[Bug 1902960] Re: Upgrade from 245.4-4ubuntu3.3 to 245.4-4ubuntu3.2 appears to break DNS resolution in some cases

[Dan Streetman]

As I mentioned in the upstream systemd bug, it's still not clear what
exactly is causing this, and the inability to reproduce it after the
image first boot, or with another image with debug added, or with the
latest image, means it will be impossible to verify any fix to this
problem.

However, my best guess is udevd is somehow missing the 'add' uevent for
the network device, as I described in the upstream bug. While I don't
know why it would miss the event, the upstream commit
e0e789c1e97e2cdf1cafe0c6b7d7e43fa054f151 should fix the problem, as it
will setup the proper udevd device parameters not only for 'add' but
also 'change' uevents.

So, based on those assumptions/guesses and on the relative safety of the
upstream commit, I plan to SRU that commit for this bug.

** Bug watch added: github.com/systemd/systemd/issues #17532
   https://github.com/systemd/systemd/issues/17532

** Also affects: systemd via
   https://github.com/systemd/systemd/issues/17532
   Importance: Unknown
       Status: Unknown

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Title:
  Upgrade from 245.4-4ubuntu3.3 to 245.4-4ubuntu3.2 appears to break DNS
  resolution in some cases

Status in cloud-images:
  New
Status in systemd:
  Unknown
Status in cloud-init package in Ubuntu:
  Confirmed
Status in systemd package in Ubuntu:
  Incomplete

Bug description:
  The systemd upgrade 245.4-4ubuntu3.3 to 245.4-4ubuntu3.2 appears to
  have broken DNS resolution across much of our Azure fleet earlier
  today.  We ended up mitigating this by forcing reboots on the
  associated instances, no combination of networkctl reload,
  reconfigure, systemctl daemon-reexec, systemctl daemon-reload, netplan
  generate, netplan apply would get resolvectl to have a DNS server
  again.  The main symptom appears to have been systemd-networkd
  believing it wasn't managing the eth0 interfaces:

  ubuntu at machine-1:~$ sudo networkctl
  IDX LINK TYPE     OPERATIONAL SETUP
    1 lo   loopback carrier     unmanaged
    2 eth0 ether    routable    unmanaged
                                                                            2 links listed.

  Which eventually made them lose their DNS resolvers:

  ubuntu at machine-1:~$ sudo resolvectl dns
  Global:
  Link 2 (eth0):

  After rebooting, we see this behaving properly:

  ubuntu at machine-1:~$ sudo networkctl list
  IDX LINK TYPE     OPERATIONAL SETUP
    1 lo   loopback carrier     unmanaged
    2 eth0 ether    routable    configured

  2 links listed.
  ubuntu at machine-1:~$ sudo resolvectl dns
  Global:
  Link 2 (eth0): 168.63.129.16

  This appears to be specifically linked to the upgrade, i.e. we were able to provoke the issue by upgrading the systemd package, so I suspect it's part of the packaging in the upgrade process.
  ---
  ProblemType: Bug
  ApportVersion: 2.20.11-0ubuntu27.10
  Architecture: amd64
  CasperMD5CheckResult: skip
  DistroRelease: Ubuntu 20.04
  Lspci-vt:
   -[0000:00]-+-00.0  Intel Corporation 440BX/ZX/DX - 82443BX/ZX/DX Host bridge (AGP disabled)
              +-07.0  Intel Corporation 82371AB/EB/MB PIIX4 ISA
              +-07.1  Intel Corporation 82371AB/EB/MB PIIX4 IDE
              +-07.3  Intel Corporation 82371AB/EB/MB PIIX4 ACPI
              \-08.0  Microsoft Corporation Hyper-V virtual VGA
  Lsusb: Error: command ['lsusb'] failed with exit code 1:
  Lsusb-t:

  Lsusb-v: Error: command ['lsusb', '-v'] failed with exit code 1:
  MachineType: Microsoft Corporation Virtual Machine
  Package: systemd 245.4-4ubuntu3.3
  PackageArchitecture: amd64
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   LANG=C.UTF-8
   SHELL=/bin/bash
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-1031-azure root=PARTUUID=2e08bba3-68b4-4a16-af3b-47b73bd138a9 ro console=tty1 console=ttyS0 earlyprintk=ttyS0 panic=-1
  ProcVersionSignature: Ubuntu 5.4.0-1031.32-azure 5.4.65
  Tags:  focal uec-images
  Uname: Linux 5.4.0-1031-azure x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: N/A
  _MarkForUpload: True
  dmi.bios.date: 12/07/2018
  dmi.bios.vendor: American Megatrends Inc.
  dmi.bios.version: 090008
  dmi.board.name: Virtual Machine
  dmi.board.vendor: Microsoft Corporation
  dmi.board.version: 7.0
  dmi.chassis.asset.tag: 7783-7084-3265-9085-8269-3286-77
  dmi.chassis.type: 3
  dmi.chassis.vendor: Microsoft Corporation
  dmi.chassis.version: 7.0
  dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr090008:bd12/07/2018:svnMicrosoftCorporation:pnVirtualMachine:pvr7.0:rvnMicrosoftCorporation:rnVirtualMachine:rvr7.0:cvnMicrosoftCorporation:ct3:cvr7.0:
  dmi.product.name: Virtual Machine
  dmi.product.uuid: 4412ad79-83fa-f845-b7c2-6f30dd4f1950
  dmi.product.version: 7.0
  dmi.sys.vendor: Microsoft Corporation

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