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[Mathew Hodson <mathew.hodson@xxxxxxxxx>]

snapd was updated in bug 1640978

** No longer affects: snapd (Ubuntu)

** No longer affects: snapd (Ubuntu Xenial)

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https://bugs.launchpad.net/bugs/1621336

Title:
  snapd.boot-ok.service hangs eternally on cloud image upgrades

Status in cloud-init package in Ubuntu:
  Fix Released
Status in cloud-init source package in Xenial:
  Fix Released

Bug description:
  ==== Begin SRU Template [cloud-init] ====
  [Impact] 
  One of cloud-init's features is to upgrade the system during first boot so that it is fully up to date when the user code starts running.

  [Test Case]
  launch an old instance of 16.04 that will need an update to snapd with
  user-data that indicates a package upgrade should be done.

  $ lxc image show ubuntu:74a491804877
  autoupdate: false
  properties:
    aliases: 16.04,default,lts,x,xenial
    architecture: amd64
    description: ubuntu 16.04 LTS amd64 (release) (20160830)
    label: release
    os: ubuntu
    release: xenial
    serial: "20160830"
    version: "16.04"
  public: true

  $ printf "#%s\n%s\n" cloud-config "packages: [snapd]" > user-data

  $ lxc launch ubuntu:74a491804877 xrecreate "--config=user.user-data=$(cat user-data)"
  $ lxc exec xrecreate -- tail -f /var/log/cloud-init-output.log

  # you will see the output log hang at:
  # Setting up snapd (2.14.2~16.04) ...

  
  ## Now get new container and patch in cloud-init
  $ lxc launch ubuntu:74a491804877 xpatched
  # let it boot, with no user-data saying to update.
  $ sleep 10

  # update the container to new cloud-init, then clean it to make
  # it look like first boot again.
  $ lxc file push - xpatched/etc/cloud/cloud.cfg.d/update.cfg < user-data
  $ lxc exec xpatched -- sh -c '
      p=/etc/apt/sources.list.d/proposed.list
      echo deb http://archive.ubuntu.com/ubuntu xenial-proposed main > "$p" &&
      apt-get update -q && apt-get -qy install cloud-init'
  $ lxc exec xpatched -- sh -c '
      cd /var/lib/cloud && for d in *; do [ "$d" = "seed" ] || rm -Rf "$d"; done
      rm -Rf /var/log/cloud-init*'

  $ lxc exec xpatched reboot
  $ lxc exec xpatched -- tail -f /var/log/cloud-init-output.log

  # snapd installed and a 'Cloud-init finished' message.

  [Regression Potential] 
  The change to running package installation later in boot will likely affect some things.  However, previously a larger set of things were unreliable.  This will make things over all more reliable.
  ==== End SRU Template [cloud-init] ====

  I reproducibly run into an eternal hang when deploying services with
  Juju, when it prepares a new xenial testbed. The current xenial cloud
  image does not have the latest snapd, so snapd gets dist-upgraded:

  Preparing to unpack .../snapd_2.14.2~16.04_amd64.deb ...
  Warning: Stopping snapd.service, but it can still be activated by:
    snapd.socket
  Unpacking snapd (2.14.2~16.04) over (2.13) ...
  Setting up snapd (2.14.2~16.04) ...
  [...] hangs

  The postinst tries to start snapd.boot-ok.service on upgrade:

             |-cloud-init(311)-+-apt-get(577)---dpkg(845)---snapd.postinst(846)---perl(919)---systemctl(922)
             |                 `-sh(354)---tee(355)

  root       922  0.0  0.0  25316  1412 pts/0    S+   06:09   0:00
  /bin/systemctl start snapd.boot-ok.service

  This hangs eternally because:

   - cloud-init's dist-upgrade runs *during* the boot process, so that
  the system is not fully booted yet when this happens (see bug
  1576692); thus multi-user.target is *not* yet active

   - snapd.boot-ok.service is After=multi-user.target

   - "systemctl start" is synchronous by default, i. e. it waits until
  the service is started unless you use --no-block.

  Thus snapd.postinst waits on snapd.boot-ok.service waits on multi-
  user.target waits on cloud-init to finish waits on snapd.postinst to
  finish.

  I think conceptually you shouldn't start snapd.boot-ok.service in the
  postinst; if the system is already booted (manual dist-upgrade) it
  should already be running, and if it does get upgraded during boot
  (with cloud-init) then you shouldn't pretend that booting is already
  finished. So I suggest to use dh_installinit with --no-scripts for
  snapd.boot-ok.service.

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