Increase minimum Ansible version to '2.6'.

* add ansible version check to role prerequisites
* add requirements.txt
* update Readme.md
* track minimum ansible version in variable 'ansible_version_minimum'

Readme.md

@@ -18,7 +18,7 @@ Playbook eingebunden sein.
 Voraussetzungen für die Control Machine:
 
 - Python 2 (Versionen 2.6 oder 2.7) oder 3 (Versionen 3.5 oder höher)
-- Ansible Version >= 2.5
+- Ansible Version >= 2.6
 - Python Modul `netaddr`
 - Python Modul `dnspython`
 

inventory/group_vars/all

@@ -1,4 +1,5 @@
 ---
+ansible_version_minimum: "2.6"
 debug_fastd: False
 
 as_private_mwu: 65037

requirements.txt

@@ -0,0 +1,3 @@
+ansible>=2.6
+netaddr>=0.7.19
+dnspython>=1.15.0

roles/prerequisites/tasks/main.yml

@@ -1,4 +1,9 @@
 ---
+- name: Check for minimal Ansible version
+  assert:
+    that: "ansible_version.full is version_compare(ansible_version_minimum, '>=')"
+    msg: "You must update Ansible to at least version {{ ansible_version_minimum }}."
+  run_once: True
 
 - name: Check basic DNS entries and target distribution
   assert: