How to run avahi in docker on a Linux host?

Question

I am trying to setup avahi in a docker container running on a Linux host. The purpose is to let avahi announce a service of my own and form me find the host and IP of the docker host.

So far avahi seems to run nicely in the container but I can not find my services searching from outside of my host.

I have googled alot and there are suggestions what to do but they all seems to be contradictory and/or insecure.

This is what I got so far.

docker-compose.yml

version: "3.7"
services:
    avahi:
        container_name: avahi
        build:
            context: ./config/avahi
            dockerfile: DockerFile
            network: host

DockerFile:

FROM alpine:3.13

RUN apk add --no-cache avahi avahi-tools
ADD avahi-daemon.conf /etc/avahi/avahi-daemon.conf
ADD psmb.service /etc/avahi/services/mpsu.service


ENTRYPOINT avahi-daemon --no-drop-root --no-rlimits

avahi-daemon.conf:

[server]
enable-dbus=no

psmb.service: (my service)

<!DOCTYPE service-group SYSTEM "avahi-service.dtd"> 
<service-group> 
    <name replace-wildcards="yes">PSMB</name>
    <service> <type>_mqtt._tcp</type> <port>1883</port>
        <txt-record>info=MPS Service Host</txt-record>
    </service>
</service-group>

This is from the terminal when starting avahi:

> docker-compose up                                       
Starting avahi ... done
Attaching to avahi
avahi    | avahi-daemon 0.8 starting up.
avahi    | WARNING: No NSS support for mDNS detected, consider installing nss-mdns!
avahi    | Loading service file /etc/avahi/services/mpsu.service.
avahi    | Loading service file /etc/avahi/services/sftp-ssh.service.
avahi    | Loading service file /etc/avahi/services/ssh.service.
avahi    | Joining mDNS multicast group on interface eth0.IPv4 with address 172.18.0.2.
avahi    | New relevant interface eth0.IPv4 for mDNS.
avahi    | Joining mDNS multicast group on interface lo.IPv4 with address 127.0.0.1.
avahi    | New relevant interface lo.IPv4 for mDNS.
avahi    | Network interface enumeration completed.
avahi    | Registering new address record for 172.18.0.2 on eth0.IPv4.
avahi    | Registering new address record for 127.0.0.1 on lo.IPv4.
avahi    | Server startup complete. Host name is 8f220b5ac449.local. Local service cookie is 1841391818.
avahi    | Service "8f220b5ac449" (/etc/avahi/services/ssh.service) successfully established.
avahi    | Service "8f220b5ac449" (/etc/avahi/services/sftp-ssh.service) successfully established.
avahi    | Service "PSMB" (/etc/avahi/services/mpsu.service) successfully established.

So,, how do I configure to be able to search for my service?
I would like to get the host information for the Host running docker.

Answer 1

So, I ran across this project https://gitlab.com/ydkn/docker-avahi

Dockerfile:

# base image
ARG ARCH=amd64
FROM $ARCH/alpine:3

# args
ARG VCS_REF
ARG BUILD_DATE

# labels
LABEL maintainer="Florian Schwab <[email protected]>" \
  org.label-schema.schema-version="1.0" \
  org.label-schema.name="ydkn/avahi" \
  org.label-schema.description="Simple Avahi docker image" \
  org.label-schema.version="0.1" \
  org.label-schema.url="https://hub.docker.com/r/ydkn/avahi" \
  org.label-schema.vcs-url="https://gitlab.com/ydkn/docker-avahi" \
  org.label-schema.vcs-ref=$VCS_REF \
  org.label-schema.build-date=$BUILD_DATE

# install packages
RUN apk --no-cache --no-progress add avahi avahi-tools

# remove default services
RUN rm /etc/avahi/services/*

# disable d-bus
RUN sed -i 's/.*enable-dbus=.*/enable-dbus=no/' /etc/avahi/avahi-daemon.conf

# entrypoint
ADD docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh
ENTRYPOINT [ "docker-entrypoint.sh" ]

# default command
CMD ["avahi-daemon"]

# volumes
VOLUME ["/etc/avahi/services"]

you'll have to change/uncomment ALLOW_INTERFACES and DENY_INTERFACES in /etc/avahi/avahi-daemon.conf to "allow" whatever eth port you are using. i.e.

avahi-daemon.conf:

...
use-ipv4=yes
use-ipv6=yes
allow-interfaces=eth1 # was commented out with eth0
deny-interfaces=eth0 # was commented out with eth1
...

and then you can simply run the container, with the ALLOW_INTERFACES=??? matching what was set in avahi-daemon.conf

run command:

docker run -d --restart always \
  --net=host \
  -e ALLOW_INTERFACES=eth1 \
  -v $(pwd)/services:/etc/avahi/services \
  ydkn/avahi:latest

Seems to work, I was able to ping computername.local from another computer on/connected to the router, where computername is whatever is on the terminal line, i.e. username@computername:~$

Looks like there is also a way to add a service file, mounted to /etc/avahi/services so I believe you can customize the service name to something else more useful. I need to figure out how to do that, will edit when I find out.