Running "netplan apply" to add a new interface removed the IPs of several other interfaces

[Barry Price]

We have a split network setup on one host, with per-role netplan configs, e.g.

/etc/netplan/01-provider.yaml
/etc/netplan/02-dmz.yaml
/etc/netplan/03-lan.yaml
/etc/netplan/04-manlan.yaml
/etc/netplan/05-etc.yaml

A single new network+vlan (a private /24 with the .1 IP set to come up on this host) was added to what we'll call /etc/netplan/05-etc.yaml, and "netplan apply" was run - we saw no output.

That new interface on the new net/vlan came up fine, so we called the job done.

We later realised that we'd lost the IPs of several unrelated interfaces not even defined in that yaml files, so completely unrelated to the recent change. The interfaces remained defined, but with no IP.

Re-running 'netplan apply' restored those IPs.

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 20.04.6 LTS
Release: 20.04
Codename: focal
$ dpkg -l netplan.io
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-==============-======================-============-===========================================================
ii netplan.io 0.104-0ubuntu2~20.04.2 amd64 YAML network configuration abstraction for various backends
$