Dynamically determine whether Neutron Agents should be enabled

Both the Nuage and PLUMgrid configuration guides advocate overwriting
the entire neutron_services dict in order to disable the DHCP,
Metadata and LinuxBridge Agents. This method is prone to error and
should ideally be more dynamic.

This patch implements a more dynamic approach based on the
neutron_plugin_type and the neutron_ml2_mechanism_drivers that are
set.

This will hopefully simplify the configuration of these and other
ML2 mechanisms (eg: openvswitch) when they're implemented.

Change-Id: I38e1fad4dfae24b32f4370b3da16561c42cd670d

defaults/main.yml

@@ -130,7 +130,7 @@ neutron_services:
  neutron-dhcp-agent:
    group: neutron_dhcp_agent
    service_name: neutron-dhcp-agent
-   service_en: True
+   service_en: "{{ neutron_dhcp | bool }}"
    service_conf: dhcp_agent.ini
    service_group: neutron_agent
    service_rootwrap: rootwrap.d/dhcp.filters
@@ -140,7 +140,7 @@ neutron_services:
  neutron-linuxbridge-agent:
    group: neutron_linuxbridge_agent
    service_name: neutron-linuxbridge-agent
-   service_en: True
+   service_en: "{{ neutron_linuxbridge | bool }}"
    service_conf: plugins/ml2/linuxbridge_agent.ini
    service_group: neutron_linuxbridge_agent
    service_rootwrap: rootwrap.d/linuxbridge-plugin.filters
@@ -150,7 +150,7 @@ neutron_services:
  neutron-metadata-agent:
    group: neutron_metadata_agent
    service_name: neutron-metadata-agent
-   service_en: True
+   service_en: "{{ neutron_metadata | bool }}"
    service_conf: metadata_agent.ini
    service_group: neutron_agent
    config_options: --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/metadata_agent.ini
@@ -159,7 +159,7 @@ neutron_services:
  neutron-metering-agent:
    group: neutron_metering_agent
    service_name: neutron-metering-agent
-   service_en: "{{ neutron_metering }}"
+   service_en: "{{ neutron_metering | bool }}"
    service_conf: metering_agent.ini
    service_group: neutron_agent
    config_options: --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/metering_agent.ini
@@ -168,7 +168,7 @@ neutron_services:
  neutron-l3-agent:
    group: neutron_l3_agent
    service_name: neutron-l3-agent
-   service_en: "{{ neutron_l3 }}"
+   service_en: "{{ neutron_l3 | bool }}"
    service_conf: l3_agent.ini
    service_group: neutron_agent
    service_rootwrap: rootwrap.d/l3.filters
@@ -178,7 +178,7 @@ neutron_services:
  neutron-lbaas-agent:
    group: neutron_lbaas_agent
    service_name: neutron-lbaas-agent
-   service_en: "{{ neutron_lbaas }}"
+   service_en: "{{ neutron_lbaas | bool }}"
    service_conf: lbaas_agent.ini
    service_group: neutron_agent
    service_rootwrap: rootwrap.d/lbaas-haproxy.filters
@@ -188,7 +188,7 @@ neutron_services:
  neutron-lbaasv2-agent:
    group: neutron_lbaas_agent
    service_name: neutron-lbaasv2-agent
-   service_en: "{{ neutron_lbaasv2 }}"
+   service_en: "{{ neutron_lbaasv2 | bool }}"
    service_conf: lbaas_agent.ini
    service_group: neutron_agent
    service_rootwrap: rootwrap.d/lbaas-haproxy.filters
@@ -198,7 +198,7 @@ neutron_services:
  neutron-vpnaas-agent:
    group: neutron_l3_agent
    service_name: neutron-vpnaas-agent
-   service_en: "{{ neutron_vpnaas }}"
+   service_en: "{{ neutron_vpnaas | bool }}"
    service_conf: vpnaas_agent.ini
    service_group: neutron_agent
    service_rootwrap: rootwrap.d/vpnaas.filters
@@ -212,6 +212,15 @@ neutron_services:
    service_group: neutron_server
    config_options: "--config-file /etc/neutron/neutron.conf --config-file /etc/neutron/{{ neutron_plugins[neutron_plugin_type].plugin_ini }}"
 
+## Neutron DHCP Agent
+neutron_dhcp: "{% if neutron_plugin_type == 'ml2' %}True{% else %}False{% endif %}"
+
+## Neutron Metadata Agent
+neutron_metadata: "{% if neutron_plugin_type == 'ml2' %}True{% else %}False{% endif %}"
+
+## Neutron LinuxBridge Agent
+neutron_linuxbridge: "{% if neutron_plugin_type == 'ml2' and 'linuxbridge' in neutron_ml2_mechanism_drivers %}True{% else %}False{% endif %}"
+
 ## Neutron LBaaS
 # See documentation section titled "Configuring the Network Load Balacing
 # Service (Optional)" for more details.

releasenotes/notes/neutron-agent-dynamic-enable-47f0c709ef0dfe55.yaml

@@ -0,0 +1,15 @@
+---
+features:
+  - Whether the Neutron DHCP Agent, Metadata Agent or LinuxBridge Agent
+    should be enabled is now dynamically determined based on the
+    ``neutron_plugin_type`` and the ``neutron_ml2_mechanism_drivers``
+    that are set. This aims to simplify the configuration of Neutron
+    services and eliminate the need for deployers to override the
+    entire ``neutron_services`` dict variable to disable these services.
+upgrade:
+  - Whether the Neutron DHCP Agent, Metadata Agent or LinuxBridge Agent
+    should be enabled is now dynamically determined based on the
+    ``neutron_plugin_type`` and the ``neutron_ml2_mechanism_drivers``
+    that are set. This aims to simplify the configuration of Neutron
+    services and eliminate the need for deployers to override the
+    entire ``neutron_services`` dict variable to disable these services.