Update example playbook to support both underscores and hyphens in group names

As of Ansible 2.8, group names containing "-" (hyphen) characters are
considered invalid, and will generate a warning about
TRANSFORM_INVALID_GROUP_CHARS.

Thus, give users the ability to gradually change over their group
names by supporting both the "taiga-*" and "taiga_*" group name
patterns.

Also, update the README accordingly.

README.md

@@ -82,8 +82,17 @@ taiga-events.example.com
 ## Playbooks
 
 An example playbook is provided in `taiga.yml`. It understands the
-group names `taiga-back`, `taiga-front`, and `taiga-events`, and maps
-them to the roles of the same name.
+group names `taiga_back`, `taiga_front`, and `taiga_events`, and maps
+them to the corresponding role names.
+
+Note that the example playbook also understands the group names
+`taiga-back`, `taiga-front`, and `taiga-events`, using hyphens instead
+of underscores. Running a playbook with hyphens in group names is
+deprecated and will raise a warning in Ansible version 2.8 and
+later. Starting with Ansible 2.10, hyphens in group names are no
+longer supported — so if you use the example playbook verbatim, or use
+your own playbook with hyphens in group names, please update your
+inventory to correct your group names.
 
 ## Variables
 

roles/taiga/defaults/main.yml

 ---
 # Which host runs our backend?
-taiga_backend_host: "{{ hostvars[groups['taiga-back'][0]]['ansible_fqdn'] }}"
+taiga_backend_host: "{{ hostvars[groups['taiga_back'][0]]['ansible_fqdn'] }}"
 
 # Which host should run the taiga-events service?
-taiga_events_host: "{{ hostvars[groups['taiga-events'][0]]['ansible_fqdn'] }}"
+taiga_events_host: "{{ hostvars[groups['taiga_events'][0]]['ansible_fqdn'] }}"
 
 # Which host should run the Taiga front end?
-taiga_frontend_host: "{{ hostvars[groups['taiga-front'][0]]['ansible_fqdn'] }}"
+taiga_frontend_host: "{{ hostvars[groups['taiga_front'][0]]['ansible_fqdn'] }}"
 
 # Which user should be created on all hosts for Taiga's own purposes?
 # Taiga services must not be run as root.

roles/taiga/tasks/main.yml

@@ -34,9 +34,9 @@
 
 - name: set facts identifying node roles
   set_fact:
-    _taiga_is_back_node: "{{ ('taiga-back' in group_names) | bool | default(false) }}"
-    _taiga_is_front_node: "{{ ('taiga-front' in group_names) | bool | default(false) }}"
-    _taiga_is_events_node: "{{ ('taiga-events' in group_names) | bool | default(false) }}"
+    _taiga_is_back_node: "{{ ('taiga_back' in group_names) | bool | default(false) }}"
+    _taiga_is_front_node: "{{ ('taiga_front' in group_names) | bool | default(false) }}"
+    _taiga_is_events_node: "{{ ('taiga_events' in group_names) | bool | default(false) }}"
   tags:
     - always
 

taiga.yml

 - hosts:
     - taiga-front
+    - taiga_front
     - taiga-back
+    - taiga_back
     - taiga-events
+    - taiga_events
   become: false
   tasks:
     - name: group hosts by distribution
       group_by:
-        key: "{{ ansible_distribution | lower }}-{{ ansible_distribution_release | lower }}"
+        key: "{{ ansible_distribution | lower }}_{{ ansible_distribution_release | lower }}"
       changed_when: false
   tags:
     - always
 
-- hosts: taiga-back
+- hosts:
+    - taiga-back
+  become: false
+  tasks:
+    - name: map taiga-back to taiga_back
+      group_by:
+        key: 'taiga_back'
+      changed_when: false
+  gather_facts: false
+  tags:
+    - always
+
+- hosts:
+    - taiga-front
+  become: false
+  tasks:
+    - name: map taiga-front to taiga_front
+      group_by:
+        key: 'taiga_front'
+      changed_when: false
+  gather_facts: false
+  tags:
+    - always
+
+- hosts:
+    - taiga-events
+  become: false
+  tasks:
+    - name: map taiga-events to taiga_events
+      group_by:
+        key: 'taiga_events'
+      changed_when: false
+  gather_facts: false
+  tags:
+    - always
+
+- hosts:
+    - taiga_back
   roles:
     - role: taiga-back
 
-- hosts: taiga-events
+- hosts:
+    - taiga_events
   roles:
     - role: taiga-events
 
-- hosts: taiga-front
+- hosts:
+    - taiga_front
   roles:
     - role: taiga-front

variables.md

@@ -5,13 +5,13 @@
 ```yaml
 ---
 # Which host runs our backend?
-taiga_backend_host: "{{ hostvars[groups['taiga-back'][0]]['ansible_fqdn'] }}"
+taiga_backend_host: "{{ hostvars[groups['taiga_back'][0]]['ansible_fqdn'] }}"
 
 # Which host should run the taiga-events service?
-taiga_events_host: "{{ hostvars[groups['taiga-events'][0]]['ansible_fqdn'] }}"
+taiga_events_host: "{{ hostvars[groups['taiga_events'][0]]['ansible_fqdn'] }}"
 
 # Which host should run the Taiga front end?
-taiga_frontend_host: "{{ hostvars[groups['taiga-front'][0]]['ansible_fqdn'] }}"
+taiga_frontend_host: "{{ hostvars[groups['taiga_front'][0]]['ansible_fqdn'] }}"
 
 # Which user should be created on all hosts for Taiga's own purposes?
 # Taiga services must not be run as root.