_path_item(req.environ, 'uuid')
     data = util.extract_json(req.body, SET_TRAITS_FOR_RP_SCHEMA)
     rp_gen = data['resource_provider_generation']
@@ -248,9 +281,12 @@ def update_traits_for_resource_provider(req):
 
     resource_provider.set_traits(trait_objs)
 
-    response_body = _serialize_traits(trait_objs)
+    response_body, last_modified = _serialize_traits(trait_objs, want_version)
     response_body[
         'resource_provider_generation'] = resource_provider.generation
+    if want_version.matches((1, 15)):
+        req.response.last_modified = last_modified
+        req.response.cache_control = 'no-cache'
     req.response.status = 200
     req.response.body = encodeutils.to_utf8(jsonutils.dumps(response_body))
     req.response.content_type = 'application/json'
diff --git a/nova/api/openstack/placement/handlers/usage.py b/nova/api/openstack/placement/handlers/usage.py
index 6349c5352bcd..beec996ef18e 100644
--- a/nova/api/openstack/placement/handlers/usage.py
+++ b/nova/api/openstack/placement/handlers/usage.py
@@ -13,6 +13,7 @@
 
 from oslo_serialization import jsonutils
 from oslo_utils import encodeutils
+from oslo_utils import timeutils
 import webob
 
 from nova.api.openstack.placement import microversion
@@ -64,6 +65,7 @@ def list_usages(req):
     """
     context = req.environ['placement.context']
     uuid = util.wsgi_path_item(req.environ, 'uuid')
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
 
     # Resource provider object needed for two things: If it is
     # NotFound we'll get a 404 here, which needs to happen because
@@ -85,6 +87,14 @@ def list_usages(req):
     response.body = encodeutils.to_utf8(jsonutils.dumps(
         _serialize_usages(resource_provider, usage)))
     req.response.content_type = 'application/json'
+    if want_version.matches((1, 15)):
+        req.response.cache_control = 'no-cache'
+        # While it would be possible to generate a last-modified time
+        # based on the collection of allocations that result in a usage
+        # value (with some spelunking in the SQL) that doesn't align with
+        # the question that is being asked in a request for usages: What
+        # is the usage, now? So the last-modified time is set to utcnow.
+        req.response.last_modified = timeutils.utcnow(with_timezone=True)
     return req.response
 
 
@@ -99,6 +109,7 @@ def get_total_usages(req):
     Return 404 Not Found if the wanted microversion does not match.
     """
     context = req.environ['placement.context']
+    want_version = req.environ[microversion.MICROVERSION_ENVIRON]
 
     schema = GET_USAGES_SCHEMA_1_9
 
@@ -115,4 +126,12 @@ def get_total_usages(req):
                    for resource in usages}}
     response.body = encodeutils.to_utf8(jsonutils.dumps(usages_dict))
     req.response.content_type = 'application/json'
+    if want_version.matches((1, 15)):
+        req.response.cache_control = 'no-cache'
+        # While it would be possible to generate a last-modified time
+        # based on the collection of allocations that result in a usage
+        # value (with some spelunking in the SQL) that doesn't align with
+        # the question that is being asked in a request for usages: What
+        # is the usage, now? So the last-modified time is set to utcnow.
+        req.response.last_modified = timeutils.utcnow(with_timezone=True)
     return req.response
diff --git a/nova/api/openstack/placement/microversion.py b/nova/api/openstack/placement/microversion.py
index d4a6a20cfbb4..030c7a61b8b3 100644
--- a/nova/api/openstack/placement/microversion.py
+++ b/nova/api/openstack/placement/microversion.py
@@ -54,9 +54,9 @@ VERSIONS = [
              # as GET. The 'allocation_requests' format in GET
              # /allocation_candidates is updated to be the same as well.
     '1.13',  # Adds POST /allocations to set allocations for multiple consumers
-             # as GET
     '1.14',  # Adds parent and root provider UUID on resource provider
              # representation and 'in_tree' filter on GET /resource_providers
+    '1.15',  # Include last-modified and cache-control headers
 ]
 
