MAAS bridge script should drop all 'source' stanzas from original file

[Andrew McDermott]

We keep running into:

 https://bugs.launchpad.net/ubuntu/+source/cloud-init/+bug/1563296
 https://bugs.launchpad.net/curtin/+bug/1586075
 https://bugs.launchpad.net/maas/+bug/1588706
 https://bugs.launchpad.net/curtin/+bug/1582410

and it affects customers too:

 https://bugs.launchpad.net/juju-core/+bug/1603473

There is the advertised curtin workaround to remove both eth0.cfg and 50-cloud-init.cfg as the MAAS image is being deployed through a custom preseed - and this has worked and been sufficient to date.

However, the fixes in curtin have not moved from 'fix committed' and as such we continue to experience this issue. I propose that we change the bridge script to drop all 'source' stanzas so that we don't run into this problem anymore.

We had initially decided to use the workaround and leave the 'source' stanzas in place as that is the extension mechanism. I don't think we should we wait any longer as this is still hitting deployments of precise, trusty and xenial.

From a charmers perspective they can always add back the 'source' stanza if they find it missing during charm deployment. Our removal of the source stanza is a one-time affair.

From juju's perspective we should own the initial network configuration of the machine during the initial boot. If we drop the source stanzas our bridge procedure becomes:

  $ ifdown -a
  $ <rewrite-etc-network-interfaces-to-be-bridged>
  $ ifup -a

In this scenario we would take down all interfaces, including those originally source'd from /etc/network/interfaces.d/*.cfg and only bring up those interfaces in the newly created ENI which would no longer have the source stanza.

[Andrew McDermott (frobware)]

There are workarounds listed for this bug here:

  https://bugs.launchpad.net/maas/+bug/1590689

[Mick Gregg (macgreagoir)]

This may need to happen outside the bridge script, as containers can also need the eth0.cfg removed (and interfaces down/up-ed).

[Andrew McDermott (frobware)]

@mick - covered by https://bugs.launchpad.net/juju-core/+bug/1566801

[Anastasia (anastasia-macmood)]

Based on bug in comment 3 being `Fix Released`, I am marking this as `Fix Committed`.

[Andrew McDermott (frobware)]

This issues is still outstanding. Comment #3 & #4 was meant to convey that there was a separate fix for containers.

[Andrew McDermott (frobware)]

So despite my initial protestations we don't appear to run into this bug anymore - the set of things that we wanted in the distros is now up to date. I propose we close this bug.