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.

13 files changed, 313 insertions, 73 deletions

diff --git a/nova/api/openstack/ips.py b/nova/api/openstack/ips.py
index abea71830..71646b6d3 100644
--- a/nova/api/openstack/ips.py
+++ b/nova/api/openstack/ips.py
@@ -32,25 +32,24 @@ class Controller(object):
         self.compute_api = nova.compute.API()
         self.builder = nova.api.openstack.views.addresses.ViewBuilderV10()
 
-    def index(self, req, server_id):
+    def _get_instance(self, req, server_id):
         try:
-            instance = self.compute_api.get(req.environ['nova.context'], id)
+            instance = self.compute_api.get(
+                req.environ['nova.context'], server_id)
         except nova.exception.NotFound:
             return faults.Fault(exc.HTTPNotFound())
+        return instance
+
+    def index(self, req, server_id):
+        instance = self._get_instance(req, server_id)
         return {'addresses': self.builder.build(instance)}
 
     def public(self, req, server_id):
-        try:
-            instance = self.compute_api.get(req.environ['nova.context'], id)
-        except nova.exception.NotFound:
-            return faults.Fault(exc.HTTPNotFound())
+        instance = self._get_instance(req, server_id)
         return {'public': self.builder.build_public_parts(instance)}
 
     def private(self, req, server_id):
-        try:
-            instance = self.compute_api.get(req.environ['nova.context'], id)
-        except nova.exception.NotFound:
-            return faults.Fault(exc.HTTPNotFound())
+        instance = self._get_instance(req, server_id)
         return {'private': self.builder.build_private_parts(instance)}
 
     def show(self, req, server_id, id):
diff --git a/nova/api/openstack/views/servers.py b/nova/api/openstack/views/servers.py
index 245d0e3fa..cbfa5aae7 100644
--- a/nova/api/openstack/views/servers.py
+++ b/nova/api/openstack/views/servers.py
@@ -75,7 +75,7 @@ class ViewBuilder(object):
         }
 
         inst_dict = {
-            'id': int(inst['id']),
+            'id': inst['id'],
             'name': inst['display_name'],
             'addresses': self.addresses_builder.build(inst),
             'status': power_mapping[inst.get('state')]}
@@ -99,6 +99,7 @@ class ViewBuilder(object):
         self._build_image(inst_dict, inst)
         self._build_flavor(inst_dict, inst)
 
+        inst_dict['uuid'] = inst['uuid']
         return dict(server=inst_dict)
 
     def _build_image(self, response, inst):
diff --git a/nova/compute/api.py b/nova/compute/api.py
index b81aecb70..e6cffb6b3 100644
--- a/nova/compute/api.py
+++ b/nova/compute/api.py
@@ -579,8 +579,15 @@ class API(base.Base):
 
     def get(self, context, instance_id):
         """Get a single instance with the given instance_id."""
-        rv = self.db.instance_get(context, instance_id)
-        return dict(rv.iteritems())
+        # NOTE(sirp): id used to be exclusively integer IDs; now we're
+        # accepting both UUIDs and integer IDs. The handling of this
+        # is done in db/sqlalchemy/api/instance_get
+        if utils.is_uuid_like(instance_id):
+            uuid = instance_id
+            instance = self.db.instance_get_by_uuid(context, uuid)
+        else:
+            instance = self.db.instance_get(context, instance_id)
+        return dict(instance.iteritems())
 
     @scheduler_api.reroute_compute("get")
     def routing_get(self, context, instance_id):
diff --git a/nova/compute/manager.py b/nova/compute/manager.py
index 8ab744855..a7ec021b8 100644
--- a/nova/compute/manager.py
+++ b/nova/compute/manager.py
@@ -783,7 +783,6 @@ class ComputeManager(manager.SchedulerDependentManager):
     def get_diagnostics(self, context, instance_id):
         """Retrieve diagnostics for an instance on this host."""
         instance_ref = self.db.instance_get(context, instance_id)
-
         if instance_ref["state"] == power_state.RUNNING:
             LOG.audit(_("instance %s: retrieving diagnostics"), instance_id,
                       context=context)
diff --git a/nova/db/api.py b/nova/db/api.py
index 117c235ea..5fd081ca8 100644
--- a/nova/db/api.py
+++ b/nova/db/api.py
@@ -419,6 +419,11 @@ def instance_stop(context, instance_id):
     return IMPL.instance_stop(context, instance_id)
 
