Public bug reported:
[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.
** Affects: cloud-init
Importance: Undecided
Status: Invalid
** Affects: cloud-init (Ubuntu)
Importance: Undecided
Status: Invalid
** Affects: cloud-init (Ubuntu Trusty)
Importance: Undecided
Status: Invalid
** Affects: cloud-init (Ubuntu Xenial)
Importance: Medium
Assignee: Dan Streetman (ddstreet)
Status: In Progress
** Affects: cloud-init (Ubuntu Bionic)
Importance: Undecided
Status: Invalid
** Also affects: cloud-init (Ubuntu)
Importance: Undecided
Status: New
** Changed in: cloud-init
Status: New => Invalid
** Also affects: cloud-init (Ubuntu Bionic)
Importance: Undecided
Status: New
** Also affects: cloud-init (Ubuntu Xenial)
Importance: Undecided
Status: New
** Also affects: cloud-init (Ubuntu Trusty)
Importance: Undecided
Status: New
** Changed in: cloud-init (Ubuntu Trusty)
Status: New => Invalid
** Changed in: cloud-init (Ubuntu Bionic)
Status: New => Invalid
** Changed in: cloud-init (Ubuntu Xenial)
Status: New => In Progress
** Changed in: cloud-init (Ubuntu Xenial)
Assignee: (unassigned) => Dan Streetman (ddstreet)
** Changed in: cloud-init (Ubuntu)
Status: New => Invalid
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https://bugs.launchpad.net/bugs/1806777
Title:
cloud-init with iscsi ibft keeps interface at 'manual' so the system
gets no dns search domain
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