Add docs and defaults for multi-master setup

Additionally, add the lb group to contain lb nodes to the
static inventory template. Include the lb group into the
OSEv3 group, in order to apply the cluster group vars to it.

Signed-off-by: Bogdan Dobrelya <bdobreli@redhat.com>

playbooks/provisioning/openstack/README.md

@@ -162,6 +162,19 @@ The `openstack_inventory_path` points the directory to host the generated static
 It should point to the copied example inventory directory, otherwise ti creates
 a new one for you.
 
+#### Multi-master configuration
+
+Please refer to the official documentation for the
+[multi-master setup](https://docs.openshift.com/container-platform/3.6/install_config/install/advanced_install.html#multiple-masters)
+and define the corresponding [inventory
+variables](https://docs.openshift.com/container-platform/3.6/install_config/install/advanced_install.html#configuring-cluster-variables)
+in `inventory/group_vars/OSEv3.yml`. For example, given a load balancer node
+under the ansible group named `ext_lb`:
+
+    openshift_master_cluster_method: native
+    openshift_master_cluster_hostname: "{{ groups.ext_lb.0 }}"
+    openshift_master_cluster_public_hostname: "{{ groups.ext_lb.0 }}"
+
 #### Security notes
 
 Configure required `*_ingress_cidr` variables to restrict public access

playbooks/provisioning/openstack/sample-inventory/group_vars/OSEv3.yml

@@ -4,6 +4,10 @@ openshift_deployment_type: origin
 #openshift_release: v3.5
 openshift_master_default_subdomain: "apps.{{ env_id }}.{{ public_dns_domain }}"
 
+openshift_master_cluster_method: native
+openshift_master_cluster_hostname: "{{ groups.lb.0|default(groups.masters.0) }}"
+openshift_master_cluster_public_hostname: "{{ groups.lb.0|default(groups.masters.0) }}"
+
 #openshift_cluster_node_labels:
 #  app:
 #    region: primary

roles/static_inventory/templates/inventory.j2

@@ -39,6 +39,7 @@ dns
 [OSEv3:children]
 nodes
 etcd
+lb
 
 # Set variables common for all OSEv3 hosts
 #[OSEv3:vars]
@@ -68,6 +69,9 @@ nodes.{{ stack_name }}
 [dns:children]
 dns.{{ stack_name }}
 
+[lb:children]
+lb.{{ stack_name }}
+
 # Empty placeholders for all groups of the cluster nodes
 [masters.{{ stack_name }}]
 [etcd.{{ stack_name }}]
@@ -75,6 +79,7 @@ dns.{{ stack_name }}
 [nodes.{{ stack_name }}]
 [app.{{ stack_name }}]
 [dns.{{ stack_name }}]
+[lb.{{ stack_name }}]
 
 # BEGIN Autogenerated groups
 {% for group in groups %}