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fix(mdns): publish via host avahi over D-Bus (not a second daemon)

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A container running its own avahi-daemon collides with the host's on :5353.
Instead publish to the host avahi over its mounted D-Bus socket using avahi-tools
(avahi-publish). Needs apparmor=unconfined (docker-default blocks the D-Bus
publish). Documented host prereqs incl. allow-interfaces for multi-bridge hosts.

Tested: publish reaches host avahi and registers the names; on hosts with many
docker bridges avahi self-collides until restricted to the LAN interface.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Oier Bravo
2026-05-24 06:03:26 +02:00
parent de75a2ca1d
commit c7151b7333
3 changed files with 35 additions and 20 deletions
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9
docker/avahi/Dockerfile
View File

@@ -1,8 +1,9 @@
# Self-contained mDNS responder: publishes the stack's service names on .local
# so guests resolve them with zero DNS/client config (macOS/Linux native;
# Windows needs Bonjour). Used only when ENABLE_MDNS=true and BASE_DOMAIN=*.local.
# Publishes the stack's service names on .local via the HOST's avahi-daemon
# (over its D-Bus socket — no second daemon, avoids the :5353 collision).
# Requires the host to run avahi-daemon and the socket to be mounted (see
# docker-compose.avahi.yml). Used when ENABLE_MDNS=true and BASE_DOMAIN=*.local.
FROM alpine:3.20
RUN apk add --no-cache avahi dbus
RUN apk add --no-cache avahi-tools
COPY entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh
ENTRYPOINT ["/entrypoint.sh"]

24
docker/avahi/entrypoint.sh
View File

@@ -1,7 +1,7 @@
#!/bin/sh
# Publish A records for the stack's service names over mDNS (.local).
# Requires host networking (mDNS is link-local multicast). One avahi-publish
# per name; if any dies the container exits so Docker restarts it.
# Publish A records for the stack's service names on .local via the HOST's
# avahi-daemon (reached over its mounted D-Bus socket). One avahi-publish per
# name; if any drops the container exits so Docker restarts it.
set -eu
: "${BASE_DOMAIN:?BASE_DOMAIN unset}"
@@ -12,21 +12,21 @@ case "$BASE_DOMAIN" in
*) echo "WARN: mDNS resolves only .local — BASE_DOMAIN=$BASE_DOMAIN will NOT be discoverable via avahi. Set BASE_DOMAIN=*.local to use mDNS." >&2 ;;
esac
mkdir -p /run/dbus
rm -f /run/dbus/pid /run/dbus/system_bus_socket 2>/dev/null || true
dbus-daemon --system
for _ in 1 2 3 4 5; do [ -S /run/dbus/system_bus_socket ] && break; sleep 1; done
avahi-daemon --daemonize --no-chroot
sleep 2
bus="${DBUS_SYSTEM_BUS_ADDRESS:-unix:path=/run/dbus/system_bus_socket}"
sock=${bus#unix:path=}
if [ ! -S "$sock" ]; then
echo "ERROR: host D-Bus socket '$sock' not found. Mount the host's" >&2
echo " /run/dbus/system_bus_socket and ensure avahi-daemon runs on the host." >&2
exit 1
fi
export DBUS_SYSTEM_BUS_ADDRESS="$bus"
pids=""
for n in "$BASE_DOMAIN" "auth.$BASE_DOMAIN" "packwiz.$BASE_DOMAIN" "mc.$BASE_DOMAIN"; do
echo "mDNS publish: $n -> $HOST_LAN_IP"
echo "mDNS publish (host avahi): $n -> $HOST_LAN_IP"
avahi-publish -a "$n" "$HOST_LAN_IP" &
pids="$pids $!"
done
# Block on the publishers; exit (→ restart) if one drops.
# shellcheck disable=SC2086
wait -n $pids 2>/dev/null || wait