 
diff --git a/nova/api/openstack/placement/rest_api_version_history.rst b/nova/api/openstack/placement/rest_api_version_history.rst
index 5dc510a18193..380ad36541b5 100644
--- a/nova/api/openstack/placement/rest_api_version_history.rst
+++ b/nova/api/openstack/placement/rest_api_version_history.rst
@@ -197,3 +197,13 @@ A new ``in_tree=<UUID>`` parameter is now available in the ``GET
 /resource-providers`` API call. Supplying a UUID value for the ``in_tree``
 parameter will cause all resource providers within the "provider tree" of the
 provider matching ``<UUID>`` to be returned.
+
+1.15 Add 'last-modified' and 'cache-control' headers
+----------------------------------------------------
+
+Throughout the API, 'last-modified' headers have been added to GET responses
+and those PUT and POST responses that have bodies. The value is either the
+actual last modified time of the most recently modified associated database
+entity or the current time if there is no direct mapping to the database. In
+addition, 'cache-control: no-cache' headers are added where the 'last-modified'
+header has been added to prevent inadvertent caching of resources.
diff --git a/nova/api/openstack/placement/util.py b/nova/api/openstack/placement/util.py
index efb16dcbc71a..552ba2200607 100644
--- a/nova/api/openstack/placement/util.py
+++ b/nova/api/openstack/placement/util.py
@@ -17,6 +17,7 @@ import re
 import jsonschema
 from oslo_middleware import request_id
 from oslo_serialization import jsonutils
+from oslo_utils import timeutils
 from oslo_utils import uuidutils
 import webob
 
@@ -124,6 +125,25 @@ def json_error_formatter(body, status, title, environ):
     return {'errors': [error_dict]}
 
 
+def pick_last_modified(last_modified, obj):
+    """Choose max of last_modified and obj.updated_at or obj.created_at.
+
+    If updated_at is not implemented in `obj` use the current time in UTC.
+    """
+    try:
+        current_modified = (obj.updated_at or obj.created_at)
+    except NotImplementedError:
+        # If updated_at is not implemented, we are looking at objects that
+        # have not come from the database, so "now" is the right modified
+        # time.
+        current_modified = timeutils.utcnow(with_timezone=True)
+    if last_modified:
+        last_modified = max(last_modified, current_modified)
+    else:
+        last_modified = current_modified
+    return last_modified
+
+
 def require_content(content_type):
     """Decorator to require a content type in a handler."""
     def decorator(f):
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/aggregate.yaml b/nova/tests/functional/api/openstack/placement/gabbits/aggregate.yaml
index 377a3b62869f..c9c4de00b0dc 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/aggregate.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/aggregate.yaml
@@ -65,12 +65,19 @@ tests:
   status: 200
   response_headers:
       content-type: /application/json/
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
   response_json_paths:
       $.aggregates[0]: *agg_1
       $.aggregates[1]: *agg_2
 
 - name: get those aggregates
   GET: $LAST_URL
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
   response_json_paths:
       $.aggregates.`len`: 2
 
@@ -117,3 +124,26 @@ tests:
       - JSON does not validate
   response_json_paths:
       $.errors[0].title: Bad Request
+
+# The next two tests confirm that prior to version 1.15 we do
+# not set the cache-control or last-modified headers on either
+# PUT or GET.
+
+- name: put some aggregates v1.14
+  PUT: $LAST_URL
+  request_headers:
+      openstack-api-version: placement 1.14
+  data:
+      - *agg_1
+      - *agg_2
+  response_forbidden_headers:
+      - last-modified
+      - cache-control
+
+- name: get those aggregates v1.14
+  GET: $LAST_URL
+  request_headers:
+      openstack-api-version: placement 1.14
+  response_forbidden_headers:
+      - last-modified
+      - cache-control
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/allocation-candidates.yaml b/nova/tests/functional/api/openstack/placement/gabbits/allocation-candidates.yaml
index 52738b69ccb5..a32115e6883c 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/allocation-candidates.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/allocation-candidates.yaml
@@ -83,6 +83,11 @@ tests:
       # storage show correct capacity and usage
       $.provider_summaries["$ENVIRON['SS_UUID']"].resources[DISK_GB].capacity: 1900 # 1.0 * 2000 - 100G
       $.provider_summaries["$ENVIRON['SS_UUID']"].resources[DISK_GB].used: 0
+  response_forbidden_headers:
+      # In the default microversion in this file (1.10) the cache headers
+      # are not preset.
+      - cache-control
+      - last-modified
 
