Add parameter to select resolver

When using systemd-resolver you can choose to link /etc/resolv.conf to
a "standard" resolv.conf or to a "stub-resolv.conf" that uses 127.0.0.53
resolver provided by it.

data/common.yaml

@@ -10,6 +10,7 @@ systemd::multicast_dns: ~
 systemd::dnssec: ~
 systemd::cache: false
 systemd::dns_stub_listener: ~
+systemd::use_stub_resolver: false
 systemd::manage_networkd: false
 systemd::networkd_ensure: 'running'
 systemd::manage_timesyncd: false

manifests/init.pp

@@ -42,6 +42,9 @@
 # @param dns_stub_listener
 #   Takes a boolean argument or one of "udp" and "tcp".
 #
+# @param use_stub_resolver
+#   Takes a boolean argument. When "false" (default) it uses /var/run/systemd/resolve/resolv.conf
+#   as /etc/resolv.conf. When "true", it uses /var/run/systemd/resolve/stub-resolv.conf
 # @param manage_networkd
 #   Manage the systemd network daemon
 #
@@ -74,6 +77,7 @@
   Optional[Variant[Boolean,Enum['allow-downgrade']]] $dnssec,
   Boolean                                            $cache,
   Optional[Variant[Boolean,Enum['udp','tcp']]]       $dns_stub_listener,
+  Boolean                                            $use_stub_resolver,
   Boolean                                            $manage_networkd,
   Enum['stopped','running']                          $networkd_ensure,
   Boolean                                            $manage_timesyncd,

manifests/resolved.pp

@@ -37,6 +37,10 @@
 # @param dns_stub_listener
 #   Takes a boolean argument or one of "udp" and "tcp".
 #
+# @param use_stub_resolver
+#   Takes a boolean argument. When "false" (default) it uses /var/run/systemd/resolve/resolv.conf
+#   as /etc/resolv.conf. When "true", it uses /var/run/systemd/resolve/stub-resolv.conf
+#
 class systemd::resolved (
   Enum['stopped','running'] $ensure                                = $systemd::resolved_ensure,
   Optional[Variant[Array[String],String]] $dns                     = $systemd::dns,
@@ -47,6 +51,7 @@
   Optional[Variant[Boolean,Enum['allow-downgrade']]] $dnssec       = $systemd::dnssec,
   Boolean $cache                                                   = $systemd::cache,
   Optional[Variant[Boolean,Enum['udp', 'tcp']]] $dns_stub_listener = $systemd::dns_stub_listener,
+  Boolean $use_stub_resolver                                       = $systemd::use_stub_resolver,
 ){
 
   assert_private()
@@ -62,9 +67,13 @@
     enable => $_enable_resolved,
   }
 
+  $_resolv_conf_target = $use_stub_resolver ? {
+    true    => '/run/systemd/resolve/stub-resolv.conf',
+    default => '/run/systemd/resolve/resolv.conf',
+  }
   file { '/etc/resolv.conf':
     ensure  => 'symlink',
-    target  => '/run/systemd/resolve/resolv.conf',
+    target  => $_resolv_conf_target,
     require => Service['systemd-resolved'],
   }