Capture instance metadata in reserved namespace.

The concept of a reserved namespace for instance metadata
is intended to support the Heat autoscaling use-case.

When spinning up new instances in a autoscaling group, Heat
will set some additional user metadata on the instances to
identify their group membership.

Previously, instance user metadata was not captured in the
metering store and thus could not be queried on.

Now the reserved namespace(s) are used to signal to the
compute agent that some user metadata should not be discarded.
This allows the statistics for a group of associated instances
to be aggregated in a single query.

Change-Id: I838db38bf2e01a0e5e4d76f3f401d7f41e1dff57

ceilometer/compute/instance.py

@@ -17,6 +17,19 @@
 # under the License.
 """Common code for working with instances
 """
+from oslo.config import cfg
+
+OPTS = [
+    cfg.ListOpt('reserved_metadata_namespace',
+                default=['metering.'],
+                help='list of metadata prefixes resevred for metering use',
+                ),
+    cfg.IntOpt('reserved_metadata_length',
+               default=256,
+               help='limit on length of reserved metadata values'),
+]
+
+cfg.CONF.register_opts(OPTS)
 
 INSTANCE_PROPERTIES = [
     # Identity properties
@@ -36,6 +49,24 @@ INSTANCE_PROPERTIES = [
     'vcpus']
 
 
+def add_reserved_user_metadata(instance, metadata):
+    limit = cfg.CONF.reserved_metadata_length
+    user_metadata = {}
+    for prefix in cfg.CONF.reserved_metadata_namespace:
+        md = dict(
+            (k[len(prefix):].replace('.', '_'),
+             v[:limit] if isinstance(v, basestring) else v)
+            for k, v in instance.metadata.items()
+            if (k.startswith(prefix) and
+                k[len(prefix):].replace('.', '_') not in metadata)
+        )
+        user_metadata.update(md)
+    if user_metadata:
+        metadata['user_metadata'] = user_metadata
+
+    return metadata
+
+
 def get_metadata_from_object(instance):
     """Return a metadata dictionary for the instance.
     """
@@ -57,4 +88,5 @@ def get_metadata_from_object(instance):
 
     for name in INSTANCE_PROPERTIES:
         metadata[name] = getattr(instance, name, u'')
-    return metadata
+
+    return add_reserved_user_metadata(instance, metadata)

tests/compute/test_instance.py

@@ -67,7 +67,10 @@ class TestLocationMetadata(base.TestCase):
                                               'links': [{"rel": "bookmark",
                                                          'href': 2}]},
                                     'flavor': {'id': 1},
-                                    'hostId': '1234-5678'}
+                                    'hostId': '1234-5678',
+                                    'metadata': {'metering.autoscale.group':
+                                                 'X' * 512,
+                                                 'metering.ephemeral_gb': 42}}
 
         self.instance = FauxInstance(**self.INSTANCE_PROPERTIES)
         self.instance.host = 'made-up-hostname'
@@ -93,6 +96,10 @@ class TestLocationMetadata(base.TestCase):
                 assert actual == iprops['image']['id']
             elif name == 'image_ref_url':
                 assert actual == iprops['image']['links'][0]['href']
+            elif name == 'user_metadata':
+                expected = iprops['metadata']['metering.autoscale.group'][:256]
+                self.assertEqual(actual['autoscale_group'], expected)
+                self.assertEqual(len(actual), 1)
             else:
                 assert actual == iprops[name]