cloud-init

cloud-init should configure networkmanager to not manage /etc/resolv.conf

Bug #1693251 reported by Lars Kellogg-Stedman on 2017-05-24

This bug affects 1 person

Affects		Status	Importance	Assigned to	Milestone
	cloud-init	Fix Released	Medium	Ryan McCabe

Bug Description

Currently, cloud-init adds nameserver entries directly to /etc/resolv.conf but does not configure namservers in per-interface configuration files. This could be problematic because information received from other sources (e.g., from another interface that is using dhcp) could clobber the information in /etc/resolv.conf.

Unfortunately, at least under OpenStack, the nameserver information is not interface-scoped so it is not *possible* to correctly configure the interface configuration files.

The solution in this case is to ensure that NM will not attempt to update /etc/resolv.conf. The simplest way of doing this is to drop a file into /etc/NetworkManager/conf.d containing:

[main]
dns=none

This will prevent NetworkManager from managing /etc/resolv.conf.

Related branches

~rmccabe/cloud-init:bug1693251

Merged into cloud-init:master at revision 67bab5bb804e2346673430868935f6bbcdb88f13

Scott Moser: Approve on 2017-06-12

Lars Kellogg-Stedman (community): Approve on 2017-06-08

Server Team CI bot: Approve (continuous-integration) on 2017-06-08

Revision history for this message

Lars Kellogg-Stedman (larsks) wrote on 2017-05-24:

See also:

https://bugs.launchpad.net/nova/+bug/1693265

Revision history for this message

Lars Kellogg-Stedman (larsks) wrote on 2017-05-26:

We should probably make this behavior conditional so that we only set dns=none IF we are populating /etc/resolv.conf.

Scott Moser (smoser) on 2017-06-07

Changed in cloud-init:
status:	New → Confirmed
importance:	Undecided → Medium
assignee:	nobody → Ryan McCabe (rmccabe)

Scott Moser (smoser) on 2017-06-12

Changed in cloud-init:
status:	Confirmed → Fix Committed

Revision history for this message

Victor Costan (costan) wrote on 2017-09-09:

Please consider the following changes to the NetworkManager configuration.

1. Use 95 or 98 instead of 99 in /etc/NetworkManager/conf.d/xx-cloud-init.conf, so I can override the setting if I need to.

2. Don't generate /etc/NetworkManager/conf.d/99-cloud-init.conf if manage_resolv_conf [1] is explicitly set to False.

Long story short, I have a situation where I'd rather have NetworkManager manage my resolv.conf file. With the second suggestion, I'd have spent less time debugging. With the first suggestion, my fix would have been more elegant.

Thank you very much for your work on cloud-init!

[1] http://cloudinit.readthedocs.io/en/latest/topics/modules.html#resolv-conf