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

2 files changed, 40 insertions, 23 deletions

diff --git a/heat/engine/resources/autoscaling.py b/heat/engine/resources/autoscaling.py
index ee7cfbe96..35ac1fbb6 100644
--- a/heat/engine/resources/autoscaling.py
+++ b/heat/engine/resources/autoscaling.py
@@ -420,12 +420,23 @@ class AutoScalingGroup(InstanceGroup, CooldownMixin):
                               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)
diff --git a/heat/tests/test_autoscaling.py b/heat/tests/test_autoscaling.py
index 119ce747e..d47c185d8 100644
--- a/heat/tests/test_autoscaling.py
+++ b/heat/tests/test_autoscaling.py
@@ -801,7 +801,7 @@ class AutoScalingTest(HeatTestCase):
 
         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 @@ class AutoScalingTest(HeatTestCase):
                          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 @@ class AutoScalingTest(HeatTestCase):
         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 @@ class AutoScalingTest(HeatTestCase):
         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 @@ class AutoScalingTest(HeatTestCase):
         self._stub_create(create)
         self.m.ReplayAll()
         rsrc.adjust(increase, 'PercentChangeInCapacity')
-        _verify_instance_names(highest)
+        self._verify_instance_names(rsrc, highest)
 
         rsrc.delete()