Fix deleting clusters if stack is deleted

If a stack has been deleted (either by Magnum or the user) but
Magnum did not update and set `stack_id` to empty, the cluster
will fail to delete inside pre-deletion.

This will have a safe failover to skip if it can't find the
Heat stack, it assumes things are gone.

Change-Id: I6ebe188895e51ed83ad1514a380e4772fed5eb42

Author: mnaser

magnum/common/octavia.py

@@ -14,6 +14,7 @@
 import re
 import time
 
+import heatclient.exc as heat_exc
 from osc_lib import exceptions as osc_exc
 from oslo_config import cfg
 from oslo_log import log as logging
@@ -106,9 +107,14 @@ def delete_loadbalancers(context, cluster):
 
         # Get load balancers created for Kubernetes api/etcd
         lbs = []
-        lb_resources = heat_client.resources.list(
-            cluster.stack_id, nested_depth=2,
-            filters={"type": lb_resource_type})
+        try:
+            lb_resources = heat_client.resources.list(
+                cluster.stack_id, nested_depth=2,
+                filters={"type": lb_resource_type})
+        except heat_exc.HTTPNotFound:
+            # NOTE(mnaser): It's possible that the stack has been deleted
+            #               but Magnum still has a `stack_id` pointing.
+            return
         for lb_res in lb_resources:
             lb_id = lb_res.physical_resource_id
             if not lb_id:

magnum/tests/unit/common/test_octavia.py

@@ -14,6 +14,8 @@
 
 from unittest import mock
 
+import heatclient.exc as heat_exc
+
 from magnum.common import exception
 from magnum.common import octavia
 from magnum import objects
@@ -169,3 +171,26 @@ def test_delete_loadbalancers_already_deleted(self, mock_clients,
 
         self.assertFalse(mock_octavia_client.load_balancer_show.called)
         self.assertFalse(mock_octavia_client.load_balancer_delete.called)
+
+    @mock.patch("magnum.common.neutron.delete_floatingip")
+    @mock.patch('magnum.common.clients.OpenStackClients')
+    def test_delete_loadbalancers_with_stack_not_found(self, mock_clients,
+                                                       mock_delete_fip):
+        mock_octavia_client = mock.MagicMock()
+        mock_octavia_client.load_balancer_list.return_value = {
+            "loadbalancers": []
+        }
+
+        mock_heat_client = mock.MagicMock()
+        mock_heat_client.resources.list.side_effect = \
+            heat_exc.HTTPNotFound
+
+        osc = mock.MagicMock()
+        mock_clients.return_value = osc
+        osc.octavia.return_value = mock_octavia_client
+        osc.heat.return_value = mock_heat_client
+
+        octavia.delete_loadbalancers(self.context, self.cluster)
+
+        self.assertFalse(mock_octavia_client.load_balancer_show.called)
+        self.assertFalse(mock_octavia_client.load_balancer_delete.called)