Don't pile up successive full refreshes during AWS scaledowns

Force refreshing everything at every DeleteNodes calls causes slow down
and throttling on large clusters with many ASGs (and lot of activity).

That function might be called several times in a row during scale-down
(once for each ASG having a node to be removed). Each time the forced
refresh will re-discover all ASGs, all LaunchConfigurations, then re-list all
instances from discovered ASGs.

That immediate refresh isn't required anyway, as the cache's DeleteInstances
concrete implementation will decrement the nodegroup size, and we can
schedule a grouped refresh for the next loop iteration.

cluster-autoscaler/cloudprovider/aws/aws_cloud_provider_test.go

@@ -469,7 +469,7 @@ func TestDeleteNodes(t *testing.T) {
 	err = asgs[0].DeleteNodes([]*apiv1.Node{node})
 	assert.NoError(t, err)
 	service.AssertNumberOfCalls(t, "TerminateInstanceInAutoScalingGroup", 1)
-	service.AssertNumberOfCalls(t, "DescribeAutoScalingGroupsPages", 2)
+	service.AssertNumberOfCalls(t, "DescribeAutoScalingGroupsPages", 1)
 
 	newSize, err := asgs[0].TargetSize()
 	assert.NoError(t, err)
@@ -516,7 +516,7 @@ func TestDeleteNodesWithPlaceholder(t *testing.T) {
 	err = asgs[0].DeleteNodes([]*apiv1.Node{node})
 	assert.NoError(t, err)
 	service.AssertNumberOfCalls(t, "SetDesiredCapacity", 1)
-	service.AssertNumberOfCalls(t, "DescribeAutoScalingGroupsPages", 2)
+	service.AssertNumberOfCalls(t, "DescribeAutoScalingGroupsPages", 1)
 
 	newSize, err := asgs[0].TargetSize()
 	assert.NoError(t, err)

cluster-autoscaler/cloudprovider/aws/aws_manager.go

@@ -294,8 +294,9 @@ func (m *AwsManager) DeleteInstances(instances []*AwsInstanceRef) error {
 	if err := m.asgCache.DeleteInstances(instances); err != nil {
 		return err
 	}
-	klog.V(2).Infof("Some ASG instances might have been deleted, forcing ASG list refresh")
-	return m.forceRefresh()
+	klog.V(2).Infof("Some ASG instances might have been deleted, scheduling an ASG list refresh")
+	m.lastRefresh = time.Now().Add(-refreshInterval)
+	return nil
 }
 
 // GetAsgNodes returns Asg nodes.