cloud-init does not provide configurable network activator priority overrides

[Chad Smith]

cloud-init has two interactions with network backplanes

1. to write (or render) network configuration to the approapriate config files for the network system: systemd, netplan, network-manager, ENI, freebsd, netbsd, openbsd. This is done via cloudinit.net.renderers discovery[1]

2. optionally to bring up the network configuration via "network activation" for datasources discovered only in init boot stage after network is already up[2]

/etc/cloud/cloud.cfg allows system_info:network:renderers to configure overrides for default renderers, but not for activators. The two discovery/mechanisms don't know about each other and have separate logic to determine which is applicable on the given system.

Cloud-init should either:
 - Expose system_info: network: activators discovery priorty/order configuration in /etc/cloud/cloud.cfg*

 -- OR --

 - make activators aware of customized/overridden renderers priority from cloud.cfg and honor that priority order when discovering activators to use.

Without this feature, overridden network: renderer priority order to set network-manager as default renderer will result in cloud-init writing /etc/NetworkManager/system-connections/cloud-init-<NIC_NAME>.nmconnection but then trying to run `netplan apply` for a non-existent configuration on ubuntu Desktop installs.

References:
[1] network renderers discovery: https://github.com/canonical/cloud-init/blob/main/cloudinit/net/renderers.py#L67
[2] network activators discovery: https://github.com/canonical/cloud-init/blob/main/cloudinit/net/activators.py#L279
[3] renderer overrides honored: https://github.com/canonical/cloud-init/blob/main/cloudinit/distros/__init__.py#L122-L126
[4] No activator overrides: https://github.com/canonical/cloud-init/blob/main/cloudinit/distros/__init__.py#L246

[Chad Smith (chad.smith)]

Adding subiquity FYI for ubuntu-desktop-installer. This fix will be required from cloud-init if subiquity installer/ephemeral environment wants to override network: activators: [network-manager] in /etc/cloud/cloud.cfg.d/*cfg

[Chad Smith (chad.smith)]

Logs on a system with renderers overridden to prefer NetworkManager but activators not aware and choosing netplan.

ubuntu@ubuntu:~$ cat /etc/cloud/cloud.cfg.d/99-installer-use-network-manager.cfg
system_info:
 network:
   renderers: [network-manager]

ubuntu@ubuntu:~$ egrep 'NetworkManager|netplan|activator|renderer' /var/log/cloud-init.log
2022-07-26 16:41:20,871 - subp.py[DEBUG]: Running command ['systemctl', 'is-enabled', 'NetworkManager.service'] with allowed return codes [0] (shell=False, capture=True)
2022-07-26 16:41:20,877 - __init__.py[DEBUG]: Selected renderer 'network-manager' from priority list: ['network-manager']
2022-07-26 16:41:20,877 - util.py[DEBUG]: Writing to /etc/NetworkManager/system-connections/cloud-init-enp0s31f6.nmconnection - wb: [600] 278 bytes
2022-07-26 16:41:34,276 - subp.py[DEBUG]: Running command ['systemctl', 'is-enabled', 'NetworkManager.service'] with allowed return codes [0] (shell=False, capture=True)
2022-07-26 16:41:34,279 - __init__.py[DEBUG]: Selected renderer 'network-manager' from priority list: ['network-manager']
2022-07-26 16:41:34,279 - util.py[DEBUG]: Writing to /etc/NetworkManager/system-connections/cloud-init-enp0s31f6.nmconnection - wb: [600] 278 bytes
2022-07-26 16:41:34,279 - subp.py[DEBUG]: Running command ['systemctl', 'is-enabled', 'NetworkManager.service'] with allowed return codes [0] (shell=False, capture=True)
2022-07-26 16:41:34,282 - activators.py[DEBUG]: Using selected activator: <class 'cloudinit.net.activators.NetplanActivator'>
2022-07-26 16:41:34,282 - activators.py[DEBUG]: Attempting command ['netplan', 'apply'] for device all
2022-07-26 16:41:34,282 - subp.py[DEBUG]: Running command ['netplan', 'apply'] with allowed return codes [0] (shell=False, capture=True)

[Chad Smith (chad.smith)]

supplemental config needed above https://bugs.launchpad.net/cloud-init/+bug/1982855

[Chad Smith (chad.smith)]

upstream PR related to this bug in progress
https://github.com/canonical/cloud-init/pull/1619

[Chad Smith (chad.smith)]

upstream commit landed for this functionality
https://github.com/canonical/cloud-init/commit/6e498773bf153f7b2f5e995a2f2fe24774dd3cab

[shixuantong (sxt1001)]

The problem seems to have been resolved, we can close it.

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/4001