Count instances managed by each instance template

appengine/gce-backend/instance_group_managers.py

 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 """Utilities for operating on instance group managers."""
 
+import collections
 import logging
 
 from google.appengine.ext import ndb
 
 from components import gce
 from components import net
 from components import utils
 
 import instance_templates
 import models
@@ skipping 366 matching lines @@
               '/internal/queues/resize-instance-group',
               'resize-instance-group',
               params={
                   'key': instance_group_manager_key.urlsafe(),
               },
           ):
             logging.warning(
                 'Failed to enqueue task for InstanceGroupManager: %s',
                 instance_group_manager_key,
             )
+
+
+def count_instances():
+  """Counts the number of instances owned by each instance template.
+
+  Returns:
+    A dict mapping instance template name to count of instances.
+  """
+  # Aggregate the number of instances owned by each instance group manager
+  # created for each instance template.
+  totals = collections.defaultdict(int)
+  for instance_group_manager in models.InstanceGroupManager.query():
+    instance_template_name = instance_group_manager.key.parent().parent().id()
+    totals[instance_template_name] += len(instance_group_manager.instances)
+  return totals