Added a comment to explain what's going on with kolla_nova_compute_ironic_host

ansible/group_vars/all/nova

@@ -5,3 +5,7 @@
 # Which group to use to deploy the nova-compute services for ironic. By default
 # all hosts in the nova group are used - typically the controllers.
 kolla_nova_compute_ironic_group: nova
+
+# Which host to use to deploy the nova-compute services for ironic. By default
+# this is none and the kolla_nova_compute_ironic_group is used instead.
+kolla_nova_compute_ironic_host:

ansible/roles/kolla-ansible/defaults/main.yml

@@ -210,12 +210,14 @@ kolla_openstack_logging_debug:
 # Nova options
 #######################
 
-kolla_nova_compute_ironic_host:
-
 # Which group to use to deploy the nova-compute services for ironic. By default
 # all hosts in the nova group are used - typically the controllers.
 kolla_nova_compute_ironic_group: nova
 
+# Which host to use to deploy the nova-compute services for ironic. By default
+# this is none and the kolla_nova_compute_ironic_group is used instead.
+kolla_nova_compute_ironic_host:
+
 ###############################################################################
 # Extra free-form configuraton.