Handle global dns entries in netplan

In network config v1 format, there are dns values which are not bound to a
specific interface and do not map to the per-interface format in netplan.
To handle this case we render netplan configuration that duplicates the
DNS configuration on any interface that has a static network config.  We
avoiding interfaces which have DHCP configuration which may provide
conflicting DNS values.

LP: #1750884

1 files changed, 9 insertions, 16 deletions

diff --git a/cloudinit/net/netplan.py b/cloudinit/net/netplan.py
index 6bee3d37..63443484 100644
--- a/cloudinit/net/netplan.py
+++ b/cloudinit/net/netplan.py
@@ -336,22 +336,15 @@ class Renderer(renderer.Renderer):
                 _extract_addresses(ifcfg, vlan)
                 vlans.update({ifname: vlan})
 
-        # inject global nameserver values under each physical interface
-        if nameservers:
-            for _eth, cfg in ethernets.items():
-                nscfg = cfg.get('nameservers', {})
-                addresses = nscfg.get('addresses', [])
-                addresses += nameservers
-                nscfg.update({'addresses': addresses})
-                cfg.update({'nameservers': nscfg})
-
-        if searchdomains:
-            for _eth, cfg in ethernets.items():
-                nscfg = cfg.get('nameservers', {})
-                search = nscfg.get('search', [])
-                search += searchdomains
-                nscfg.update({'search': search})
-                cfg.update({'nameservers': nscfg})
+        # inject global nameserver values under each all interface which
+        # has addresses and do not already have a DNS configuration
+        if nameservers or searchdomains:
+            nscfg = {'addresses': nameservers, 'search': searchdomains}
+            for section in [ethernets, wifis, bonds, bridges, vlans]:
+                for _name, cfg in section.items():
+                    if 'nameservers' in cfg or 'addresses' not in cfg:
+                        continue
+                    cfg.update({'nameservers': nscfg})
 
         # workaround yaml dictionary key sorting when dumping
         def _render_section(name, section):