Prevent rescue for volume-backed instances

This patch prevents rescuing of volume_backed instances, by checking
for it in the API layer and raising an exception if instance on which a
rescue was attempted is volume backed.

Rescue is supposed to just be a way to log into a wayward instance
if something goes wrong with the base image that may have had some data
(logfiles etc.) and make it possible to grab that - block devices are
assumed to be accessible by re-attaching them, and are considered
persistant so no need for rescue there.

Fixes bug: #1067744
blueprint: improve-boot-from-volume

Change-Id: I8a4b1ccff7406837de3086aa413034e8e647b8fa

1 files changed, 11 insertions, 0 deletions

diff --git a/nova/compute/api.py b/nova/compute/api.py
index 83ea98c8f..dc90748a4 100644
--- a/nova/compute/api.py
+++ b/nova/compute/api.py
@@ -2142,6 +2142,14 @@ class API(base.Base):
     @check_instance_state(vm_state=[vm_states.ACTIVE, vm_states.STOPPED])
     def rescue(self, context, instance, rescue_password=None):
         """Rescue the given instance."""
+        # TODO(ndipanov): This check can be generalized as a decorator to
+        # check for valid combinations of src and dests - for now check
+        # if it's booted from volume only
+        if self.is_volume_backed_instance(context, instance, None):
+            reason = _("Cannot rescue a volume-backed instance")
+            raise exception.InstanceNotRescuable(instance_id=instance['uuid'],
+                                                 reason=reason)
+
         self.update(context,
                     instance,
                     vm_state=vm_states.ACTIVE,
@@ -2414,6 +2422,9 @@ class API(base.Base):
                 instance['uuid'])
 
     def is_volume_backed_instance(self, context, instance, bdms):
+        if not instance['image_ref']:
+            return True
+
         if bdms is None:
             bdms = self.get_instance_bdms(context, instance)