Public bug reported:
Upgrading the systemd package, which contains systemd-networkd, appears
to restart networkd and subsequently reconfigure network interfaces
causing a brief connectivity outage.
This is a bionic system which has a network bridge as it's primary
interface through netplan.
You can see from the logs that the interface appears to have been briefly taken
down
> Jul 24 09:40:32 optane kernel: [ 1935.046068] br0: port 1(eno1) entered
> disabled state
We also see logs of networkd restarting
> 248 Jul 24 09:40:32 optane systemd[1]: Stopping Network Service...
> 253 Jul 24 09:40:32 optane systemd[1]: Stopped Network Service.
> 254 Jul 24 09:40:32 optane systemd[1]: Starting Network Service...
Based on the ordering of the messages from Avahi, I also believe that
the IP address was first removed, then it was taken down, brought back
up, and the IP re-added. But I can not state that with 100% certainty.
However if you just set an interface down manually (ip link set br0
down), usually Avahi notes the interface is relevant before the address
was removed. We see the opposite here. It's possible the ordering is
just not entirely deterministic though.
Jul 24 09:40:32 optane avahi-daemon[1611]: Withdrawing address record for
10.48.134.22 on br0.
Jul 24 09:40:32 optane avahi-daemon[1611]: Interface br0.IPv4 no longer
relevant for mDNS.
The main reason I noticed this, is that the unofficial oracle-
java8-installer package upgraded at the same time - and it's wget to
download java failed due to "Network is unreachable" as it was upgraded
as the same time. To be clear, I'm not suggesting necessarily that this
specific package was affected is the bug, but it's the reason I noticed
the restart and it did cause an upgrade failure which I resumed with
"dpkg --configure -a". However there are many other implications of the
network interface being reconfigured.
Generally it's probably just not ideal to have networkd restart and
reconfigure the network interfaces - no matter the possible causes. But
from a quick thought about realistic implications
- it seems the bridge was not deleted/re-created which would be bad for
systems using libvirt/lxd/etc where the VMs may drop off the bridge. The
interface index didn't change so hopefully we're safe from this one
("Jul 24 09:40:32 optane systemd-networkd[17118]: br0: netdev exists,
using existing without changing its parameters")
- Another use case other than oracle-java8-installer that is highly
likely to be impacted is daemons configured to bind to a specific IP
address. By default, those binds will fail if the IP address doesn't
exist. It's possible these two restarts will race and those services
will fail to restart. An example where this could happen, is Apache2. It
would probably be hard to reproduce but logically likely to occur in
some small number of cases.
- we potentially do want networkd to ideally restart to upgrade the
code, but ideally it would "diff" the network interface config and not
tear things down. I am using a 'switchport' match in my netplan config,
I wonder if this is related?
** Affects: systemd (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1783272
Title:
upgrading systemd package restarts systemd-networkd and briefly takes
down network interfaces
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