fail when attempting to shrink the number of instances

playbooks/edx-east/edx_service.yml

@@ -238,6 +238,10 @@
         tags: "{{ reformatted_asg_instance_tags.function_output }}"
       register: potential_existing_instances
 
+    - name: Compare requested instances vs. current instances
+      when: not auto_scaling_service and (potential_existing_instances.instances|length > create_instances | int)
+      fail: msg="This playbook will not shrink the number of instances. {{create_instances }} requested. There are currently {{ potential_existing_instances.instances|length }} instances that match this tag." 
+
     #This task will create the number of instances requested (create_instances parameter). 
     # By default, it will create instances equaling the number of subnets specified.
     #Modulo logic explained: The subnet specified will be the instance number modulo the number of subnets,