"dhcp_agents_per_network" parameter is set depending on number of controller node count.

Issue

• I deployed RHOS setup with composable roles. I separated neutron from controller node.

- 1 controller node
- 2 neutron nodes
- 1 compute node

• But, after deployment when I created network/subnet, I can see only one instance of DHCP instead of two. According to setup, as I have deployed two neutron nodes, there should be two instances of DHCP process per subnet.

[stack@instack ~]$ source stackrc 
[stack@instack ~]$ nova list
+--------------------------------------+------------------------+--------+------------+-------------+---------------------+
| ID                                   | Name                   | Status | Task State | Power State | Networks            |
+--------------------------------------+------------------------+--------+------------+-------------+---------------------+
| b458e6de-77cb-42c1-a065-5af279632574 | overcloud-compute-0    | ACTIVE | -          | Running     | ctlplane=192.0.2.6  |
| 29aa6302-514f-4ba4-a900-0baca1f34014 | overcloud-controller-0 | ACTIVE | -          | Running     | ctlplane=192.0.2.11 |
| bb703842-16de-4779-8634-2a616e231552 | overcloud-network-0    | ACTIVE | -          | Running     | ctlplane=192.0.2.9  |
| 1d1a6374-8f23-426f-a46c-b2d215a228bc | overcloud-network-1    | ACTIVE | -          | Running     | ctlplane=192.0.2.16 |
+--------------------------------------+------------------------+--------+------------+-------------+---------------------+

[stack@instack ~]$ source overcloudrc 
[stack@instack ~]$ neutron net-show internal
+---------------------------+--------------------------------------+
| Field                     | Value                                |
+---------------------------+--------------------------------------+
| admin_state_up            | True                                 |
| availability_zone_hints   |                                      |
| availability_zones        | nova                                 |
| created_at                | 2016-12-20T19:13:56Z                 |
| description               |                                      |
| id                        | f4bb338a-5aa0-4e28-97ef-3b65b47128f9 |
| ipv4_address_scope        |                                      |
| ipv6_address_scope        |                                      |
| mtu                       | 1446                                 |
| name                      | internal                             |
| port_security_enabled     | True                                 |
| project_id                | 5ecb362323464f6699115dc4a7772834     |
| provider:network_type     | vxlan                                |
| provider:physical_network |                                      |
| provider:segmentation_id  | 65                                   |
| qos_policy_id             |                                      |
| revision_number           | 5                                    |
| router:external           | False                                |
| shared                    | False                                |
| status                    | ACTIVE                               |
| subnets                   | e1d5ab66-b308-4883-8755-d964d3f4fd3f |
| tags                      |                                      |
| tenant_id                 | 5ecb362323464f6699115dc4a7772834     |
| updated_at                | 2016-12-20T19:14:12Z                 |
+---------------------------+--------------------------------------+

[stack@instack ~]$ neutron dhcp-agent-list-hosting-net internal
+--------------------------------------+---------------------------------+----------------+-------+
| id                                   | host                            | admin_state_up | alive |
+--------------------------------------+---------------------------------+----------------+-------+
| 2f937568-fe62-4183-8831-f014549b6c62 | overcloud-network-1.localdomain | True           | :-)   |
+--------------------------------------+---------------------------------+----------------+-------+

• From neutron node:

[root@overcloud-network-0 heat-admin]# egrep -i dhcp_ /etc/neutron/neutron.conf  |egrep -v '#'
dhcp_agents_per_network=1  <===

• NeutronDhcpAgentsPerNetwork should be automatically generated based on the number of nodes which run the NeutronDhcpAgent services.