[Bug 1997124] Re: Netplan/Systemd/Cloud-init/Dbus Race

[Rod Smith]

We've run into this in the Server Certification lab on mouser, a NEC
Express5800/R128h-1M server. In our testing, it's affected 50% (2 of 4)
Ubuntu 20.04 deployments, but not 18.04 or 22.04 deployments (0 of 3 for
each of those). These sample sizes are low, so this may be a
coincidence; but I'm mentioning it here in case it's not a coincidence.

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Title:
  Netplan/Systemd/Cloud-init/Dbus Race

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

Bug description:
  Cloud-init is seeing intermittent failures while running `netplan
  apply`, which appears to be caused by a missing resource at the time
  of call.

  The symptom in cloud-init logs looks like:

  Running ['netplan', 'apply'] resulted in stderr output: Failed to
  connect system bus: No such file or directory

  I think that this error[1] is likely caused by cloud-init running
  netplan apply too early in boot process (before dbus is active).

  Today I stumbled upon this error which was hit in MAAS[2]. We have
  also hit it intermittently during tests (we didn't have a reproducer).

  Realizing that this may not be a cloud-init error, but possibly a
  dependency bug between dbus/systemd we decided to file this bug for
  broader visibility to other projects.

  I will follow up this initial report with some comments from our
  discussion earlier.

  [1] https://github.com/canonical/netplan/blob/main/src/dbus.c#L801
  [2] https://discourse.maas.io/t/latest-ubuntu-20-04-image-causing-netplan-error/5970

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