Problem with DNS resolution within a container

LXD
1

Hi,
I run LXD 5.21 on Ubuntu 24.04. Everything is as simple as possible: the server has one Ethernet interface configured for DHCP. DNS resolving works well on the server.
I’ve created a Debian 12 container instance from my image that is configured for ifupdown instead of systemd-networkd. Unfortunately the DNS resolving doesn’t work:

lxc exec tst3 -- ping yahoo.com
ping: yahoo.com: Temporary failure in name resolution

I have never had any issues with this image on LXD 3.0.3 on Ubuntu 18.04.
In the past, the /run/systemd/resolve/stub-resolv.conf was generated as the following, and resolving worked well:

domain lxd
search lxd
nameserver <IP of lxdbr0>

In Ubuntu 24.04/LXD 5.21 the /run/systemd/resolve/stub-resolv.conf is generated differently:

nameserver 127.0.0.53
options edns0 trust-ad
search  .

and the resolving doesn’t work:

ping yahoo.com
ping: yahoo.com: Temporary failure in name resolution

It is possible to define a DNS server statically in resolv.conf, but then it will be problematic to move the container to another server.

The debian12 container from images.lxd.canonical.com is configured for systemd-networkd and doesn’t have the resolving problem. However, I would like to use the same image for creating containers in LXD 3.0.3 and also on LXD 5.21. The systemd-networkd doesn’t work on old systems…
Any help is appreciated.

Leonid

2

Where is the DNS configuration in your container? Please can you show me the configuration files your older image is using?

Thanks

3

Hello Thomas,
Eventually, I uninstalled the systemd-resolved package in my custom Debian 12 LXD image and it solved the problem. Now LXD creates /etc/resolv.conf

domain lxd
search lxd
nameserver 10.144.113.1

when the container is created and the resolving works well.
In contrast, when the systemd-resolved is installed, the /etc/resolv.conf is a symbolic link to /run/systemd/resolve/stub-resolv.conf that contains:

nameserver 127.0.0.53
options edns0 trust-ad
search  .

Such configuration works well when system-networkd is used. But in my custom image, I use ifupdown because of reasons. And then the resolving doesn’t work. As a workaround, I uninstalled the systemd-resolved package and the problem was solved.
Thank you.