netplan and post-up/pre-down scripts

[Mathieu Trudel-Lapierre]

On Tue, Jan 17, 2017 at 1:02 AM, Mike Pontillo <mike.pontillo at canonical.com>
wrote:

> On Mon, Jan 16, 2017 at 7:35 AM, Mark Shuttleworth <mark at ubuntu.com>
> wrote:
>
>> Would 'got-link' and 'lost-link' be good names for this?
>>
>
> I'm not certain a new event name is needed for this functionality; it
> seems to me that the current definition of 'up' isn't quite correct.[1]
> (But all this might be a moot point depending on what is supported in
> networkd, and how it behaves.)
>
> I understand there have been several attempts to address this in the past,
> such as the 'allow-hotplug' option, ifplugd, ifupdown-extra,
> NetworkManager, and now networkd. IMHO, no solution is complete unless it
> properly separates adminStatus from operStatus, and holds off on confirming
> "link up" until both are "up". For backward compatibility, a boolean flag
> (similar to "allow-hotplug") should indicate whether or not the system is
> allowed to continue booting if the interface is down.[2]
>

I agree booting should continue for any device that is down even if it's
configured and marked as fine to still be down. I think rather than trying
to skip a long delay that would happen in some other cases, we should
revisit whether it makes sense for it to take 5 minutes; or even make this
configurable. 5 minutes is a lot; 1 minute is acceptable in many
configurations, 30 seconds is ideal in some. All this only makes sense for
DHCP-configured interfaces where the link is up but no DHCP response has
been received. If the link is down, there is no point in ever waiting. This
may need fixed in networkd and NM to allow configuring the DHCP timeout.

I do not know that any of the different network management tools were
planned to address administrative status of an interface. It may even in
fact require kernel work (I haven't looked yet) to allow its state to be
set to administratively down.

Please file a bug about this. I'll review and look how we can specify this
in netplan, and how we can drive it in the various backends... But I expect
it will require work in both networkd and NetworkManager before it does
work correctly. Servers aren't typically used in such a way, and setting
that option seems like it might be quite intrusive (I mean, of course the
default wouldn't be for interfaces to be administratively down, but I can
see issues coming up from it. One of them is how to do it in the first
place, and another is that it would only happen once the renderer
(networkd/NM) is up and running, so potentially you've already
sent/received packets on the interfaces... ideally, that shouldn't happen,
but maybe I'm overthinking it).


>
> Another subtle detail is that if an interface is administratively down,
> there should be an option to cause the NIC to take its physical link down.
> That way, whatever is on the other side of the link doesn't assume its peer
> is active. (This is standard behavior on a router or a switch, but may be
> atypical for a server... so I think the default behavior should continue be
> "leave the physical link up".)
>

Of course. If something is administratively down, we must think of it in
terms of *powered down*. Otherwise it's simply not configured.

/ Matt
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