 
+def instance_get_by_uuid(context, uuid):
+    """Get an instance or raise if it does not exist."""
+    return IMPL.instance_get_by_uuid(context, uuid)
+
+
 def instance_get(context, instance_id):
     """Get an instance or raise if it does not exist."""
     return IMPL.instance_get(context, instance_id)
diff --git a/nova/db/sqlalchemy/api.py b/nova/db/sqlalchemy/api.py
index 81569e98c..a7e5125d5 100644
--- a/nova/db/sqlalchemy/api.py
+++ b/nova/db/sqlalchemy/api.py
@@ -797,6 +797,8 @@ def instance_create(context, values):
     values['metadata'] = _metadata_refs(values.get('metadata'))
 
     instance_ref = models.Instance()
+    instance_ref['uuid'] = str(utils.gen_uuid())
+
     instance_ref.update(values)
 
     session = get_session()
@@ -859,37 +861,46 @@ def instance_stop(context, instance_id):
 
 
 @require_context
+def instance_get_by_uuid(context, uuid, session=None):
+    partial = _build_instance_get(context, session=session)
+    result = partial.filter_by(uuid=uuid)
+    result = result.first()
+    if not result:
+        # FIXME(sirp): it would be nice if InstanceNotFound would accept a
+        # uuid parameter as well
+        raise exception.InstanceNotFound(instance_id=uuid)
+    return result
+
+
+@require_context
 def instance_get(context, instance_id, session=None):
+    partial = _build_instance_get(context, session=session)
+    result = partial.filter_by(id=instance_id)
+    result = result.first()
+    if not result:
+        raise exception.InstanceNotFound(instance_id=instance_id)
+    return result
+
+
+@require_context
+def _build_instance_get(context, session=None):
     if not session:
         session = get_session()
-    result = None
+
+    partial = session.query(models.Instance).\
+                     options(joinedload_all('fixed_ip.floating_ips')).\
+                     options(joinedload_all('security_groups.rules')).\
+                     options(joinedload('volumes')).\
+                     options(joinedload_all('fixed_ip.network')).\
+                     options(joinedload('metadata')).\
+                     options(joinedload('instance_type'))
 
     if is_admin_context(context):
-        result = session.query(models.Instance).\
-                         options(joinedload_all('fixed_ip.floating_ips')).\
-                         options(joinedload_all('security_groups.rules')).\
-                         options(joinedload('volumes')).\
-                         options(joinedload_all('fixed_ip.network')).\
-                         options(joinedload('metadata')).\
-                         options(joinedload('instance_type')).\
-                         filter_by(id=instance_id).\
-                         filter_by(deleted=can_read_deleted(context)).\
-                         first()
+        partial = partial.filter_by(deleted=can_read_deleted(context))
     elif is_user_context(context):
-        result = session.query(models.Instance).\
-                         options(joinedload_all('fixed_ip.floating_ips')).\
-                         options(joinedload_all('security_groups.rules')).\
-                         options(joinedload('volumes')).\
-                         options(joinedload('metadata')).\
-                         options(joinedload('instance_type')).\
-                         filter_by(project_id=context.project_id).\
-                         filter_by(id=instance_id).\
-                         filter_by(deleted=False).\
-                         first()
-    if not result:
-        raise exception.InstanceNotFound(instance_id=instance_id)
-
-    return result
+        partial = partial.filter_by(project_id=context.project_id).\
+                        filter_by(deleted=False)
+    return partial
 
