[Bug 1734167] Re: DNS doesn't work in no-cloud as launched by ubuntu

[Ryan Harper]

I suspect because in bionic/artful we're missing resolvconf package, that the systemd-resolved service ends up starting later in boot.  The systemd-resolved-update-resolveconf.{service,path} require /sbin/resolvconf to run;  this service had a path-based trigger that would get hooked whenever DHCP clients would call resolvconf to kick off a DNS update once config was available.
I suspect that systemd-networkd itself isn't poking DNS service properly after acquiring information.

The dependency loop comes from systemd-resolved using default
dependencies which run after when cloud-init.service would run.

This then needs systemd-resolved to specify DefaultDependencies=No and
something like network-online.target to require systemd-resolved.

I modified cloud-init.service to include an After=systemd-
resolved.service but some other service may require dns, so I feel this
is a property of network-online.target.

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https://bugs.launchpad.net/bugs/1734167

Title:
  DNS doesn't work in no-cloud as launched by ubuntu

Status in cloud-init:
  Confirmed
Status in cloud-init package in Ubuntu:
  Confirmed
Status in systemd package in Ubuntu:
  Confirmed
Status in cloud-init source package in Zesty:
  Fix Released
Status in systemd source package in Zesty:
  Fix Released
Status in cloud-init source package in Artful:
  Confirmed
Status in systemd source package in Artful:
  Confirmed
Status in cloud-init source package in Bionic:
  Confirmed
Status in systemd source package in Bionic:
  Confirmed

Bug description:
  I use no-cloud to test the kernel in CI (I am maintainer of the bcache
  subsystem), and have been running it successfully under 16.04 cloud
  images from qemu, using a qemu command that includes:

  -smbios "type=1,serial=ds=nocloud-
  net;s=https://raw.githubusercontent.com/mlyle/mlyle/master/cloud-
  metadata/linuxtst/"

  As documented here:

  http://cloudinit.readthedocs.io/en/latest/topics/datasources/nocloud.html

  Under the new 17.10 cloud images, this doesn't work: the network comes
  up, but name resolution doesn't work-- /etc/resolv.conf is a symlink
  to a nonexistent file at this point of the boot and systemd-resolved
  is not running.  When I manually hack /etc/resolv.conf in the cloud
  image to point to 4.2.2.1 it works fine.

  I don't know if nameservice not working is by design, but it seems
  like it should work.  The documentation states:

  "With ds=nocloud-net, the seedfrom value must start with http://,
  https:// or ftp://"

  And https is not going to work for a raw IP address.

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