Cap the number of worker threads

Users can configure the number of worker threads however when it's
not specified the calculated number of workers can get too large on
hosts with a large number of CPUs.

Change-Id: I86990deffcf9c29d39190defb0e2178a39de2aba

defaults/main.yml

@@ -108,6 +108,10 @@ ceilometer_service_in_ldap: false
 # ceilometer_collector_workers: 1
 # ceilometer_notification_workers: 1
 
+## Cap the maximum number of threads / workers when a user value is unspecified.
+ceilometer_api_threads_max: 16
+ceilometer_api_threads: "{{ [[ansible_processor_vcpus|default(2) // 2, 1] | max, ceilometer_api_threads_max] | min }}"
+
 # Enable/Disable Ceilometer per service
 glance_ceilometer_enabled: false
 nova_ceilometer_enabled: false

releasenotes/notes/capping_ceilometer_workers-80a768e3aaed0aec.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - Capping the default value for the variables
+    ``ceilometer_api_workers`` and ``ceilometer_notification_workers`` to
+    16 when the user doesn't configure these variables. Default value is half
+    the number of vCPUs available on the machine with a capping value of 16.

templates/ceilometer.conf.j2

@@ -1,8 +1,5 @@
 #{{ ansible_managed}}
 
-{% set _workers = ansible_processor_vcpus|default(2) // 2 %}
-{% set workers = _workers if _workers > 0 else 1 %}
-
 [DEFAULT]
 # Disable stderr logging
 use_stderr = False
@@ -33,7 +30,7 @@ rabbit_use_ssl = {{ ceilometer_rabbitmq_use_ssl }}
 
 [api]
 gnocchi_is_enabled = {{ ceilometer_gnocchi_enabled | bool }}
-workers = {{ ceilometer_api_workers | default(workers) }}
+workers = {{ ceilometer_api_workers | default(ceilometer_api_threads) }}
 port = 8777
 
 [collector]
@@ -44,7 +41,7 @@ batch_timeout = 5
 {% endif %}
 
 [notification]
-workers = {{ ceilometer_notification_workers | default(workers) }}
+workers = {{ ceilometer_notification_workers | default(ceilometer_api_threads) }}
 store_events = {{ not ceilometer_gnocchi_enabled | bool }}
 
 # Notification queues to listen on