 
 @require_admin_context
diff --git a/nova/db/sqlalchemy/migrate_repo/versions/025_add_uuid_to_instances.py b/nova/db/sqlalchemy/migrate_repo/versions/025_add_uuid_to_instances.py
new file mode 100644
index 000000000..27f30d536
--- /dev/null
+++ b/nova/db/sqlalchemy/migrate_repo/versions/025_add_uuid_to_instances.py
@@ -0,0 +1,43 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright 2011 OpenStack LLC.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from sqlalchemy import Column, Integer, MetaData, String, Table
+
+from nova import utils
+
+
+meta = MetaData()
+
+instances = Table("instances", meta,
+        Column("id", Integer(), primary_key=True, nullable=False))
+uuid_column = Column("uuid", String(36))
+
+
+def upgrade(migrate_engine):
+    meta.bind = migrate_engine
+    instances.create_column(uuid_column)
+
+    rows = migrate_engine.execute(instances.select())
+    for row in rows:
+        instance_uuid = str(utils.gen_uuid())
+        migrate_engine.execute(instances.update()\
+                .where(instances.c.id == row[0])\
+                .values(uuid=instance_uuid))
+
+
+def downgrade(migrate_engine):
+    meta.bind = migrate_engine
+    instances.drop_column(uuid_column)
diff --git a/nova/db/sqlalchemy/models.py b/nova/db/sqlalchemy/models.py
index 23e1bd112..81711545a 100644
--- a/nova/db/sqlalchemy/models.py
+++ b/nova/db/sqlalchemy/models.py
@@ -233,6 +233,7 @@ class Instance(BASE, NovaBase):
 
     os_type = Column(String(255))
     vm_mode = Column(String(255))
+    uuid = Column(String(36))
 
     # TODO(vish): see Ewan's email about state improvements, probably
     #             should be in a driver base class or some such
diff --git a/nova/scheduler/api.py b/nova/scheduler/api.py
index 3b3195c2e..1bb047e2e 100644
--- a/nova/scheduler/api.py
+++ b/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
diff --git a/nova/tests/api/openstack/test_servers.py b/nova/tests/api/openstack/test_servers.py
index 8357df594..05de6e2a9 100644
--- a/nova/tests/api/openstack/test_servers.py
+++ b/nova/tests/api/openstack/test_servers.py
@@ -49,10 +49,22 @@ FLAGS = flags.FLAGS
 FLAGS.verbose = True
 
 
-def return_server(context, id):
+FAKE_UUID = 'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa'
+
+
+def fake_gen_uuid():
+    return FAKE_UUID
+
+
+def return_server_by_id(context, id):
     return stub_instance(id)
 
 
+def return_server_by_uuid(context, uuid):
+    id = 1
+    return stub_instance(id, uuid=uuid)
+
+
 def return_server_with_addresses(private, public):
     def _return_server(context, id):
         return stub_instance(id, private_address=private,
@@ -111,7 +123,8 @@ def instance_address(context, instance_id):
 
 
 def stub_instance(id, user_id=1, private_address=None, public_addresses=None,
-                  host=None, power_state=0, reservation_id=""):
+                  host=None, power_state=0, reservation_id="",
+                  uuid=FAKE_UUID):
     metadata = []
     metadata.append(InstanceMetadata(key='seq', value=id))
 
@@ -129,7 +142,7 @@ def stub_instance(id, user_id=1, private_address=None, public_addresses=None,
         server_name = "reservation_%s" % (reservation_id, )
 
     instance = {
-        "id": id,
+        "id": int(id),
         "admin_pass": "",
         "user_id": user_id,
         "project_id": "",
@@ -157,7 +170,8 @@ def stub_instance(id, user_id=1, private_address=None, public_addresses=None,
         "display_name": server_name,
         "display_description": "",
         "locked": False,
-        "metadata": metadata}
+        "metadata": metadata,
+        "uuid": uuid}
 
     instance["fixed_ip"] = {
         "address": private_address,
@@ -196,8 +210,11 @@ class ServersTest(test.TestCase):
         fakes.stub_out_auth(self.stubs)
         fakes.stub_out_key_pair_funcs(self.stubs)
         fakes.stub_out_image_service(self.stubs)
+        self.stubs.Set(utils, 'gen_uuid', fake_gen_uuid)
         self.stubs.Set(nova.db.api, 'instance_get_all', return_servers)
-        self.stubs.Set(nova.db.api, 'instance_get', return_server)
+        self.stubs.Set(nova.db.api, 'instance_get', return_server_by_id)
+        self.stubs.Set(nova.db, 'instance_get_by_uuid',
+                       return_server_by_uuid)
         self.stubs.Set(nova.db.api, 'instance_get_all_by_user',
                        return_servers)
         self.stubs.Set(nova.db.api, 'instance_add_security_group',
@@ -229,6 +246,36 @@ class ServersTest(test.TestCase):
         self.assertEqual(res_dict['server']['id'], 1)
         self.assertEqual(res_dict['server']['name'], 'server1')
 
