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[Brett Holman <1979877@xxxxxxxxxxxxxxxxxx>]

This bug is believed to be fixed in cloud-init in version 22.3. If this
is still a problem for you, please make a comment and set the state back
to New

Thank you.

** Changed in: cloud-init
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1979877

Title:
  cloud-init fails with KeyError when nameserver config and matching
  interface are present

Status in cloud-init:
  Fix Released

Bug description:
  cloud-init fails to parse network configuration with a KeyError if:

  - The configuration has a `nameservers` configuration, and
  - The configuration matches an existing interface on the machine, and
  - The configuration name does not match that interfaces name.

  Consider the following network config:

  ```
  version: 2
  ethernets:
    eth:
      match:
        macaddress: '00:11:22:33:44:55'
      addresses: [10.0.0.2/24]
      gateway4: 10.0.0.1
      nameservers: 
        addresses: [10.0.0.1]
  ```

  Now, if a device is present with the mac address 00:11:22:33:44:55,
  parsing will fail with the following stack trace:

  ```
  2022-06-25 10:26:43,657 - util.py[WARNING]: failed stage init-local
  2022-06-25 10:26:43,657 - util.py[DEBUG]: failed stage init-local
  Traceback (most recent call last):
    File "/usr/lib/python3/dist-packages/cloudinit/cmd/main.py", line 738, in status_wrapper
      ret = functor(name, args)
    File "/usr/lib/python3/dist-packages/cloudinit/cmd/main.py", line 410, in main_init
      init.apply_network_config(bring_up=bring_up_interfaces)
    File "/usr/lib/python3/dist-packages/cloudinit/stages.py", line 937, in apply_network_config
      return self.distro.apply_network_config(
    File "/usr/lib/python3/dist-packages/cloudinit/distros/__init__.py", line 231, in apply_network_config
      network_state = parse_net_config_data(netconfig)
    File "/usr/lib/python3/dist-packages/cloudinit/net/network_state.py", line 1056, in parse_net_config_data
      nsi.parse_config(skip_broken=skip_broken)
    File "/usr/lib/python3/dist-packages/cloudinit/net/network_state.py", line 278, in parse_config
      self.parse_config_v2(skip_broken=skip_broken)
    File "/usr/lib/python3/dist-packages/cloudinit/net/network_state.py", line 328, in parse_config_v2
      self._v2_common(command)
    File "/usr/lib/python3/dist-packages/cloudinit/net/network_state.py", line 782, in _v2_common
      self._handle_individual_nameserver(name_cmd, iface)
    File "/usr/lib/python3/dist-packages/cloudinit/net/network_state.py", line 110, in decorator
      return func(self, command, *args, **kwargs)
    File "/usr/lib/python3/dist-packages/cloudinit/net/network_state.py", line 570, in _handle_individual_nameserver
      _iface[iface]["dns"] = {"nameservers": nameservers, "search": search}
  KeyError: 'eth'
  ```

  I've investigated the issue myself and created a test case:

  ```
  from unittest import mock

  from cloudinit import safeyaml
  from cloudinit.net import network_state

  
  class TestNetDns:
      @mock.patch("cloudinit.net.network_state.get_interfaces_by_mac")
      def test_networkd_render_x(self, by_mac):
          by_mac.return_value = {"00:11:22:33:44:55": "foobar"}
          network_state.parse_net_config_data(safeyaml.load("""\
  version: 2
  ethernets:
    eth:
      match:
        macaddress: '00:11:22:33:44:55'
      addresses: [10.0.0.2/24]
      gateway4: 10.0.0.1
      nameservers: 
        addresses: [10.0.0.1]
  """))
  ```

  This test case will fail with the KeyError.

  The reason for this bug is that `handle_ethernets` will take the
  interface name from the system because no set-name setting is present.
  It will then add the network state under that interface name, not the
  configured key 'eth'. Later, _handle_individual_nameserver will try to
  look up the state for 'eth' and fail.

  A quick bisect shows that this test case starts failing with commit
  bf94945fb855c40c5188cef5fb00327c51c41fef (though the mock doesn't work
  very far in the past). This commit introduced the name handling logic.

  As a workaround, you can give an explicit set-name statement, or
  change the key of the network config to match the physical device
  name.

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