 # Verify the 1.12 format of the allocation_requests sub object which
 # changes from a list-list to dict-ish format.
@@ -111,3 +116,13 @@ tests:
       # Verify that shared storage provider only has DISK_GB listed in the
       # resource requests, but is listed twice
       $.allocation_requests..allocations["$ENVIRON['SS_UUID']"].resources[DISK_GB]: [100, 100]
+
+- name: get allocation candidates cache headers
+  GET: /allocation_candidates?resources=VCPU:1,MEMORY_MB:1024,DISK_GB:100
+  request_headers:
+      # microversion 1.15 to cause cache headers
+      openstack-api-version: placement 1.15
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/allocations.yaml b/nova/tests/functional/api/openstack/placement/gabbits/allocations.yaml
index b732d6be3045..ee3408eea360 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/allocations.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/allocations.yaml
@@ -373,6 +373,11 @@ tests:
                 DISK_GB: 2
                 VCPU: 8
   status: 204
+  # These headers should not be present in any microversion on PUT
+  # because there is no response body.
+  response_forbidden_headers:
+      - cache-control
+      - last-modified
 
 - name: get those allocations for consumer
   GET: /allocations/1835b1c9-1c61-45af-9eb3-3e0e9f29487b
@@ -409,3 +414,37 @@ tests:
       - Allocation for resource provider 'be8b9cba-e7db-4a12-a386-99b4242167fe' that does not exist
   response_json_paths:
       $.errors[0].title: Bad Request
+
+- name: get allocations for resource provider with cache headers 1.15
+  GET: /resource_providers/fcfa516a-abbe-45d1-8152-d5225d82e596/allocations
+  request_headers:
+      openstack-api-version: placement 1.15
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
+- name: get allocations for resource provider without cache headers 1.14
+  GET: /resource_providers/fcfa516a-abbe-45d1-8152-d5225d82e596/allocations
+  request_headers:
+      openstack-api-version: placement 1.14
+  response_forbidden_headers:
+      - cache-control
+      - last-modified
+
+- name: get allocations for consumer with cache headers 1.15
+  GET: /allocations/1835b1c9-1c61-45af-9eb3-3e0e9f29487b
+  request_headers:
+      openstack-api-version: placement 1.15
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
+- name: get allocations for consumer without cache headers 1.14
+  GET: /allocations/1835b1c9-1c61-45af-9eb3-3e0e9f29487b
+  request_headers:
+      openstack-api-version: placement 1.14
+  response_forbidden_headers:
+      - cache-control
+      - last-modified
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/basic-http.yaml b/nova/tests/functional/api/openstack/placement/gabbits/basic-http.yaml
index 1c0dd6fcc5f1..244369bfdc3d 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/basic-http.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/basic-http.yaml
@@ -159,3 +159,20 @@ tests:
       $.errors[0].title:  Not Found
   response_strings:
       - The resource could not be found.
+
+- name: root at 1.15 has cache headers
+  GET: /
+  request_headers:
+      openstack-api-version: placement 1.15
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
+- name: root at 1.14 no cache headers
+  GET: /
+  request_headers:
+      openstack-api-version: placement 1.14
+  response_forbidden_headers:
+      - last-modified
+      - cache-control
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/inventory.yaml b/nova/tests/functional/api/openstack/placement/gabbits/inventory.yaml
index 0e59eeddf85a..5ab3a8390113 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/inventory.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/inventory.yaml
@@ -166,6 +166,13 @@ tests:
 - name: get that inventory
   GET: $LOCATION
   status: 200
+  request_headers:
+      # set microversion to 1.15 to get timestamp headers
+      openstack-api-version: placement 1.15
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
   response_json_paths:
       $.resource_provider_generation: 1
       $.total: 2048
@@ -175,6 +182,15 @@ tests:
       $.step_size: 10
       $.allocation_ratio: 1.0
 
+- name: get inventory v1.14 no cache headers
+  GET: $LAST_URL
+  status: 200
+  request_headers:
+      openstack-api-version: placement 1.14
+  response_forbidden_headers:
+      - cache-control
+      - last-modified
+
 - name: modify the inventory
   PUT: $LAST_URL
   request_headers:
@@ -310,6 +326,13 @@ tests:
 