+    def test_get_server_by_uuid(self):
+        """
+        The steps involved with resolving a UUID are pretty complicated;
+        here's what's happening in this scenario:
+
+        1. Show is calling `routing_get`
+
+        2. `routing_get` is wrapped by `reroute_compute` which does the work
+           of resolving requests to child zones.
+
+        3. `reroute_compute` looks up the UUID by hitting the stub
+           (returns_server_by_uuid)
+
+        4. Since the stub return that the record exists, `reroute_compute`
+           considers the request to be 'zone local', so it replaces the UUID
+           in the argument list with an integer ID and then calls the inner
+           function ('get').
+
+        5. The call to `get` hits the other stub 'returns_server_by_id` which
+           has the UUID set to FAKE_UUID
+
+        So, counterintuitively, we call `get` twice on the `show` command.
+        """
+        req = webob.Request.blank('/v1.0/servers/%s' % FAKE_UUID)
+        res = req.get_response(fakes.wsgi_app())
+        res_dict = json.loads(res.body)
+        self.assertEqual(res_dict['server']['id'], 1)
+        self.assertEqual(res_dict['server']['uuid'], FAKE_UUID)
+        self.assertEqual(res_dict['server']['name'], 'server1')
+
     def test_get_server_by_id_v1_1(self):
         req = webob.Request.blank('/v1.1/servers/1')
         res = req.get_response(fakes.wsgi_app())
@@ -540,7 +587,8 @@ class ServersTest(test.TestCase):
     def _setup_for_create_instance(self):
         """Shared implementation for tests below that create instance"""
         def instance_create(context, inst):
-            return {'id': '1', 'display_name': 'server_test'}
+            return {'id': 1, 'display_name': 'server_test',
+                    'uuid': FAKE_UUID}
 
         def server_update(context, id, params):
             return instance_create(context, id)
@@ -594,11 +642,22 @@ class ServersTest(test.TestCase):
         self.assertEqual(1, server['id'])
         self.assertEqual(2, server['flavorId'])
         self.assertEqual(3, server['imageId'])
+        self.assertEqual(FAKE_UUID, server['uuid'])
         self.assertEqual(res.status_int, 200)
 
     def test_create_instance(self):
         self._test_create_instance_helper()
 
+    def test_create_instance_has_uuid(self):
+        """Tests at the db-layer instead of API layer since that's where the
+           UUID is generated
+        """
+        ctxt = context.RequestContext(1, 1)
+        values = {}
+        instance = nova.db.api.instance_create(ctxt, values)
+        expected = FAKE_UUID
+        self.assertEqual(instance['uuid'], expected)
+
     def test_create_instance_via_zones(self):
         """Server generated ReservationID"""
         self._setup_for_create_instance()
@@ -1850,7 +1909,8 @@ class TestServerInstanceCreation(test.TestCase):
                     self.injected_files = kwargs['injected_files']
                 else:
                     self.injected_files = None
-                return [{'id': '1234', 'display_name': 'fakeinstance'}]
+                return [{'id': '1234', 'display_name': 'fakeinstance',
+                         'uuid': FAKE_UUID}]
 
             def set_admin_password(self, *args, **kwargs):
                 pass
diff --git a/nova/tests/scheduler/test_scheduler.py b/nova/tests/scheduler/test_scheduler.py
index 0d7929996..4be59d411 100644
--- a/nova/tests/scheduler/test_scheduler.py
+++ b/nova/tests/scheduler/test_scheduler.py
@@ -48,6 +48,10 @@ flags.DECLARE('stub_network', 'nova.compute.manager')
 flags.DECLARE('instances_path', 'nova.compute.manager')
 
