How do containers use networking.useHostResolvConf?

deliciouslytyped · February 4, 2020, 12:49pm

As far as I can tell, my containers use the host resolv.conf by default, which was an issue when trying to use networking.nameservers, because the host config would override the manual configuration. I figured this out by accidentally running across resolvconf -l.

# resolvconf -l
# resolv.conf from static
nameserver 192.160.0.1

# resolv.conf from host
# Generated by resolvconf
nameserver 127.0.0.1
options edns0

This is the script that looked like it was doing nothing (systemctl status network-setup.service):

#! /nix/store/715fljdrspphbdk255r729zxp4w7lcgk-bash-4.4-p23/bin/bash -e
# Set the static DNS configuration, if given.
/nix/store/2dzm0djdyh59c258vhbc1npbra0f1rdn-openresolv-3.9.2/sbin/resolvconf -m 1 -a static <<EOF
nameserver 192.168.0.1
EOF

# Set the default gateway.

I’m using extra-container (GitHub - erikarvstedt/extra-container: Run declarative NixOS containers without full system rebuilds) if that changes anything.

( slightly related; NixOS 20.03 Feature Freeze - #24 by Moredread )

tokudan · February 4, 2020, 3:35pm

Not sure if extra-container does anything else, but I guess it’s this line:

github.com

NixOS/nixpkgs/blob/4e3aa3de412249ac422272d7ee9193934e6a958f/nixos/modules/virtualisation/containers.nix#L86


      
          fi
          
          
if ! [ -e "$root/etc/machine-id" ]; then
            touch "$root/etc/machine-id"
          fi
          
          
mkdir -p -m 0755 \
            "/nix/var/nix/profiles/per-container/$INSTANCE" \
            "/nix/var/nix/gcroots/per-container/$INSTANCE"
          
          
cp --remove-destination /etc/resolv.conf "$root/etc/resolv.conf"
          
          
if [ "$PRIVATE_NETWORK" = 1 ]; then
            extraFlags+=" --private-network"
          fi
          
          
if [ -n "$HOST_ADDRESS" ]  || [ -n "$LOCAL_ADDRESS" ] ||
             [ -n "$HOST_ADDRESS6" ] || [ -n "$LOCAL_ADDRESS6" ]; then
            extraFlags+=" --network-veth"
          fi

deliciouslytyped · February 4, 2020, 4:11pm

I forgot to clarify that setting networking.useHostResolvConf = false; fixed the problem. (Or at least I’m pretty sure it did.)

Thanks tokudan! Ill take a look.

deliciouslytyped · February 4, 2020, 4:19pm

I just realized I accidentally a word in the topic;
How do containers set networking.useHostResolvConf? → How do containers use networking.useHostResolvConf?

Some additional clarification: when the resolvconf script is run, everything behaves as defined, it’s just that the from host section is what ends up in `/etc/resolv.conf".