EphemeralIPv4Network: when device has requested existing network config, but link is down, network setup does not bring link up

[Chad Smith]

EphemeralIPv4Network exists in success too early on network devices with link down.

When run against a network interfaces which already has the requested ip configuration and routes but hapeens to be "link down", EphemeralIPv4Network.bringup_device exits immediately after determining that the device has the expected ip address.

EphemeralIPv4Network should instead ensure that all configured aspects of a network interface are properly setup before returning the context.

Steps to reproduce:

echo > ephemeral_test.py <<EOF
#!/usr/bin/python3
from cloudinit import log
from cloudinit.net.dhcp import EphemeralDHCPv4
from cloudinit.cmd.devel import addLogHandlerCLI

LOG = log.getLogger('ephemeraldhcp')
addLogHandlerCLI(LOG, log.DEBUG)
with EphemeralDHCPv4() as lease:
      print('LEASE: %s' % lease)
EOF
chmod 755 ephemeral_test.py

lxc launch ubuntu-daily:bionic b1
lxc file push ephemeral_test.py b1/

# lxc has already completed configured the device, so we expect to only see the following ip commands

# 'ip', '-family', 'inet', 'addr', 'add' ...
# 'ip', 'route', 'show', '0.0.0.0/0'
lxc exec b1 /ephemeral_test.py | grep Running

# bringing down the link, I'd want to see EphemeralIPv4Network performing a call to [ip link set eth0 up ]

lxc exec b1 ip link eth0 down

lxc exec b1 /ephemeral_test.py | grep Running

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3278