fix(matrix): write a static resolv.conf for tuwunel (eval-proven; #1500)

#1485's simplified fix turned off useHostResolvConf and trusted resolvconf
to honour networking.nameservers, but that is a runtime resolvconf behaviour
we couldn't verify at eval time — and it STILL came up with an empty
/etc/resolv.conf in practice, so tuwunel kept failing the resolver init and
matrix stayed down (#1500).

Take resolvconf out of the loop entirely: resolvconf.enable = false plus an
explicit environment.etc."resolv.conf" that writes nameserver <bridgeIp>
statically. Nothing regenerates it out from under tuwunel.

Eval-proven (unlike the prior variant): on a host with matrix+network on, the
generated container environment.etc."resolv.conf".text is
"nameserver <bridgeIp>\noptions edns0\n".
This commit is contained in:
atlas 2026-06-07 21:59:01 +02:00 committed by mara
commit 2efd9c4944

View file

@ -342,25 +342,28 @@ in
# tuwunel hard-fails to boot if `/etc/resolv.conf` has no
# `nameserver` line (`Failed to configure DNS resolver ... no
# nameservers found in config` → exit 1). This declarative
# nixos-container had it come up EMPTY (just `options edns0`)
# even with `networking.nameservers` set: the nixos-container
# default `useHostResolvConf = true` puts in-container resolvconf
# in host-tracking mode, which ignores `networking.nameservers`
# and never receives the host's resolv.conf across the
# shared-netns boundary — so resolvconf regenerates an empty file
# and tuwunel dies at boot.
# nixos-container comes up with an EMPTY resolv.conf even with
# `networking.nameservers` set: the nixos-container default
# `useHostResolvConf = true` puts in-container resolvconf in
# host-tracking mode (ignores `networking.nameservers`, and never
# gets the host file across the shared-netns boundary), so it
# regenerates an empty file and tuwunel dies at boot.
#
# When the hive network module is on, turn off host-tracking so
# resolvconf honours `networking.nameservers`, pointing the
# resolver at the dnsmasq the network module runs at `bridgeIp`.
# The earlier fix turned host-tracking off and trusted resolvconf
# to honour `networking.nameservers` — but that's a RUNTIME
# resolvconf behaviour, not verifiable at eval time, and it STILL
# came up empty in practice (#1500). So take resolvconf out of the
# loop entirely and write a STATIC `/etc/resolv.conf` from
# `bridgeIp` that nothing regenerates. Eval-proven: the generated
# `environment.etc."resolv.conf".text` is `nameserver <bridgeIp>`.
# This container always shares the host netns
# (`privateNetwork = false`), so it reaches `bridgeIp` whether or
# not `isolateContainers` is set. With the network module off,
# inherit the host's resolv.conf (which carries the host
# resolver). See `docs/network.md`.
# (`privateNetwork = false`), so it reaches `bridgeIp` regardless
# of `isolateContainers`. Network module off → inherit the host's
# resolv.conf. See `docs/network.md`.
networking = lib.mkMerge [
(lib.mkIf networkCfg.enable {
useHostResolvConf = lib.mkForce false;
resolvconf.enable = lib.mkForce false;
nameservers = [ networkCfg.bridgeIp ];
})
(lib.mkIf (!networkCfg.enable) {
@ -368,6 +371,16 @@ in
})
];
# resolvconf is disabled above, so write the static resolver file
# explicitly — NixOS won't synthesise one from `nameservers` once
# resolvconf is off, and this is the file tuwunel parses at boot.
environment.etc = lib.mkIf networkCfg.enable {
"resolv.conf".text = ''
nameserver ${networkCfg.bridgeIp}
options edns0
'';
};
services.matrix-tuwunel = {
enable = true;
package = cfg.package;