Better error reporting in Elector class.

ccserver/election.py

@@ -86,7 +86,16 @@ class Elector(object):
                     distribute = getattr(self, func)
 
         # Get the destination hypervisor candidates:
-        candidates = self._get_candidates(self.FILTERS[mtype])
+        candidates, errors = self._get_candidates(self.FILTERS[mtype])
+
+        # Check if VM migration election raised an error:
+        if errors:
+            # If errors are found, we report only the first of them, because we
+            # have currently no way to report problem for each vm:
+            vm, desc = errors[0]
+            raise ElectionError('No destination found for %r, last destination'
+                                ' filtered by %s' % (vm['id'], desc))
+
 
         # Distributes VMs to each candidate:
         migration_plan = distribute(mtype, candidates)
@@ -110,6 +119,7 @@ class Elector(object):
         hvs = self._server.list(self._query_dest, show=hv_tags)
 
         candidates = []
+        errors = []
 
         # Filters the candidates:
         for vm in vms:
@@ -121,9 +131,14 @@ class Elector(object):
             vm_dest = copy(hvs)
             for func, desc in filterfuncs:
                 vm_dest = func(vm, vm_dest)
-            candidates.append((vm, vm_dest))
+                # VM is added to errors if none destination HV is found for it:
+                if not vm_dest:
+                    errors.append((vm, desc))
+                    break
+            else:
+                candidates.append((vm, vm_dest))
 
-        return candidates
+        return candidates, errors
 
 #####
 ##### Distribution algorithm methods: