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[Scott Moser <smoser@xxxxxxxxxx>]

** Also affects: resolvconf (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1675571

Title:
  Cloud-init update renders secondary addresses ti be incompatible with
  standard tools

Status in cloud-init:
  Confirmed
Status in cloud-init package in Ubuntu:
  Confirmed
Status in resolvconf package in Ubuntu:
  New

Bug description:
  The change of how cloud-init renders /etc/network/interface.d/50-cloud-init.cfg, standard tools no longer work as expected:
  * resolvconf will nullify nameservers
  * if* commands ignore secondary addresses

  The rendering is considered dangerous per Debian (https://wiki.debian.org/NetworkConfiguration), to whit:
  "Also, ifupdown supports specifying multiple interfaces by repeating iface sections with the same interface name. The key difference from the method described above is that all such sections are treated by ifupdown as just one interface, so user can't add or remove them individually. However, up/down commands, as well as scripts, are called for every section as it used to be.

  "Note however that this method is dangerous! Certain driver/hardware combinations may sometimes fail to bring the link up if no labels are assigned to the alias interfaces. (Seen this on Debian Wheezy and Jessie with RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 01) auto-negotiating to 10/full. A similar warning from another person exists in the history of this page.)
  "

  
  [ORIGINAL REPORT]

  Regresion from Bug #1657940.

  When provisioning with multiple eth0 addresses, /etc/resolv.conf is
  empty:

  Consider:
  root@tester:~# 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

  auto eth0
  iface eth0 inet static
      address 138.197.98.102
      dns-nameservers 8.8.8.8 8.8.4.4
      gateway 138.197.96.1
      netmask 255.255.240.0

  # control-alias eth0
  iface eth0 inet static
      address 10.17.0.11
      netmask 255.255.0.0

  Which then yields an empty /etc/resolv.conf:
  root@tester:/run/resolvconf# cat interface/eth0.inet

  root@tester:/run/resolvconf# 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

  The problem is that resolvconfg does pattern matching for eth*.inet.
  The second definition of eth0 has no nameserver and therefore
  overrides the definition.

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