[Bug 1806777] Re: cloud-init with iscsi ibft keeps interface at 'manual' so the system gets no dns search domain

[Dan Streetman]

Discussed with @smoser and we think this can be fixed in open-iscsi's
initramfs local-top script; I am patching and testing now.

** Also affects: open-iscsi (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: open-iscsi (Ubuntu Xenial)
       Status: New => In Progress

** Changed in: open-iscsi (Ubuntu Xenial)
     Assignee: (unassigned) => Dan Streetman (ddstreet)

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Title:
  cloud-init with iscsi ibft keeps interface at 'manual' so the system
  gets no dns search domain

Status in cloud-init:
  Invalid
Status in cloud-init package in Ubuntu:
  Invalid
Status in open-iscsi package in Ubuntu:
  New
Status in cloud-init source package in Trusty:
  Invalid
Status in open-iscsi source package in Trusty:
  New
Status in cloud-init source package in Xenial:
  In Progress
Status in open-iscsi source package in Xenial:
  In Progress
Status in cloud-init source package in Bionic:
  Invalid
Status in open-iscsi source package in Bionic:
  New

Bug description:
  [impact]

  in bug 1752391, cloud-init was updated to check if the initramfs has
  specific iscsi root device config (e.g. static initramfs config, or
  ibft), and if so then set up the interface in e/n/i but do not mark it
  as 'auto'.  This prevents ifupdown from actually running dhclient for
  the interface; the reason for the change in that bug was to prevent a
  hang at shutdown, as taking down the interface removes access to the
  iscsi root disk (thus hanging the system).

  However, iBFT has no mechanism in its spec to provide the DNS search
  domain, so while the interface ip address/netmask and gateway is
  correctly set up when the system finishes booting, it does not contain
  any search domain in /etc/resolv.conf.  There is no way to get this
  information except from an actual dhcp query/response.

  In the initramfs, if open-iscsi does not detect ibft (or have static
  config built-in) then it will not create a /run/net-IFACE.conf file;
  if it does find ibft (or have static config) it will create a /run
  /net-IFACE.conf file with the config data that it has (e.g. with ibft,
  all the interface configuration that ibft is able and configured to
  provide).  After this (setting up the interface and mounting the root
  dev), ipconfig runs and checks for the existence of /run/net-
  IFACE.conf file.  If it does NOT exist, then ipconfig creates it
  containing the result of the dhcp lease response that ipconfig
  received - which includes the dns search domain.  However, if there is
  already a /run/net-IFACE.conf file, ipconfig does NOT update it.  So,
  the file created by open-iscsi remains, without any dns search domain.

  Once the system boots, resolvconf checks for existance of the /etc
  /net-IFACE.conf file, and if found it transfers some of the data into
  /etc/resolv.conf (e.g. the dns search domain).  Since it does not
  contain any dns search domain, the /etc/resolv.conf file does not
  contain it either.

  If the system is configured to start dhclient for the interface, then
  dhclient receives and sets up the system resolv.conf to use the dns
  search domain correctly.

  For trusty: cloud-init is very different and sets up the running
  system ifupdown to start dhclient for the root device interface.  The
  dns search domain is therefore configured by dhclient in the runtime
  system.

  For xenial: cloud-init sets up the iscsi root device's interface with
  a e/n/i configuration for dhcp, but leaves its 'auto' line commented
  out, e.g.:

  # control-manual ens3f0
  iface ens3f0 inet dhcp
      dns-nameservers 169.254.169.254
      gateway 10.0.0.1

  this results in no dns search domain for the system.

  For bionic and later: cloud-init sets up netplan instead of ifupdown;
  netplan has no such 'auto' mechanism, but it creates systemd-networkd
  .network file with the "CriticalConnection" parameter set to true,
  which prevents systemd-networkd from ever taking the interface down,
  which avoids the hang on shutdown (or any other time dhcp fails/stops
  for the interface).

  [test case]

  start a xenial system that uses ibft and check /etc/resolv.conf; there
  will be no dns search domain.

  [regression potential]

  depending on the specific fix, this has the potential to cause the
  interface to be taken down which would then hang the system (due to
  root device being iscsi).

  [other info]

  this appears to have been introduced by bug 1752391.  This bug may
  possibly also exist if the "ip=" parameter is used, which also
  triggers the cloud-init code that sets the runtime interface to
  'manual' instead of 'auto', though I have not specifically tested
  that.

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