Allow resolv.conf configuration to be prevented

In some cases we may wish to use an existing DNS resolver configuration, or to
acquire the configuration via a protocol such as DHCP. In these cases the
variable resolv_is_managed should be set to false.

Change-Id: I1e4661f3eedd87da15142d2d6815aaeb0493be6c
Story: 2001967
Task: 15718

ansible/group_vars/all/dns

@@ -2,6 +2,9 @@
 ###############################################################################
 # DNS.
 
+# Whether kayobe should configure resolv.conf.
+resolv_is_managed: true
+
 # List of DNS nameservers.
 resolv_nameservers:
   - 8.8.8.8

ansible/network.yml

@@ -50,6 +50,7 @@
 
   roles:
     - role: ahuffman.resolv
+      when: resolv_is_managed | bool
       become: True
 
     - role: MichaelRigart.interfaces

doc/source/configuration/network.rst

@@ -368,6 +368,25 @@ VLAN to be forwarded by the bridge, whereas adding a VLAN interface to an
 Ethernet or bond interface that is a bridge member port will prevent tagged
 traffic for that VLAN being forwarded by the bridge.
 
+Domain Name Service (DNS) Resolver Configuration
+================================================
+
+Kayobe supports configuration of hosts' DNS resolver via ``resolv.conf``.  DNS
+configuration should be added to ``dns.yml``.  For example:
+
+.. code-block:: yaml
+   :caption: ``dns.yml``
+
+   resolv_nameservers:
+     - 8.8.8.8
+     - 8.8.4.4
+   resolv_domain: example.com
+   resolv_search:
+     - kayobe.example.com
+
+It is also possible to prevent kayobe from modifying ``resolv.conf`` by setting
+``resolv_is_managed`` to ``false``.
+
 Network Role Configuration
 ==========================
 

etc/kayobe/dns.yml

@@ -2,6 +2,9 @@
 ###############################################################################
 # DNS.
 
+# Whether kayobe should configure resolv.conf.
+#resolv_is_managed:
+
 # List of DNS nameservers.
 #resolv_nameservers:
 

releasenotes/notes/prevent-resolv.conf-4a09d50f60f3fe28.yaml

+---
+features:
+  - Adds the ability to prevent configuration of the DNS resolver. This can be
+    done by setting ``resolv_is_managed`` to ``false``.