All interfaces inside juju-provisioned machine become unmanaged after upgrade to 106

[Boris Lukashev]

Upgrading juju-managed Ceph and seeing the containers (mons & rgws) fail to bring up networking after the update. Netplan apply now throws a bunch of warnings re permissions and gateway4 which i resolved by chmod 600 for the netplan config file and replacement of the gateway4 key with the new routes section... but interfaces _still_ all show as "unmanaged" in `netplan status` despite the MAC addresses matching up to those in the juju-created netplan.

Manually assigning IPs and routes restores functionality, but there is no indication of failure/error, just:
```
WARNING:root:Cannot call Open vSwitch: ovsdb-server.service is not running.
root@juju-3830cf-0-lxd-0:/etc/netplan# netplan status
     Online state: offline
    DNS Addresses: 127.0.0.53 (stub)
       DNS Search: .

● 1: lo ethernet UNKNOWN/UP (unmanaged)
      MAC Address: 00:00:00:00:00:00
        Addresses: 127.0.0.1/8
                   ::1/128

● 11: eth0 ethernet UP (unmanaged)
      MAC Address: 00:16:3e:bf:25:da
        Addresses: fe80::216:3eff:febf:25da/64 (link)
           Routes: fe80::/64 metric 256

● 13: eth1 ethernet UP (unmanaged)
      MAC Address: 00:16:3e:7a:c1:6e
        Addresses: fe80::216:3eff:fe7a:c16e/64 (link)
           Routes: fe80::/64 metric 256

```

[Boris Lukashev (rageltman)]

Current fix inside the LXD is `apt install netplan.io=0.104-0ubuntu2 libnetplan0=0.104-0ubuntu2 -y --allow-downgrades && reboot` which results in them coming up with working ifaces... netplan 105 is no longer in the repos and 106 breaks on configurations generated by older kit.

Juju, LXD, and NetPlan are great ideas but they require inter-version compatibility (at least forward-facing) to be viable.

[Boris Lukashev (rageltman)]

Not just LXDs but juju-provisioned machines too... hardware is coming up network-less.

[Danilo Egea Gondolfo (danilogondolfo)]

Hello, thanks for your bug report.

This seems to be a duplicate of https://bugs.launchpad.net/ubuntu/+source/netplan.io/+bug/2041480

The problem you are facing happened due to a change in behavior in netplan 0.106 where matching by MAC addresses was changed to only work with interfaces that have a permanent MAC address, which is not the case for virtual-ethernets used by LXD containers. This has always been the intended way the "match" keyword is used (only for physical devices). Upgrading Juju to 2.9.44+ should address this issue.

Removing the "match" key from your containers should also resolve the problem.

Please, check the bug report mentioned above for more details.

Although, it doesn't change anything for physical interfaces. You mentioned that your hardware lost its IPs as well. Can you provide more details on that?

Thank!