Switch to AZAwareWeightScheduler as of Mitaka

AZAwareWeightScheduler is based on WeightScheduler and provides a way to make
DHCP agent scheduling be AZ-aware. This is used in conjunction with
dhcp-agents-per-network config option and per-network agents (such as dnsmasq)
will be distributed across neutron-dhcp-agents that have availability_zone
configuration (based on dhcp-load-type for placement calculation).

bp: https://blueprints.launchpad.net/neutron/+spec/add-availability-zone

Upgrade impact is mentioned here:
specs.openstack.org/openstack/neutron-specs/specs/mitaka/availability-zone.html

The spec mentions that by default all agents belong to 'nova' AZ so
the scheduler change should be backwards-compatible.

Change-Id: I4d948efa157573fdbc0fbfd3b1efb21b69a713ef
Closes-Bug: #1796068

config.yaml

@@ -726,3 +726,9 @@ options:
       The size in bits of the prefix for the IPv6 reverse lookup (PTR) zones.
       .
       NOTE: Use only when "reverse-dns-lookup" option is set to "True".
+  dhcp-load-type:
+    type: string
+    default: 'networks'
+    description: |
+      Sets the resource type used in weight calculations during
+      AZ-aware scheduling (networks, subnets or ports).

hooks/neutron_api_context.py

@@ -400,6 +400,7 @@ class NeutronCCContext(context.NeutronContext):
             config('allow-automatic-l3agent-failover')
         ctxt['allow_automatic_dhcp_failover'] = \
             config('allow-automatic-dhcp-failover')
+
         ctxt['dhcp_agents_per_network'] = config('dhcp-agents-per-network')
         ctxt['tenant_network_types'] = self.neutron_tenant_network_types
         ctxt['overlay_network_type'] = self.neutron_overlay_network_type
@@ -472,6 +473,13 @@ class NeutronCCContext(context.NeutronContext):
                 if related_units(rid):
                     enable_dns_extension_driver = True
 
+            # AZAwareWeightScheduler inherits from WeightScheduler and is
+            # available as of mitaka
+            ctxt['network_scheduler_driver'] = (
+                'neutron.scheduler.dhcp_agent_scheduler.AZAwareWeightScheduler'
+            )
+            ctxt['dhcp_load_type'] = config('dhcp-load-type')
+
         extension_drivers = []
         if config('enable-ml2-port-security'):
             extension_drivers.append(EXTENSION_DRIVER_PORT_SECURITY)

templates/mitaka/neutron.conf

@@ -28,6 +28,10 @@ min_l3_agents_per_router = {{ min_l3_agents_per_router }}
 
 allow_automatic_l3agent_failover = {{ allow_automatic_l3agent_failover }}
 allow_automatic_dhcp_failover = {{ allow_automatic_dhcp_failover }}
+{% if network_scheduler_driver -%}
+network_scheduler_driver = {{ network_scheduler_driver }}
+dhcp_load_type = {{ dhcp_load_type }}
+{% endif -%}
 
 {% if neutron_bind_port -%}
 bind_port = {{ neutron_bind_port }}

templates/newton/neutron.conf

@@ -28,6 +28,10 @@ min_l3_agents_per_router = {{ min_l3_agents_per_router }}
 
 allow_automatic_l3agent_failover = {{ allow_automatic_l3agent_failover }}
 allow_automatic_dhcp_failover = {{ allow_automatic_dhcp_failover }}
+{% if network_scheduler_driver -%}
+network_scheduler_driver = {{ network_scheduler_driver }}
+dhcp_load_type = {{ dhcp_load_type }}
+{% endif -%}
 
 {% if neutron_bind_port -%}
 bind_port = {{ neutron_bind_port }}

templates/ocata/neutron.conf

@@ -28,6 +28,10 @@ min_l3_agents_per_router = {{ min_l3_agents_per_router }}
 
 allow_automatic_l3agent_failover = {{ allow_automatic_l3agent_failover }}
 allow_automatic_dhcp_failover = {{ allow_automatic_dhcp_failover }}
+{% if network_scheduler_driver -%}
+network_scheduler_driver = {{ network_scheduler_driver }}
+dhcp_load_type = {{ dhcp_load_type }}
+{% endif -%}
 
 {% if neutron_bind_port -%}
 bind_port = {{ neutron_bind_port }}

templates/pike/neutron.conf

@@ -28,6 +28,10 @@ min_l3_agents_per_router = {{ min_l3_agents_per_router }}
 
 allow_automatic_l3agent_failover = {{ allow_automatic_l3agent_failover }}
 allow_automatic_dhcp_failover = {{ allow_automatic_dhcp_failover }}
+{% if network_scheduler_driver -%}
+network_scheduler_driver = {{ network_scheduler_driver }}
+dhcp_load_type = {{ dhcp_load_type }}
+{% endif -%}
 
 {% if neutron_bind_port -%}
 bind_port = {{ neutron_bind_port }}

templates/queens/neutron.conf

@@ -28,6 +28,10 @@ min_l3_agents_per_router = {{ min_l3_agents_per_router }}
 
 allow_automatic_l3agent_failover = {{ allow_automatic_l3agent_failover }}
 allow_automatic_dhcp_failover = {{ allow_automatic_dhcp_failover }}
+{% if network_scheduler_driver -%}
+network_scheduler_driver = {{ network_scheduler_driver }}
+dhcp_load_type = {{ dhcp_load_type }}
+{% endif -%}
 
 {% if neutron_bind_port -%}
 bind_port = {{ neutron_bind_port }}

templates/rocky/neutron.conf

@@ -26,6 +26,13 @@ max_l3_agents_per_router = {{ max_l3_agents_per_router }}
 min_l3_agents_per_router = {{ min_l3_agents_per_router }}
 {% endif -%}
 
+allow_automatic_l3agent_failover = {{ allow_automatic_l3agent_failover }}
+allow_automatic_dhcp_failover = {{ allow_automatic_dhcp_failover }}
+{% if network_scheduler_driver -%}
+network_scheduler_driver = {{ network_scheduler_driver }}
+dhcp_load_type = {{ dhcp_load_type }}
+{% endif -%}
+
 {% if neutron_bind_port -%}
 bind_port = {{ neutron_bind_port }}
 {% else -%}

unit_tests/test_neutron_api_context.py

@@ -492,6 +492,10 @@ class NeutronCCContextTest(CharmTestCase):
             'vni_ranges': '1001:2000',
             'extension_drivers': 'port_security',
             'service_plugins': 'router,firewall,lbaas,vpnaas,metering',
+            'network_scheduler_driver': (
+                'neutron.scheduler.dhcp_agent_scheduler'
+                '.AZAwareWeightScheduler'),
+            'dhcp_load_type': 'networks',
         }
         napi_ctxt = context.NeutronCCContext()
         self.maxDiff = None