juju sends "network" top level key to user.network-config in lxd containers

Bug Description

== Short summary ==
In lxd containers launched by juju,
/var/lib/cloud/seed/nocloud-net/network-config has:
has:
network:
config: disabled

That is invalid content. Cloud-init assumes content in 'network-config'
is already namespaced to 'network'. The correct content would be:

config: disabled

== Easy recreate ==
$ lxc launch ubuntu-daily:bionic \
"--config=user.network-config={'network': {'config': {'disabled'}}}"

== Longer Info ==
When looking at bug 1651497, I see containers that run cloud-init
have errors in a container's cloud-init log
(http://paste.ubuntu.com/p/5mKXC8pMwH/) like:
AttributeError: 'NoneType' object has no attribute 'iter_interfaces'
and
Failed to rename devices: Failed to apply network config names. Found bad network config version: None

After some looking guessing I realized that juju must be attempting to
disable cloud-init's network configuration via sending the following
into the nocloud seed (/var/lib/cloud/seed/nocloud-net/network-config)
via 'user.network-config'.

cloud-init can clearly handle this better, but juju should not be
sending invalid configuration.

Related bugs:
* bug 1651497: iscsid.service fails to start in container, results in failed dist-upgrade later on
* bug 1906187: Version tag is not respected when put last

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: cloud-init 18.3-9-g2e62cb8a-0ubuntu1~18.04.2
ProcVersionSignature: Ubuntu 4.18.0-8.9-generic 4.18.7
Uname: Linux 4.18.0-8-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.4
Architecture: amd64
CloudName: NoCloud
Date: Tue Oct 16 14:33:12 2018
PackageArchitecture: all
ProcEnviron:
TERM=xterm-256color
PATH=(custom, no user)
LANG=C.UTF-8
SourcePackage: cloud-init
UpgradeStatus: No upgrade log present (probably fresh install)
cloud-init-log-warnings:
2018年10月16日 14:32:01,706 - stages.py[WARNING]: Failed to rename devices: Failed to apply network config names. Found bad network config version: None
2018年10月16日 14:32:01,707 - util.py[WARNING]: failed stage init-local
AttributeError: 'NoneType' object has no attribute 'version'
2018年10月16日 14:32:02,366 - stages.py[WARNING]: Failed to rename devices: Failed to apply network config names. Found bad network config version: None
user_data.txt:
#cloud-config
{}

I knew there were a couple of bugs touching on this issue, but I didn't turn this one up in a search yesterday.

I seem to have duplicated it with:
https://bugs.launchpad.net/juju/+bug/1804493

The fix has landed in 2.4 and will be forward-ported to the the develop (2.5) branch soon.

This bug is fixed with commit adbd950a to cloud-init on branch master.
To view that commit see the following URL:
https://git.launchpad.net/cloud-init/commit/?id=adbd950a

This bug is believed to be fixed in cloud-init in version 18.5. If this is still a problem for you, please make a comment and set the state back to New

Thank you.

This bug was fixed in the package cloud-init - 18.5-1-g5b065316-0ubuntu1

---------------
cloud-init (18.5-1-g5b065316-0ubuntu1) disco; urgency=medium

* New upstream snapshot.
- Update to pylint 2.2.2.
- Release 18.5 (LP: #1808380)
- tests: add Disco release [Joshua Powers]
- net: render 'metric' values in per-subnet routes (LP: #1805871)
- write_files: add support for appending to files. [James Baxter]
- config: On ubuntu select cloud archive mirrors for armel, armhf, arm64.
(LP: #1805854)
- dhclient-hook: cleanups, tests and fix a bug on 'down' event.
- NoCloud: Allow top level 'network' key in network-config. (LP: #1798117)
- ovf: Fix ovf network config generation gateway/routes (LP: #1806103)

-- Ryan Harper <email address hidden> 2018年12月14日 14:45:46 -0600

The change made here seems to be having fallout at https://bugs.launchpad.net/ubuntu/+source/netplan.io/+bug/1906187

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3251