cloud-init

Debian 10/9/8 DNS configuration bug

Bug #1850310 reported by Dmitry Shemin on 2019-10-29

This bug affects 2 people

Affects		Status	Importance	Assigned to	Milestone
	cloud-init	Expired	Medium	Unassigned

Bug Description

I use cloud-init with NoCloud data source for configuring my VM's and got strange bug with DNS configuration on official Debian images like https://cdimage.debian.org/cdimage/openstack/current-10/debian-10-openstack-amd64.qcow2.

My network config:

```
version: 2
ethernets:
  eth0:
    set-name: eth0
    match:
      macaddress: <MAC address>
    addresses: [ <IP address> ]
    gateway4: <GATEWAY ADDRESS>
    nameservers:
      addresses: [8.8.8.8,8.8.4.4]
```

After creating new VM I got next configuration in /etc/network/interfaces.d/50-cloud-init.cfg which is seems ok:

```
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
    address 10.52.240.11/16
    dns-nameservers 8.8.8.8 8.8.4.4
    gateway 10.52.1.1
```

But /etc/resolv.conf contains:

```
nameserver 127.0.0.1
```

Which leads to the fact that I can’t resolve any domain name, for example:
```
# ping google.com
ping: google.com: Temporary failure in name resolution
```

See original description

Revision history for this message

Dmitry Shemin (dshemin) wrote on 2019-10-29:

cloud-init.tar.gz Edit (42.5 KiB, application/x-tar)

Dmitry Shemin (dshemin) on 2019-10-29

description:

updated

Revision history for this message

Ryan Harper (raharper) wrote on 2019-10-30:

Thanks for filing the bug.

Cloud-init itself does not render /etc/resolv.conf on Ubuntu/Debian; In Ubuntu, the resolvconf package is installed which handles maintain /etc/resolv.conf.

Looking at:

https://cdimage.debian.org/cdimage/openstack/current-10/debian-10-openstack-amd64-packages.list

resolvconf package is not present, hence the bug. I would suggest that the images include this package.

That said, cloud-init could detect if resolvconf is not present and render resolv.conf directly.

Changed in cloud-init:
importance:	Undecided → Medium
status:	New → Triaged

Revision history for this message

Adam Conrad (adconrad) wrote on 2019-10-30:

> In Ubuntu, the resolvconf package is installed which handles maintain /etc/resolv.conf.

This hasn't been true for years. That said, it's still handled "magically" today, just that now we do it with systemd-resolved.

Revision history for this message

Ryan Harper (raharper) wrote on 2019-10-30:

@Adam,

In the context of Ubuntu images which still use ifupdown by default (Xenial); they also include resolvconf which is what manages resolv.conf.

As you note, newer Ubuntu uses systemd-resolved as replacement for resolvconf; cloud-init on Ubuntu does not directly render contents into /etc/resolv.conf for these reasons.

Revision history for this message

Dmitry Shemin (dshemin) wrote on 2019-10-30:

The documentation says that the 'resolvconf' package is optional for Debian. https://wiki.debian.org/NetworkConfiguration#Defining_the_.28DNS.29_Nameservers
So temporarily I used 'systemd-resolved' for DNS configuration by adding this line to my user data:

```
runcmd:
- |
   cat << EOL > /etc/systemd/resolved.conf
   [Resolve]
   DNS=8.8.8.8
   EOL
- |
   cat << EOL > /etc/resolv.conf
   nameserver 127.0.0.53
   EOL
- systemctl enable systemd-resolved
- systemctl start systemd-resolved
```

But I think it's worth doing something about it.

Revision history for this message

Brian King (inflatador) wrote on 2020-05-29:

I'm affected as well. Running an Openstack cloud with the config-drive and static IP information. The DNS servers are in the network-data.json file, but cloud-init on Debian 10 does not set the DNS servers unless the resolvconf package is present.

Revision history for this message

TJ (zimmertr) wrote on 2020-08-26:

I'm affected as well. Got around this like so:

write_files:
  - path: /etc/resolvconf/resolv.conf.d/base
    content: nameserver 192.168.1.100
runcmd:
  - [ systemctl, restart, resolvconf ]