Implement tunable Ceilometer workers

This patch introduces an override for the number of Ceilometer workers:
 - ceilometer_api_workers
 - ceilometer_collector_workers
 - ceilometer_notification_workers

The values may be set in /etc/openstack_deploy/user_variables.yml
and if they are unset, half the number of available vCPU's will be
used instead.

Backport Note:
The var locations were changed in the following patch and apply to
Liberty+ only:
 - https://review.openstack.org/209333

Implements: blueprint gate-split
Change-Id: I126d735b737237cde27dde8a864e945d037e2e4a

defaults/main.yml

@@ -79,6 +79,10 @@ ceilometer_service_adminuri: "{{ ceilometer_service_proto }}://{{ internal_lb_vi
 ceilometer_service_adminurl: "{{ ceilometer_service_adminuri }}"
 
 ## Ceilometer config
+# If the following variables are unset in user_variables, the value set will be half the number of available VCPUs
+# ceilometer_api_workers: 1
+# ceilometer_collector_workers: 1
+# ceilometer_notification_workers: 1
 
 # Common apt packages
 ceilometer_apt_packages:

templates/ceilometer.conf.j2

@@ -1,8 +1,10 @@
 #{{ ansible_managed}}
 
+{% set _workers = ansible_processor_vcpus|default(2) // 2 %}
+{% set workers = _workers if _workers > 0 else 1 %}
+
 [DEFAULT]
 auth_strategy = keystone
-collector_workers = 10
 notification_topics = notifications
 rpc_backend = rabbit
 
@@ -19,8 +21,15 @@ rabbit_hosts = {{ rabbitmq_servers }}
 rabbit_use_ssl = {{ rabbitmq_use_ssl }}
 
 [api]
+workers = {{ ceilometer_api_workers | default(workers) }}
 port = 8777
 
+[collector]
+workers = {{ ceilometer_collector_workers | default(workers) }}
+
+[notification]
+workers = {{ ceilometer_notification_workers | default(workers) }}
+
 [database]
 metering_connection = {{ ceilometer_connection_string }}
 event_connection = {{ ceilometer_connection_string }}