This patch adds support for working with instances by UUID in addition to integer IDs.

The Zone Scheduler routing mechanics were changed slightly so that when an UUID is passed in, it checks to see whether the item is available locally.

If it isn't it re-routes to a child zone. 

If it is available locally, it substitutes the UUID with the integer ID and calls the wrapped function. This is the 'trick' allows us to not change any of the virt-layer code-- everything still uses integer IDs locally.

nova/scheduler/api.py

@@ -24,6 +24,7 @@ from nova import exception
 from nova import flags
 from nova import log as logging
 from nova import rpc
+from nova import utils
 
 from eventlet import greenpool
 
@@ -201,38 +202,78 @@ class RedirectResult(exception.Error):
 
 
 class reroute_compute(object):
-    """Decorator used to indicate that the method should
-       delegate the call the child zones if the db query
-       can't find anything."""
+    """
+    reroute_compute is responsible for trying to lookup a resource in the
+    current zone and if it's not found there, delegating the call to the
+    child zones.
+
+    Since reroute_compute will be making 'cross-zone' calls, the ID for the
+    object must come in as a UUID-- if we receive an integer ID, we bail.
+
+    The steps involved are:
+
+        1. Validate that item_id is UUID like
+
+        2. Lookup item by UUID in the zone local database
+
+        3. If the item was found, then extract integer ID, and pass that to
+           the wrapped method. (This ensures that zone-local code can
+           continue to use integer IDs).
+
+        4. If the item was not found, we delgate the call to a child zone
+           using the UUID.
+    """
     def __init__(self, method_name):
         self.method_name = method_name
 
+    def _route_to_child_zones(self, context, collection, item_uuid):
+        if not FLAGS.enable_zone_routing:
+            raise exception.InstanceNotFound(instance_id=item_uuid)
+
+        zones = db.zone_get_all(context)
+        if not zones:
+            raise exception.InstanceNotFound(instance_id=item_uuid)
+
+        # Ask the children to provide an answer ...
+        LOG.debug(_("Asking child zones ..."))
+        result = self._call_child_zones(zones,
+                    wrap_novaclient_function(_issue_novaclient_command,
+                           collection, self.method_name, item_uuid))
+        # Scrub the results and raise another exception
+        # so the API layers can bail out gracefully ...
+        raise RedirectResult(self.unmarshall_result(result))
+
     def __call__(self, f):
         def wrapped_f(*args, **kwargs):
-            collection, context, item_id = \
+            collection, context, item_id_or_uuid = \
                             self.get_collection_context_and_id(args, kwargs)
-            try:
-                # Call the original function ...
+
+            attempt_reroute = False
+            if utils.is_uuid_like(item_id_or_uuid):
+                item_uuid = item_id_or_uuid
+                try:
+                    instance = db.instance_get_by_uuid(context, item_uuid)
+                except exception.InstanceNotFound, e:
+                    # NOTE(sirp): since a UUID was passed in, we can attempt
+                    # to reroute to a child zone
+                    attempt_reroute = True
+                    LOG.debug(_("Instance %(item_uuid)s not found "
+                                        "locally: '%(e)s'" % locals()))
+                else:
+                    # NOTE(sirp): since we're not re-routing in this case, and
+                    # we we were passed a UUID, we need to replace that UUID
+                    # with an integer ID in the argument list so that the
+                    # zone-local code can continue to use integer IDs.
+                    item_id = instance['id']
+                    args = list(args)      # needs to be mutable to replace
+                    self.replace_uuid_with_id(args, kwargs, item_id)
+
+            if attempt_reroute:
+                return self._route_to_child_zones(context, collection,
+                        item_uuid)
+            else:
                 return f(*args, **kwargs)
-            except exception.InstanceNotFound, e:
-                LOG.debug(_("Instance %(item_id)s not found "
-                                    "locally: '%(e)s'" % locals()))
 
-                if not FLAGS.enable_zone_routing:
-                    raise
-
-                zones = db.zone_get_all(context)
-                if not zones:
-                    raise
-
-                # Ask the children to provide an answer ...
-                LOG.debug(_("Asking child zones ..."))
-                result = self._call_child_zones(zones,
-                            wrap_novaclient_function(_issue_novaclient_command,
-                                   collection, self.method_name, item_id))
-                # Scrub the results and raise another exception
-                # so the API layers can bail out gracefully ...
-                raise RedirectResult(self.unmarshall_result(result))
         return wrapped_f
 
     def _call_child_zones(self, zones, function):
@@ -251,6 +292,18 @@ class reroute_compute(object):
             instance_id = args[2]
         return ("servers", context, instance_id)
 
+    @staticmethod
+    def replace_uuid_with_id(args, kwargs, replacement_id):
+        """
+        Extracts the UUID parameter from the arg or kwarg list and replaces
+        it with an integer ID.
+        """
+        if 'instance_id' in kwargs:
+            kwargs['instance_id'] = replacement_id
+        elif len(args) > 1:
+            args.pop(2)
+            args.insert(2, replacement_id)
+
     def unmarshall_result(self, zone_responses):
         """Result is a list of responses from each child zone.
         Each decorator derivation is responsible to turning this