[Bug 1750884] Re: [2.4, bionic] /etc/resolv.conf not configured correctly in Bionic, leads to no DNS resolution

[Dimitri John Ledkov]

If we don't know, then maybe things should be passed to netplan, in a way for it to generate global resolved config? as in, create
/run/systemd/resolved.conf.d/global.conf

[Resolve]
DNS=999.999.999.999
(Maybe FallbackDNS=, if we want it to leave DNS= setting for users to tweak)

Or whatnot, which should then appear in systemd-resolve --status, Global
section which is applied as a fallback if an interface does not have a
per-interface DNS settings.

Could somebody try dropping dns configs out of netplan file that is
generated, rerun apply, check that systemd-resolve --status  has
nothing, then add above drop-in with the right dns server, restart
resolved, and check if that picks up a global DNS server, and if network
resolution works correctly? *globally*

I also wonder, if .network / .link files should have an ability to
specify Global DNS settings for resolved...

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Title:
  [2.4, bionic] /etc/resolv.conf not configured correctly in Bionic,
  leads to no DNS resolution

Status in cloud-init:
  New
Status in MAAS:
  Triaged
Status in nplan package in Ubuntu:
  New
Status in systemd package in Ubuntu:
  New

Bug description:
  When deploying Bionic, /etc/resolv.conf is not configured correctly,
  which leads to no DNS resolution. In the output below, you will see
  that netplan config is correctly to the 10.90.90.1 nameserver, but in
  resolv.conf that's a local address.

  Resolv.conf should really be configured to use the provided DNS
  server(s). That said, despite that fact, DNS resolution doesn't work
  with the local address.

  Bionic
  ------

  ubuntu at node01:~$ cat /etc/netplan/50-cloud-init.yaml
  # This file is generated from information provided by
  # the datasource.  Changes to it will not persist across an instance.
  # To disable cloud-init's network configuration capabilities, write a file
  # /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
  # network: {config: disabled}
  network:
      version: 2
      ethernets:
          enp0s25:
              match:
                  macaddress: b8:ae:ed:7d:17:d2
              mtu: 1500
              nameservers:
                  addresses:
                  - 10.90.90.1
                  search:
                  - maaslab
                  - maas
              set-name: enp0s25
      bridges:
          br0:
              addresses:
              - 10.90.90.3/24
              gateway4: 10.90.90.1
              interfaces:
              - enp0s25
              parameters:
                  forward-delay: 15
                  stp: false
  ubuntu at node01:~$ cat /etc/resolv.conf
  # This file is managed by man:systemd-resolved(8). Do not edit.
  #
  # 127.0.0.53 is the systemd-resolved stub resolver.
  # run "systemd-resolve --status" to see details about the actual nameservers.
  nameserver 127.0.0.53

  search maaslab maas
  ubuntu at node01:~$ ping google.com
  ping: google.com: Temporary failure in name resolution

  [...]

  ubuntu at node01:~$ sudo vim /etc/resolv.conf
  ubuntu at node01:~$ cat /etc/resolv.conf
  # This file is managed by man:systemd-resolved(8). Do not edit.
  #
  # 127.0.0.53 is the systemd-resolved stub resolver.
  # run "systemd-resolve --status" to see details about the actual nameservers.
  nameserver 10.90.90.1

  search maaslab maas
  ubuntu at node01:~$ ping google.com
  PING google.com (172.217.0.174) 56(84) bytes of data.
  64 bytes from mia09s16-in-f14.1e100.net (172.217.0.174): icmp_seq=1 ttl=52 time=4.46 ms
  64 bytes from mia09s16-in-f14.1e100.net (172.217.0.174): icmp_seq=2 ttl=52 time=4.38 ms

  =============================
  Xenial
  ==============================

  ubuntu at node05:~$ cat /etc/network/interfaces.d/50-cloud-init.cfg
  # This file is generated from information provided by
  # the datasource.  Changes to it will not persist across an instance.
  # To disable cloud-init's network configuration capabilities, write a file
  # /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
  # network: {config: disabled}
  auto lo
  iface lo inet loopback
      dns-nameservers 10.90.90.1
      dns-search maaslab maas

  auto enp0s25
  iface enp0s25 inet static
      address 10.90.90.162/24
      gateway 10.90.90.1
      mtu 1500
  ubuntu at node05:~$ cat /etc/resolv.conf
  # Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
  #     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
  nameserver 10.90.90.1
  search maaslab maas

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