Use all available headroom for autoscaling

Fixes bug 1254796

Previously, potential headroom for autoscaling group growth
or shrinkage would remain unused unless the adjustment exactly
hit the max or min size respectively.

Now, we truncate the adjustment to the upper or lower bound
in the case of an over-shoot.

Change-Id: I760be999039f7038dab77cb8b77a0f683ef56db3

Author: Eoghan Glynn

heat/engine/resources/autoscaling.py

@@ -420,12 +420,23 @@ def adjust(self, adjustment, adjustment_type='ChangeInCapacity'):
                               else math.ceil(delta))
             new_capacity = capacity + rounded
 
-        if new_capacity > int(self.properties['MaxSize']):
-            logger.warn('can not exceed %s' % self.properties['MaxSize'])
-            return
-        if new_capacity < int(self.properties['MinSize']):
-            logger.warn('can not be less than %s' % self.properties['MinSize'])
-            return
+        upper = int(self.properties['MaxSize'])
+        lower = int(self.properties['MinSize'])
+
+        if new_capacity > upper:
+            if upper > capacity:
+                logger.info(_('truncating growth to %s') % upper)
+                new_capacity = upper
+            else:
+                logger.warn(_('can not exceed %s') % upper)
+                return
+        if new_capacity < lower:
+            if lower < capacity:
+                logger.info(_('truncating shrinkage to %s') % lower)
+                new_capacity = lower
+            else:
+                logger.warn(_('can not be less than %s') % lower)
+                return
 
         if new_capacity == capacity:
             logger.debug('no change in capacity %d' % capacity)

heat/tests/test_autoscaling.py

@@ -801,7 +801,7 @@ def test_scaling_group_scale_up_failure(self):
 
         self.m.VerifyAll()
 
-    def test_scaling_group_nochange(self):
+    def test_scaling_group_truncate_adjustment(self):
         t = template_format.parse(as_template)
         stack = utils.parse_stack(t, params=self.params)
 
@@ -819,33 +819,39 @@ def test_scaling_group_nochange(self):
                          rsrc.get_instance_names())
 
         # raise above the max
+        self._stub_lb_reload(5)
+        self._stub_meta_expected(now, 'ChangeInCapacity : 4')
+        self._stub_create(3)
+        self.m.ReplayAll()
         rsrc.adjust(4)
-        self.assertEqual(['WebServerGroup-0', 'WebServerGroup-1'],
-                         rsrc.get_instance_names())
+        self._verify_instance_names(rsrc, 5)
 
         # lower below the min
-        rsrc.adjust(-2)
-        self.assertEqual(['WebServerGroup-0', 'WebServerGroup-1'],
-                         rsrc.get_instance_names())
+        self._stub_lb_reload(1)
+        self._stub_validate()
+        self._stub_meta_expected(now, 'ChangeInCapacity : -5')
+        self.m.ReplayAll()
+        rsrc.adjust(-5)
+        self._verify_instance_names(rsrc, 1)
 
         # no change
         rsrc.adjust(0)
-        self.assertEqual(['WebServerGroup-0', 'WebServerGroup-1'],
-                         rsrc.get_instance_names())
+        self._verify_instance_names(rsrc, 1)
+
         rsrc.delete()
         self.m.VerifyAll()
 
+    def _verify_instance_names(self, group, bound):
+        instance_names = group.get_instance_names()
+        self.assertEqual(len(instance_names), bound)
+        for i in xrange(bound):
+            self.assertEqual('WebServerGroup-%d' % i, instance_names[i])
+
     def _do_test_scaling_group_percent(self, decrease, lowest,
                                        increase, create, highest):
         t = template_format.parse(as_template)
         stack = utils.parse_stack(t, params=self.params)
 
-        def _verify_instance_names(bound):
-            instance_names = rsrc.get_instance_names()
-            self.assertEqual(len(instance_names), bound)
-            for i in xrange(bound):
-                self.assertEqual('WebServerGroup-%d' % i, instance_names[i])
-
         # Create initial group, 2 instances
         properties = t['Resources']['WebServerGroup']['Properties']
         properties['DesiredCapacity'] = '2'
@@ -856,7 +862,7 @@ def _verify_instance_names(bound):
         self.m.ReplayAll()
         rsrc = self.create_scaling_group(t, stack, 'WebServerGroup')
         stack.resources['WebServerGroup'] = rsrc
-        _verify_instance_names(2)
+        self._verify_instance_names(rsrc, 2)
 
         # reduce by decrease %
         self._stub_lb_reload(lowest)
@@ -865,7 +871,7 @@ def _verify_instance_names(bound):
         self._stub_validate()
         self.m.ReplayAll()
         rsrc.adjust(decrease, 'PercentChangeInCapacity')
-        _verify_instance_names(lowest)
+        self._verify_instance_names(rsrc, lowest)
 
         # raise by increase %
         self._stub_lb_reload(highest)
@@ -874,7 +880,7 @@ def _verify_instance_names(bound):
         self._stub_create(create)
         self.m.ReplayAll()
         rsrc.adjust(increase, 'PercentChangeInCapacity')
-        _verify_instance_names(highest)
+        self._verify_instance_names(rsrc, highest)
 
         rsrc.delete()