[Bug 1770082] Re: systemd-networkd not renaming devices on boot

[Ryan Harper]

"This is why I added
cloud-init to affected packages -- cloud-init should not be second-
guessing the network layer and attempting to do renames / to run"

There is no second guessing.  In the case where we have no network
config, there is no renaming; we accept whatever name is given.

If the config passed to cloud-init includes a name for an interface, then
cloud-init applies that name; this is the MAAS scenario;

Given the unreliable nature of udev w.r.t naming (see this very bug)
The *only* way for cloud-init to ensure that a directive to name an interface
matches the config (also note cloud-init accepts network config in
various formats
not just netplan) is to handle naming if requested directly, precisely
due to this bug.

If we fix systemd-udevd to allow renames of interfaces reliably that helps
most cases where udevd runs.  For the remaining cases where udev doesn't run,
containers for example, cloud-init will still need to use iproute2 to
set an interface
name if requested.


On Fri, May 25, 2018 at 8:55 AM, Mathieu Trudel-Lapierre
<mathieu.tl at gmail.com> wrote:
> netplan changes are available in git:
>
> Daniel's patch to write udev rules (SRU material):
> https://github.com/CanonicalLtd/netplan/commit/b0c51bfa8ba8b898a9feaed9cd7d8790d147d35d
>
> Daniel's patch + dropping replug code + rework 'netplan apply' (code for cosmic); in progress for upload to cosmic:
> https://github.com/CanonicalLtd/netplan/tree/live-rename
>
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> Title:
>   systemd-networkd not renaming devices on boot
>
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https://bugs.launchpad.net/bugs/1770082

Title:
  systemd-networkd not renaming devices on boot

Status in netplan:
  Confirmed
Status in cloud-init package in Ubuntu:
  Confirmed
Status in systemd package in Ubuntu:
  Confirmed

Bug description:
  === systemd issue ===

  Renaming devices doesn't seem to work.

  If I disable all other network configuration and create
  /etc/systemd/network/10-network.link with:

  [Match]
  MACAddress=52:54:00:c1:c9:bb

  [Link]
  Name=myiface3

  I expect this to cause the device with that MAC address to be renamed
  to  myiface3. However, when I reboot, I instead see:

  $ ip l
  1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
      link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
  2: ens3: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
      link/ether 52:54:00:c1:c9:bb brd ff:ff:ff:ff:ff:ff

  The device is not renamed.

  This link file is pretty much identical to Example 2 in
  https://www.freedesktop.org/software/systemd/man/systemd.link.html.

  The renaming does work if I boot with net.ifnames=0, and oddly, it
  also works if I unbind the device and rebind it as netplan apply does.
  No setting of NamePolicy seems to help.

  === Original Bug ==

  'set-name:' doesn't change the name of a network interface on boot, it
  only works when you do netplan apply.

  Say I take this 50-cloud-init.yaml file:

  # This file is generated from information provided by
  # the datasource.  Changes to it will not persist across an instance.
  # To disable cloud-init's network configuration capabilities, write a file
  # /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
  # network: {config: disabled}
  network:
      version: 2
      ethernets:
          ens3:
              dhcp4: true
              match:
                  macaddress: 52:54:00:de:bd:f6
              set-name: ens3

  Say I change set-name to 'myiface3' and reboot. I expect that the
  device will be called myiface3 and brought up fine with dhcp. However,
  instead I see:

  $ ip a
  1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
      link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
      inet 127.0.0.1/8 scope host lo
         valid_lft forever preferred_lft forever
      inet6 ::1/128 scope host
         valid_lft forever preferred_lft forever
  2: ens3: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
      link/ether 52:54:00:de:bd:f6 brd ff:ff:ff:ff:ff:ff

  The name has not been changed, and the device has not been brought up.

  If I run netplan apply however, I see the following:

  1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
      link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
      inet 127.0.0.1/8 scope host lo
         valid_lft forever preferred_lft forever
      inet6 ::1/128 scope host
         valid_lft forever preferred_lft forever
  3: myiface3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
      link/ether 52:54:00:de:bd:f6 brd ff:ff:ff:ff:ff:ff
      inet 192.168.122.151/24 brd 192.168.122.255 scope global dynamic myiface3
         valid_lft 3575sec preferred_lft 3575sec
      inet6 fe80::5054:ff:fede:bdf6/64 scope link
         valid_lft forever preferred_lft forever

  So names are successfully changed with netplan apply.

  This seems to be some udev-related timing or priority issue that I'm
  still trying to hunt down.

  This breaks some forms of migration in certain cloud environments.

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