Simplify scheduler filter additions

Add 'nova_scheduler_extra_filters' to allow operators to enable
additional scheduler filters without overriding the entire list of
filters as in [0].

This also reduces the burden on ops to maintain the list of overridden
default schedulers because of things like [1].

[0] 3886dbc40d/openstack_deploy/user_variables.yml (L51-L69)
[1] https://review.openstack.org/#/c/596502/

Change-Id: I9ab6bcbef2b496df7f6ecf11a7d8f5f7891aeeca

defaults/main.yml

@@ -311,16 +311,18 @@ nova_reserved_host_disk_mb: 2048
 
 nova_scheduler_host_subset_size: 10
 nova_scheduler_max_attempts: 5
-nova_scheduler_default_filters: >-
-  AvailabilityZoneFilter,
-  ComputeFilter,
-  AggregateNumInstancesFilter,
-  AggregateIoOpsFilter,
-  ComputeCapabilitiesFilter,
-  ImagePropertiesFilter,
-  ServerGroupAntiAffinityFilter,
-  ServerGroupAffinityFilter,
-  NUMATopologyFilter
+nova_scheduler_default_filters:
+  - AvailabilityZoneFilter
+  - ComputeFilter
+  - AggregateNumInstancesFilter
+  - AggregateIoOpsFilter
+  - ComputeCapabilitiesFilter
+  - ImagePropertiesFilter
+  - ServerGroupAntiAffinityFilter
+  - ServerGroupAffinityFilter
+  - NUMATopologyFilter
+
+nova_scheduler_extra_filters: []
 
 # This should be tuned depending on the number of compute hosts present in the
 # deployment. Large clouds may wish to disable automatic discovery by setting

releasenotes/notes/nova_filters-41739c325c0339e9.yaml

@@ -0,0 +1,11 @@
+---
+features:
+  - |
+    Added variable `nova_scheduler_extra_filters` which allows to extend
+    list of defaulted `nova_scheduler_default_filters`
+upgrade:
+  - |
+    String value of `nova_scheduler_default_filters` is converted to the list
+    At the moment there is compatability for overriden values, that are string,
+    but this support will be removed in the future releases. So deployers are
+    recommended to replace their string overrides with list ones.

templates/nova.conf.j2

@@ -274,7 +274,7 @@ discover_hosts_in_cells_interval = {{ nova_discover_hosts_in_cells_interval }}
 [filter_scheduler]
 max_io_ops_per_host = {{ nova_max_io_ops_per_host }}
 ram_weight_multiplier = {{ nova_ram_weight_multiplier }}
-enabled_filters = {{ nova_scheduler_default_filters }}
+enabled_filters = {{ _nova_scheduler_filters | join(',') }}
 host_subset_size = {{ nova_scheduler_host_subset_size }}
 tracks_instance_changes = {{ nova_scheduler_tracks_instance_changes }}
 

vars/main.yml

@@ -93,3 +93,12 @@ nova_core_files:
     owner: "root"
     group: "{{ nova_system_group_name }}"
     mode: "0640"
+
+_nova_scheduler_filters: |-
+  {% set default_filters = nova_scheduler_default_filters %}
+  {% if default_filters is not iterable and default_filters is string %}
+  {%   set filters = default_filters.split(',')  %}
+  {% else %}
+  {%   set filters = default_filters %}
+  {% endif %}
+  {{ default_filters + nova_scheduler_extra_filters }}