azure/net: generate_fallback_nic emits network v2 config instead of v1

The function generate_fallback_config is used by Azure by default when
not consuming IMDS configuration data. This function is also used by any
datasource which does not implement it's own network config. This simple
fallback configuration sets up dhcp on the most likely NIC. It will now
emit network v2 instead of network v1.

This is a step toward moving all components talking in v2 and allows us
to avoid costly conversions between v1 and v2 for newer distributions
which rely on netplan.

1 files changed, 11 insertions, 20 deletions

diff --git a/cloudinit/net/__init__.py b/cloudinit/net/__init__.py
index f3cec794..ea707c09 100644
--- a/cloudinit/net/__init__.py
+++ b/cloudinit/net/__init__.py
@@ -265,32 +265,23 @@ def find_fallback_nic(blacklist_drivers=None):
 
 
 def generate_fallback_config(blacklist_drivers=None, config_driver=None):
-    """Determine which attached net dev is most likely to have a connection and
-       generate network state to run dhcp on that interface"""
-
+    """Generate network cfg v2 for dhcp on the NIC most likely connected."""
     if not config_driver:
         config_driver = False
 
     target_name = find_fallback_nic(blacklist_drivers=blacklist_drivers)
-    if target_name:
-        target_mac = read_sys_net_safe(target_name, 'address')
-        nconf = {'config': [], 'version': 1}
-        cfg = {'type': 'physical', 'name': target_name,
-               'mac_address': target_mac, 'subnets': [{'type': 'dhcp'}]}
-        # inject the device driver name, dev_id into config if enabled and
-        # device has a valid device driver value
-        if config_driver:
-            driver = device_driver(target_name)
-            if driver:
-                cfg['params'] = {
-                    'driver': driver,
-                    'device_id': device_devid(target_name),
-                }
-        nconf['config'].append(cfg)
-        return nconf
-    else:
+    if not target_name:
         # can't read any interfaces addresses (or there are none); give up
         return None
+    target_mac = read_sys_net_safe(target_name, 'address')
+    cfg = {'dhcp4': True, 'set-name': target_name,
+           'match': {'macaddress': target_mac.lower()}}
+    if config_driver:
+        driver = device_driver(target_name)
+        if driver:
+            cfg['match']['driver'] = driver
+    nconf = {'ethernets': {target_name: cfg}, 'version': 2}
+    return nconf
 
 
 def extract_physdevs(netcfg):