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

[Steve Langasek]

On Thu, Dec 15, 2016 at 09:43:48PM -0000, Ryan Harper wrote:
> 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 point here is that 'regression potential' is not meant to be a scalar,
it's meant to be a description of where regressions are possible so that we
can assess whether additional testing is needed to guard against those
regressions.

And also to ensure that the SRU submitter has carefully thought about this
question, since going through that exercise usually results in a better SRU.

-- 
You received this bug notification because you are a member of Ubuntu
Sponsors Team, which is subscribed to the bug report.
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:
  Fix Released
Status in systemd package in Ubuntu:
  New
Status in resolvconf source package in Xenial:
  New
Status in systemd source package in Xenial:
  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.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/resolvconf/+bug/1649931/+subscriptions