[Bug 1649931] Re: systemd-networkd needs to ensure DNS is up before network-online.target

Thu Dec 15 21:43:48 UTC 2016

On Thu, Dec 15, 2016 at 10:27 PM, Brian Murray <brian at ubuntu.com> wrote:

> How is this fixed in the development release?
>

There is an upstream resolvconf bug that addresses that package portion:

 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=847440

> Also the having a "Regression Potential" of low just because not a lot
> of people use the service is wrong.  A bad change could still horribly
> impact the users of the software, regardless of how many users there
> are.
>

I don't disagree (that saying few folks impacted means low).

This portion was split out from the previous systemd SRU

https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1636912

in which the changes were classified in the same way, so I was coping over
the assessment done by pitti and Foundations with which I agree.

I'd be happy if someone else could comment on whether they disagree with
the assessment.

IMO the risk is low:

The changes involve running resolvconf.service earlier (which sets an
inotify watch) and
does not regress anyone AFAICT.

Asking that DNS services (systemd-networkd-resolvconf-update.service) to
run before
network-online.target vs.  (how it is today) running after
network-online.target is reach
 also has low regression potential since _nothing_ requiring networking
should
run before systemd reaches network-online.target anyhow.

These potential users would already be broken since the units don't
currently
ensure that resolvconf (when  using networkd instead of
networking.service/ifupdown)
runs to completion before reaching network-online.target.

>
> ** Changed in: resolvconf (Ubuntu)
>        Status: New => Incomplete
>
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> https://bugs.launchpad.net/bugs/1649931
>
> Title:
>   systemd-networkd needs to ensure DNS is up before network-
>   online.target
>
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https://bugs.launchpad.net/bugs/1649931

Title:
  systemd-networkd needs to ensure DNS is up before network-
  online.target

Status in resolvconf package in Ubuntu:
  Incomplete
Status in systemd package in Ubuntu:
  New

Bug description:
  Currently resolvconf and systemd-networkd don't ensure DNS has been
  configured before allowing network-online.target to be reached.

  This was discussed in https://launchpad.net/bugs/1636912 however it
  was not a regression since there aren't any users of networkd + DNS
  early in boot at this time, it was requested that we move this DNS
  issue to a separate bug.

  [SRU]
  Fix: switch resolvconf.service to run Before=network-pre.target and add Wants=network-pre.target.  Add a Before=network-online.target to systemd-networkd-resolvconf-update.service to ensure we update /etc/resolv.conf with DNS config prior to reaching network-online.target.

  Regression potential: Low. networkd is not widely being used outside
  of netplan/snappy in xenial.

  Test Case:
    lxc launch ubuntu-daily:xenial x1
    lxc exec x1 /bin/bash

    # make sure you're on systemd-229-4ubuntu13
    apt update && apt install -y systemd

    # enable networkd and netplan
    apt install -y nplan
  cat <<EOF > /etc/netplan/nplan.yaml
  network:
    version: 2
    ethernets:
      eth0:
        dhcp4: true
  EOF
    sed -i.orig -e 's/^source/# source/' /etc/network/interfaces

    netplan generate

    # make sure cloud-init.service uses networkd
    sed -i.orig -e '/After=networking.service/a After=systemd-network-wait-online.service' /lib/systemd/system/cloud-init.service

    reboot

    # check that the order of execution with:
    journalctl -o short-precise --unit resolvconf.service --unit network-online.target --unit systemd-networkd-wait-online.service --unit systemd-networkd-resolvconf-update.service

    # the order should be:
      1. resolvconf:  systemd[1]: Started Nameserver information manager.
      2. systemd-networkd-wait-online.service:  systemd[1]: Starting Wait for Network to be Configured...
      3. systemd-networkd-resolvconf-update.service: systemd[1]: Started Update resolvconf for networkd DNS.
      4. network-online.target: systemd[1]: Reached target Network is Online.

  === BAD OUTPUT ===
  On a failing system, Reached target Network is Online occurs before (1, 2, or 3) above, like this output:

  Dec 15 19:18:15.233443 x4 systemd[1]: Started Nameserver information manager.
  Dec 15 19:18:15.797857 x4 systemd[1]: Starting Wait for Network to be Configured...
  Dec 15 19:18:15.799573 x4 systemd-networkd-wait-online[145]: ignoring: lo
  Dec 15 19:18:15.804949 x4 systemd-networkd-wait-online[145]: ignoring: lo
  Dec 15 19:18:15.805079 x4 systemd-networkd-wait-online[145]: ignoring: lo
  Dec 15 19:18:29.100305 x4 systemd[1]: Starting Update resolvconf for networkd DNS...
  Dec 15 19:18:29.101870 x4 systemd[1]: Started Wait for Network to be Configured.
  Dec 15 19:18:29.102144 x4 systemd[1]: Reached target Network is Online.
  Dec 15 19:18:29.212842 x4 systemd[1]: Started Update resolvconf for networkd DNS.

  === GOOD OUTPUT ===
  On a passing system, Reached target Network is Online occurs after 1, 2, and 3.

  Dec 15 19:28:42.548545 x4 systemd[1]: Started Nameserver information manager.
  Dec 15 19:28:43.144389 x4 systemd[1]: Starting Wait for Network to be Configured...
  Dec 15 19:28:43.146155 x4 systemd-networkd-wait-online[145]: ignoring: lo
  Dec 15 19:28:56.081487 x4 systemd[1]: Started Wait for Network to be Configured.
  Dec 15 19:28:56.100353 x4 systemd[1]: Starting Update resolvconf for networkd DNS...
  Dec 15 19:28:56.124005 x4 systemd[1]: Started Update resolvconf for networkd DNS.
  Dec 15 19:28:56.124555 x4 systemd[1]: Reached target Network is Online.

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