Add dummy0 interface

The netplan version we have is too old to do this so handle it manually.

global/overlay/etc/puppet/modules/cdn/manifests/cache.pp

@@ -39,6 +39,14 @@ class cdn::cache(
     content => template('cdn/cache/varnish-slash-seccomp.json.erb'),
   }
 
+  file { '/etc/systemd/network/cdn-dummy.netdev':
+    ensure  => file,
+    owner   => 'root',
+    group   => 'root',
+    mode    => '0644',
+    content => template('cdn/cache/cdn-dummy.netdev.erb'),
+  }
+
   $sysctl_file = '/etc/sysctl.d/99-cdn-cache.conf'
   file { $sysctl_file:
     ensure  => file,

global/overlay/etc/puppet/modules/cdn/templates/cache/cdn-dummy.netdev.erb

@@ -0,0 +1,3 @@
+[NetDev]
+Name=dummy0
+Kind=dummy