 - name: get list of inventories
   GET: /resource_providers/$ENVIRON['RP_UUID']/inventories
+  request_headers:
+      # set microversion to 1.15 to get timestamp headers
+      openstack-api-version: placement 1.15
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
   response_json_paths:
       $.resource_provider_generation: 2
       $.inventories.DISK_GB.total: 2048
@@ -407,6 +430,8 @@ tests:
   PUT: $LOCATION/inventories
   request_headers:
       content-type: application/json
+      # set microversion to 1.15 to get timestamp headers
+      openstack-api-version: placement 1.15
   data:
       resource_provider_generation: 0
       inventories:
@@ -415,6 +440,10 @@ tests:
         DISK_GB:
           total: 1024
   status: 200
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
   response_json_paths:
       $.resource_provider_generation: 1
       $.inventories.IPV4_ADDRESS.total: 253
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/microversion.yaml b/nova/tests/functional/api/openstack/placement/gabbits/microversion.yaml
index c2e8b6deb438..93110b615527 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/microversion.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/microversion.yaml
@@ -39,13 +39,13 @@ tests:
   response_json_paths:
       $.errors[0].title: Not Acceptable
 
-- name: latest microversion is 1.14
+- name: latest microversion is 1.15
   GET: /
   request_headers:
       openstack-api-version: placement latest
   response_headers:
       vary: /OpenStack-API-Version/
-      openstack-api-version: placement 1.14
+      openstack-api-version: placement 1.15
 
 - name: other accept header bad version
   GET: /
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/resource-classes-last-modified.yaml b/nova/tests/functional/api/openstack/placement/gabbits/resource-classes-last-modified.yaml
new file mode 100644
index 000000000000..e60244777770
--- /dev/null
+++ b/nova/tests/functional/api/openstack/placement/gabbits/resource-classes-last-modified.yaml
@@ -0,0 +1,117 @@
+# Confirm the behavior and presence of last-modified headers for resource
+# classes across multiple microversions.
+#
+# We have the following routes, with associated microversion, and bodies.
+#
+#    '/resource_classes': {
+#        'GET': resource_class.list_resource_classes,
+#         v1.2, body
+#        'POST': resource_class.create_resource_class
+#         v1.2, no body
+#    },
+#    '/resource_classes/{name}': {
+#        'GET': resource_class.get_resource_class,
+#         v1.2, body
+#        'PUT': resource_class.update_resource_class,
+#         v1.2, body, but time's arrow
+#         v1.7, no body
+#        'DELETE': resource_class.delete_resource_class,
+#         v1.2, no body
+#    },
+#
+# This means that in 1.15 we only expect last-modified headers for
+# the two GET requests, for the other requests we should confirm it
+# is not there.
+
+fixtures:
+    - APIFixture
+
+defaults:
+    request_headers:
+        x-auth-token: admin
+        accept: application/json
+        content-type: application/json
+        openstack-api-version: placement 1.15
+
+tests:
+
+- name: get resource classes
+  desc: last modified is now with standards only
+  GET: /resource_classes
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
+- name: create a custom class
+  PUT: /resource_classes/CUSTOM_MOO_MACHINE
+  status: 201
+  response_forbidden_headers:
+      - last-modified
+      - cache-control
+
+- name: get custom class
+  GET: $LAST_URL
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
+- name: get standard class
+  GET: /resource_classes/VCPU
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
+- name: post a resource class
+  POST: /resource_classes
+  data:
+      name: CUSTOM_ALPHA
+  status: 201
+  response_forbidden_headers:
+      - last-modified
+      - cache-control
+
+- name: get resource classes including custom
+  desc: last modified will still be now with customs because of standards
+  GET: /resource_classes
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
+- name: put a resource class 1.6 microversion
+  PUT: /resource_classes/CUSTOM_MOO_MACHINE
+  request_headers:
+      openstack-api-version: placement 1.6
+  data:
+      name: CUSTOM_BETA
+  status: 200
+  response_forbidden_headers:
+      - last-modified
+      - cache-control
+
+- name: get resource classes 1.14 microversion
+  GET: /resource_classes
+  request_headers:
+      openstack-api-version: placement 1.14
+  response_forbidden_headers:
+      - last-modified
+      - cache-control
+
+- name: get standard class 1.14 microversion
+  GET: /resource_classes/VCPU
+  request_headers:
+      openstack-api-version: placement 1.14
+  response_forbidden_headers:
+      - last-modified
+      - cache-control
+
+- name: get custom class 1.14 microversion
+  GET: $LAST_URL
+  request_headers:
+      openstack-api-version: placement 1.14
+  response_forbidden_headers:
+      - last-modified
+      - cache-control
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/resource-provider.yaml b/nova/tests/functional/api/openstack/placement/gabbits/resource-provider.yaml
index c0c7f53ce482..caf9c2f8763d 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/resource-provider.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/resource-provider.yaml
@@ -12,8 +12,15 @@ tests:
 
