Since the Kilo release of OpenStack, many advanced service configuration options have moved out of the main Neutron configuration file into their own files. On the controller01 node, create or update the Neutron LBaaS configuration file at /etc/neutron/neutron_lbaas.conf and define the HAProxy service provider driver for LBaaS:

[service_providers] 
... 
service_provider = LOADBALANCERV2:Haproxy:neutron_lbaas.drivers.haproxy.plugin_driver.HaproxyOnHostPluginDriver:default