How to configure the Home Assistant Docker container for mDNS?

Configuration
1

I am looking to get the Home Assistant Docker container (specifically raspberrypi4-homeassistant) configured to resolve mDNS names, like the one generated by an Eagle-200 device.

On my host Raspberry Pi 4, I have no issues resolving the DNS name.
However, within the Docker container on that host, I cannot resolve it.
(I have no issues pinging public internet domains/DNS names from the host and the container.)

Is this a configuration that can be somehow added to the Home Assistant Docker image? Or only something that can be configured myself after pulling/running the Home Assistant Docker image?

# Successful ping with DNS name from host machine
pi@raspberrypi ~> ping eagle-xxxxxx.local
PING eagle-xxxxxx.local (192.168.1.6) 56(84) bytes of data.
64 bytes from 192.168.1.6 (192.168.1.6): icmp_seq=1 ttl=64 time=0.510 ms
64 bytes from 192.168.1.6 (192.168.1.6): icmp_seq=2 ttl=64 time=0.314 ms
^C
--- eagle-xxxxxx.local ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1002ms
rtt min/avg/max/mdev = 0.314/0.412/0.510/0.098 ms


# Unsuccessful ping with DNS name from Docker container on host machine
pi@raspberrypi ~> docker exec -it homeassistant /bin/bash
bash-5.1# ping eagle-xxxxxx.local
ping: bad address 'eagle-xxxxxx.local'
bash-5.1# ping 192.168.1.6
PING 192.168.1.6 (192.168.1.6): 56 data bytes
64 bytes from 192.168.1.6: seq=0 ttl=64 time=0.720 ms
64 bytes from 192.168.1.6: seq=1 ttl=64 time=0.829 ms
^C
--- 192.168.1.6 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.720/0.774/0.829 ms


# Confirmed that Docker copied in the host's nameserver correctly
pi@raspberrypi ~> cat /etc/resolv.conf
# Generated by resolvconf
nameserver 192.168.1.1
...
pi@raspberrypi ~> docker exec -it homeassistant /bin/bash
bash-5.1# cat /etc/resolv.conf
# Generated by resolvconf
nameserver 192.168.1.1
...
1 Like
2

What kind of HA installation?
If it’s plain “Container”, be sure to use host networking or the multicast packets won’t go through.

3

Yes, it is a container installation, I thought that was the only Docker-centric one on Raspberry Pi.

Yes, the Docker command is copied from that page, docker run ... --network=host ..., which I believe allows the container to copy in the host’s /etc/resolv.conf file.

4

Hi! I am having the same issue. did you manage to figure this out?

1 Like
5

I did not :frowning:

6

Same problem :frowning:
Any news?

7

For me the solution was to include this on creating the container:

-v /volume2/docker2/homeassistant/config/resolv.conf:/etc/resolv.conf \

or in Docker compose:

volumes:
- “/volume2/docker2/homeassistant/config/resolv.conf:/etc/resolv.conf”

On the host, in the /etc/resolv.conf file, include your DNS server on the forst line:
nameserver 192.168.x.xxx

That worked for me.

8

For whoever comes here in relation to the title:

  1. That doesn’t do anything in relation mDns; mDns doesn’t use any DNS server, it’s a multicast based protocol
  2. That bind mount is specific to @WeterPeter. Nobody knows what is in the “/volume2/docker2/homeassistant/config/resolv.conf” file he mounts inside the HA container :wink:
  3. That breaks docker’s own DNS resolution mechanism. Your mileage might vary, here…

Bottom-line: Happy it works for him, but don’t try this at home :slight_smile:

9

For anyone that might stumble on this.
Should you decide not to use network_mode: host and instead make your own network for the container. The mDNS can be made working should used avahi reflectors in the configuration.
Just enable them in /etc/avahi/avahi-daemon.conf and restart the avahi daemon systemctl restart avahi-daemon.

2 Likes
10

Thanks, it helped. In gratitude, i detailed the changes for those users who are somewhat noobs with the console
I edited:

sudo nano /etc/avahi/avahi-daemon.conf

as show below:

[reflector]
enable-reflector=yes

then restarted the daemon:

sudo systemctl restart avahi-daemon

And now i can operate with Sonoff integrations in “local mode” without

--network=host
11

For the sake of completeness, be aware that enabling the reflector in the avahi configuration makes that mDNS will be reflected on ALL your interfaces.

While it is not a problem as such for most people, keep in mind that if you have more than one interface (e.g. a separate IoT subnet or VLAN), you can only have one reflector on these networks, otherwise they will start to re-advertise each other announcements!