 - name: what is at resource providers
   GET: /resource_providers
+  request_headers:
+      # microversion 1.15 for cache headers
+      openstack-api-version: placement 1.15
   response_json_paths:
       $.resource_providers: []
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
 
 - name: non admin forbidden
   GET: /resource_providers
@@ -78,6 +85,12 @@ tests:
   GET: /resource_providers/$ENVIRON['RP_UUID']
   request_headers:
       content-type: application/json
+      openstack-api-version: placement 1.15
+  response_headers:
+      content-type: application/json
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
   response_json_paths:
       $.uuid: $ENVIRON['RP_UUID']
       $.name: $ENVIRON['RP_NAME']
@@ -104,6 +117,8 @@ tests:
 
 - name: list one resource providers
   GET: /resource_providers
+  request_headers:
+      openstack-api-version: placement 1.15
   response_json_paths:
       $.resource_providers.`len`: 1
       $.resource_providers[0].uuid: $ENVIRON['RP_UUID']
@@ -113,6 +128,10 @@ tests:
       $.resource_providers[0].links[?rel = "self"].href: /resource_providers/$ENVIRON['RP_UUID']
       $.resource_providers[0].links[?rel = "inventories"].href: /resource_providers/$ENVIRON['RP_UUID']/inventories
       $.resource_providers[0].links[?rel = "usages"].href: /resource_providers/$ENVIRON['RP_UUID']/usages
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
 
 - name: filter out all resource providers by name
   GET: /resource_providers?name=flubblebubble
@@ -181,11 +200,15 @@ tests:
   PUT: /resource_providers/$RESPONSE['$.resource_providers[0].uuid']
   request_headers:
       content-type: application/json
+      openstack-api-version: placement 1.15
   data:
       name: new name
   status: 200
   response_headers:
       content-type: /application/json/
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
   response_forbidden_headers:
       - location
   response_json_paths:
@@ -491,3 +514,11 @@ tests:
       - "Failed validating 'maxLength'"
   response_json_paths:
       $.errors[0].title: Bad Request
+
+- name: confirm no cache-control headers before 1.15
+  GET: /resource_providers
+  request_headers:
+      openstack-api-version: placement 1.14
+  response_forbidden_headers:
+      - cache-control
+      - last-modified
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/traits.yaml b/nova/tests/functional/api/openstack/placement/gabbits/traits.yaml
index 6300db6d3d19..0d5f911707a9 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/traits.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/traits.yaml
@@ -5,7 +5,8 @@ fixtures:
 defaults:
     request_headers:
         x-auth-token: admin
-        openstack-api-version: placement latest
+        # traits introduced in 1.6
+        openstack-api-version: placement 1.6
 
 tests:
 
@@ -34,6 +35,9 @@ tests:
     location: //traits/CUSTOM_TRAIT_1/
   response_forbidden_headers:
     - content-type
+    # PUT in 1.6 version should not have cache headers
+    - cache-control
+    - last-modified
 
 - name: create a trait which existed
   PUT: /traits/CUSTOM_TRAIT_1
@@ -48,6 +52,9 @@ tests:
   status: 204
   response_forbidden_headers:
       - content-type
+      # In early versions cache headers should not be present
+      - cache-control
+      - last-modified
 
 - name: get a non-existed trait
   GET: /traits/NON_EXISTED
@@ -56,6 +63,11 @@ tests:
 - name: delete a trait
   DELETE: /traits/CUSTOM_TRAIT_1
   status: 204
+  response_forbidden_headers:
+    - content-type
+    # DELETE in any version should not have cache headers
+    - cache-control
+    - last-modified
 