 
+FAKE_UUID_NOT_FOUND = 'ffffffff-ffff-ffff-ffff-ffffffffffff'
+FAKE_UUID = 'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa'
+
+
 class TestDriver(driver.Scheduler):
     """Scheduler Driver for Tests"""
     def schedule(context, topic, *args, **kwargs):
@@ -926,12 +930,23 @@ def zone_get_all(context):
            ]
 
 
+def fake_instance_get_by_uuid(context, uuid):
+    if FAKE_UUID_NOT_FOUND:
+        raise exception.InstanceNotFound(instance_id=uuid)
+    else:
+        return {'id': 1}
+
+
 class FakeRerouteCompute(api.reroute_compute):
+    def __init__(self, method_name, id_to_return=1):
+        super(FakeRerouteCompute, self).__init__(method_name)
+        self.id_to_return = id_to_return
+
     def _call_child_zones(self, zones, function):
         return []
 
     def get_collection_context_and_id(self, args, kwargs):
-        return ("servers", None, 1)
+        return ("servers", None, self.id_to_return)
 
     def unmarshall_result(self, zone_responses):
         return dict(magic="found me")
@@ -960,6 +975,8 @@ class ZoneRedirectTest(test.TestCase):
         self.stubs = stubout.StubOutForTesting()
 
         self.stubs.Set(db, 'zone_get_all', zone_get_all)
+        self.stubs.Set(db, 'instance_get_by_uuid',
+                       fake_instance_get_by_uuid)
 
         self.enable_zone_routing = FLAGS.enable_zone_routing
         FLAGS.enable_zone_routing = True
@@ -976,8 +993,19 @@ class ZoneRedirectTest(test.TestCase):
         except api.RedirectResult, e:
             self.fail(_("Successful database hit should succeed"))
 
-    def test_trap_not_found_locally(self):
+    def test_trap_not_found_locally_id_passed(self):
+        """When an integer ID is not found locally, we cannot reroute to
+        another zone, so just return InstanceNotFound exception
+        """
         decorator = FakeRerouteCompute("foo")
+        self.assertRaises(exception.InstanceNotFound,
+            decorator(go_boom), None, None, 1)
+
+    def test_trap_not_found_locally_uuid_passed(self):
+        """When a UUID is found, if the item isn't found locally, we should
+        try to reroute to a child zone to see if they have it
+        """
+        decorator = FakeRerouteCompute("foo", id_to_return=FAKE_UUID_NOT_FOUND)
         try:
             result = decorator(go_boom)(None, None, 1)
             self.assertFail(_("Should have rerouted."))
diff --git a/nova/tests/test_utils.py b/nova/tests/test_utils.py
index 8f7e83c3e..3a3f914e4 100644
--- a/nova/tests/test_utils.py
+++ b/nova/tests/test_utils.py
@@ -275,3 +275,21 @@ class GenericUtilsTestCase(test.TestCase):
         # error case
         result = utils.parse_server_string('www.exa:mple.com:8443')
         self.assertEqual(('', ''), result)
+
+
+class IsUUIDLikeTestCase(test.TestCase):
+    def assertUUIDLike(self, val, expected):
+        result = utils.is_uuid_like(val)
+        self.assertEqual(result, expected)
+
+    def test_good_uuid(self):
+        val = 'aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa'
+        self.assertUUIDLike(val, True)
+
+    def test_integer_passed(self):
+        val = 1
+        self.assertUUIDLike(val, False)
+
+    def test_non_uuid_string_passed(self):
+        val = 'foo-fooo'
+        self.assertUUIDLike(val, False)
diff --git a/nova/utils.py b/nova/utils.py
index 691134ada..e2ac16f31 100644
--- a/nova/utils.py
+++ b/nova/utils.py
@@ -35,6 +35,7 @@ import struct
 import sys
 import time
 import types
+import uuid
 from xml.sax import saxutils
 
 from eventlet import event
@@ -726,3 +727,17 @@ def parse_server_string(server_str):
     except:
         LOG.debug(_('Invalid server_string: %s' % server_str))
         return ('', '')
+
+
+def gen_uuid():
+    return uuid.uuid4()
+
+
+def is_uuid_like(val):
+    """For our purposes, a UUID is a string in canoical form:
+
+        aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa
+    """
+    if not isinstance(val, basestring):
+        return False
+    return (len(val) == 36) and (val.count('-') == 4)