 - name: delete a non-existed trait
   DELETE: /traits/CUSTOM_NON_EXSITED
@@ -133,6 +145,61 @@ tests:
   response_strings:
     - "Invalid query string parameters: Additional properties are not allowed"
 
+- name: list traits 1.14 no cache headers
+  GET: /traits
+  request_headers:
+      openstack-api-version: placement 1.14
+  response_forbidden_headers:
+    - cache-control
+    - last-modified
+
+- name: list traits 1.15 has cache headers
+  GET: /traits
+  request_headers:
+      openstack-api-version: placement 1.15
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
+- name: get trait 1.14 no cache headers
+  GET: /traits/CUSTOM_TRAIT_1
+  request_headers:
+      openstack-api-version: placement 1.14
+  status: 204
+  response_forbidden_headers:
+    - cache-control
+    - last-modified
+
+- name: get trait 1.15 has cache headers
+  GET: /traits/CUSTOM_TRAIT_1
+  request_headers:
+      openstack-api-version: placement 1.15
+  status: 204
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
+- name: put trait 1.14 no cache headers
+  PUT: /traits/CUSTOM_TRAIT_1
+  request_headers:
+      openstack-api-version: placement 1.14
+  status: 204
+  response_forbidden_headers:
+    - cache-control
+    - last-modified
+
+- name: put trait 1.15 has cache headers
+  PUT: /traits/CUSTOM_TRAIT_1
+  request_headers:
+      openstack-api-version: placement 1.15
+  status: 204
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
 - name: post new resource provider
   POST: /resource_providers
   request_headers:
@@ -152,6 +219,10 @@ tests:
   response_json_paths:
     $.resource_provider_generation: 0
     $.traits.`len`: 0
+  response_forbidden_headers:
+    # In 1.6 no cache headers
+    - cache-control
+    - last-modified
 
 - name: set traits for resource provider
   PUT: /resource_providers/$ENVIRON['RP_UUID']/traits
@@ -169,6 +240,10 @@ tests:
   response_strings:
     - CUSTOM_TRAIT_1
     - CUSTOM_TRAIT_2
+  response_forbidden_headers:
+    # In 1.6 no cache headers
+    - cache-control
+    - last-modified
 
 - name: get associated traits
   GET: /traits?associated=true
@@ -272,3 +347,58 @@ tests:
   status: 404
   response_strings:
     - No resource provider with uuid non_existed found
+
+- name: empty traits for resource provider 1.15 has cache headers
+  GET: /resource_providers/$ENVIRON['RP_UUID']/traits
+  request_headers:
+    openstack-api-version: placement 1.15
+  response_headers:
+    cache-control: no-cache
+    # Does last-modified look like a legit timestamp?
+    last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
+- name: update rp trait 1.14 no cache headers
+  PUT: /resource_providers/$ENVIRON['RP_UUID']/traits
+  data:
+    traits:
+        - CUSTOM_TRAIT_1
+        - CUSTOM_TRAIT_2
+    resource_provider_generation: 2
+  request_headers:
+    openstack-api-version: placement 1.14
+    content-type: application/json
+  response_forbidden_headers:
+    - cache-control
+    - last-modified
+
+- name: update rp trait 1.15 has cache headers
+  PUT: /resource_providers/$ENVIRON['RP_UUID']/traits
+  data:
+    traits:
+        - CUSTOM_TRAIT_1
+        - CUSTOM_TRAIT_2
+    resource_provider_generation: 3
+  request_headers:
+    openstack-api-version: placement 1.15
+    content-type: application/json
+  response_headers:
+    cache-control: no-cache
+    # Does last-modified look like a legit timestamp?
+    last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
+- name: list traits for resource provider 1.14 no cache headers
+  GET: /resource_providers/$ENVIRON['RP_UUID']/traits
+  request_headers:
+    openstack-api-version: placement 1.14
+  response_forbidden_headers:
+    - cache-control
+    - last-modified
+
+- name: list traits for resource provider 1.15 has cache headers
+  GET: /resource_providers/$ENVIRON['RP_UUID']/traits
+  request_headers:
+    openstack-api-version: placement 1.15
+  response_headers:
+    cache-control: no-cache
+    # Does last-modified look like a legit timestamp?
+    last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/usage.yaml b/nova/tests/functional/api/openstack/placement/gabbits/usage.yaml
index b34c0255727e..8fa8995652d9 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/usage.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/usage.yaml
@@ -38,6 +38,21 @@ tests:
   response_json_paths:
       usages: {}
 
+- name: get usages no cache headers base microversion
+  GET: $LAST_URL
+  response_forbidden_headers:
+      - last-modified
+      - cache-control
+
+- name: get usages cache headers 1.15
+  GET: $LAST_URL
+  request_headers:
+      openstack-api-version: placement 1.15
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
+
 - name: get total usages earlier version
   GET: /usages?project_id=$ENVIRON['PROJECT_ID']
   request_headers:
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/with-allocations.yaml b/nova/tests/functional/api/openstack/placement/gabbits/with-allocations.yaml
index eaa498ebe765..d19fb453e033 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/with-allocations.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/with-allocations.yaml
@@ -65,6 +65,10 @@ tests:
   request_headers:
       openstack-api-version: placement 1.9
   status: 200
+  # In pre 1.15 microversions cache headers not present
+  response_forbidden_headers:
+      - last-modified
+      - cache-control
   response_json_paths:
       $.usages.DISK_GB: 20
       $.usages.VCPU: 1
@@ -87,3 +91,12 @@ tests:
       $.project_id: $ENVIRON['PROJECT_ID']
       $.user_id: $ENVIRON['USER_ID']
       $.`len`: 3
+
+- name: get total usages with cache headers
+  GET: /usages?project_id=$ENVIRON['PROJECT_ID']&user_id=$ENVIRON['ALT_USER_ID']
+  request_headers:
+      openstack-api-version: placement 1.15
+  response_headers:
+      cache-control: no-cache
+      # Does last-modified look like a legit timestamp?
+      last-modified:  /^\w+, \d+ \w+ \d{4} [\d:]+ GMT$/
diff --git a/nova/tests/unit/api/openstack/placement/test_handler.py b/nova/tests/unit/api/openstack/placement/test_handler.py
index 3e75ccc77287..a83f89149ded 100644
--- a/nova/tests/unit/api/openstack/placement/test_handler.py
+++ b/nova/tests/unit/api/openstack/placement/test_handler.py
@@ -19,6 +19,7 @@ import webob
 
 from nova.api.openstack.placement import handler
 from nova.api.openstack.placement.handlers import root
+from nova.api.openstack.placement import microversion
 from nova import test
 from nova.tests import uuidsentinel
 
@@ -35,6 +36,9 @@ def _environ(path='/moo', method='GET'):
         'SERVER_NAME': 'example.com',
         'SERVER_PORT': '80',
         'wsgi.url_scheme': 'http',
+        # The microversion version value is not used, but it
+        # needs to be set to avoid a KeyError.
+        microversion.MICROVERSION_ENVIRON: microversion.Version(1, 12),
     }
 
 
diff --git a/nova/tests/unit/api/openstack/placement/test_util.py b/nova/tests/unit/api/openstack/placement/test_util.py
index aede250a7237..c7b7cb4e5948 100644
--- a/nova/tests/unit/api/openstack/placement/test_util.py
+++ b/nova/tests/unit/api/openstack/placement/test_util.py
@@ -13,8 +13,12 @@
 """Unit tests for the utility functions used by the placement API."""
 
 
+import datetime
+
 import fixtures
+import mock
 from oslo_middleware import request_id
+from oslo_utils import timeutils
 import webob
 
 import six.moves.urllib.parse as urlparse
@@ -594,3 +598,83 @@ class TestParseQsResourcesAndTraits(test.NoDBTestCase):
               '&required2=CUSTOM_SWITCH_BIG,CUSTOM_PHYSNET_PROD'
               '&resources3=CUSTOM_MAGIC:123')
         self.assertRaises(webob.exc.HTTPBadRequest, self.do_parse, qs)
+
+
+class TestPickLastModified(test.NoDBTestCase):
+
+    def setUp(self):
+        super(TestPickLastModified, self).setUp()
+        self.resource_provider = rp_obj.ResourceProvider(
+            name=uuidsentinel.rp_name, uuid=uuidsentinel.rp_uuid)
+
+    def test_updated_versus_none(self):
+        now = timeutils.utcnow(with_timezone=True)
+        self.resource_provider.updated_at = now
+        self.resource_provider.created_at = now
+        chosen_time = util.pick_last_modified(None, self.resource_provider)
+        self.assertEqual(now, chosen_time)
+
+    def test_created_versus_none(self):
+        now = timeutils.utcnow(with_timezone=True)
+        self.resource_provider.created_at = now
+        self.resource_provider.updated_at = None
+        chosen_time = util.pick_last_modified(None, self.resource_provider)
+        self.assertEqual(now, chosen_time)
+
+    def test_last_modified_less(self):
+        now = timeutils.utcnow(with_timezone=True)
+        less = now - datetime.timedelta(seconds=300)
+        self.resource_provider.updated_at = now
+        self.resource_provider.created_at = now
+        chosen_time = util.pick_last_modified(less, self.resource_provider)
+        self.assertEqual(now, chosen_time)
+
+    def test_last_modified_more(self):
+        now = timeutils.utcnow(with_timezone=True)
+        more = now + datetime.timedelta(seconds=300)
+        self.resource_provider.updated_at = now
+        self.resource_provider.created_at = now
+        chosen_time = util.pick_last_modified(more, self.resource_provider)
+        self.assertEqual(more, chosen_time)
+
+    def test_last_modified_same(self):
+        now = timeutils.utcnow(with_timezone=True)
+        self.resource_provider.updated_at = now
+        self.resource_provider.created_at = now
+        chosen_time = util.pick_last_modified(now, self.resource_provider)
+        self.assertEqual(now, chosen_time)
+
+    def test_no_object_time_fields_less(self):
+        # An unsaved ovo will not have the created_at or updated_at fields
+        # present on the object at all.
+        now = timeutils.utcnow(with_timezone=True)
+        less = now - datetime.timedelta(seconds=300)
+        with mock.patch('oslo_utils.timeutils.utcnow') as mock_utc:
+            mock_utc.return_value = now
+            chosen_time = util.pick_last_modified(
+                less, self.resource_provider)
+            self.assertEqual(now, chosen_time)
+            mock_utc.assert_called_once_with(with_timezone=True)
+
+    def test_no_object_time_fields_more(self):
+        # An unsaved ovo will not have the created_at or updated_at fields
+        # present on the object at all.
+        now = timeutils.utcnow(with_timezone=True)
+        more = now + datetime.timedelta(seconds=300)
+        with mock.patch('oslo_utils.timeutils.utcnow') as mock_utc:
+            mock_utc.return_value = now
+            chosen_time = util.pick_last_modified(
+                more, self.resource_provider)
+            self.assertEqual(more, chosen_time)
+            mock_utc.assert_called_once_with(with_timezone=True)
+
+    def test_no_object_time_fields_none(self):
+        # An unsaved ovo will not have the created_at or updated_at fields
+        # present on the object at all.
+        now = timeutils.utcnow(with_timezone=True)
+        with mock.patch('oslo_utils.timeutils.utcnow') as mock_utc:
+            mock_utc.return_value = now
+            chosen_time = util.pick_last_modified(
+                None, self.resource_provider)
+            self.assertEqual(now, chosen_time)
+            mock_utc.assert_called_once_with(with_timezone=True)
diff --git a/releasenotes/notes/placement-last-modified-cf43aece4c54fc97.yaml b/releasenotes/notes/placement-last-modified-cf43aece4c54fc97.yaml
new file mode 100644
index 000000000000..f97780a56498
--- /dev/null
+++ b/releasenotes/notes/placement-last-modified-cf43aece4c54fc97.yaml
@@ -0,0 +1,10 @@
+---
+features:
+  - |
+    Throughout the API, in microversion 1.15, 'last-modified' headers have been
+    added to GET responses and those PUT and POST responses that have bodies.
+    The value is either the actual last modified time of the most recently
+    modified associated database entity or the current time if there is no
+    direct mapping to the database. In addition, 'cache-control: no-cache'
+    headers are added where the 'last-modified' header has been added to
+    prevent inadvertent caching of resources.