Docker-mdns-helper

This service publishes CNAME records pointing to the local host over multicast DNS using the Avahi daemon found in all major Linux distributions. Useful as a poor-man's service discovery or as a helper for named virtual-hosts in development environments.

Since Avahi is compatible with Apple's Bonjour, these names are usable from MacOS X and Windows too.

This works well with Traefik and Docker-Dashy-Helper

Git repository of the Docker distribution is on Github Docker-mDNS-Helper

TL;DR

It works out of the box, just:

• Check that Avahi is installed on your system. If not, install it as root: apt install avahi-daemon for a Debian or Ubuntu system
• Change the configuration in your /etc/avahi/avahi-daemon.conf file: uncomment or add enable-dbus=yes
• Restart avahi. Type as root: service avahi-daemon restart
• Launch docker-mdns-helper:

$ docker run -d --name=mdns -v /var/run/dbus/system_bus_socket:/var/run/dbus/system_bus_socket -v /var/run/docker.sock:/var/run/docker.sock stefapi/docker-mdns-helper:latest

That's all !

Configuration

All the configuration is read from container labels (Like Traefik) and the Dashy configuration file is only written if the labels have changed.

CNAMES definition

CNAMES are defined by the following parameters:

docker-mdns.enable label conditions the following labels. If set to true the labels defined hereunder will be taken into account. if docker-mdns.enable is not specified, the default behavior is to enable the container definition unless the --disable parameter is specified when launching.

It reads the same container labels as Traefik to define CNAMES e.g. :

-l 'traefik.http.routers.r1.rule=Host(`r1example.local`)'
-l 'traefik.https.routers.r1.rule=Host(`r2example.local`, `alterdomain.local`)'

CNAMES may be personalised by using the docker-mdns.domain label like this:

-l 'docker-mdns.domain=r3example.com'

WARNING: Sub domains ( like sub.example.local ) seems not to work on all platforms. Use domains instead (like sub-example.local)

Command line arguments

Docker-mdns-helper has no mandatory parameter.

Optional parameter -d or --disable disables the automatic addition of docker containers to Dashy. You have to put the label docker-mdns.enable=true for each container to be added.

Optional parameter -D or --daemon launches the program as a daemon. Only necessary if using it with systemd on host machine.

Optional parameter -l or --log defines the filename to use to write logs to.

Optional parameter -r or --reset when active, all domains which are no more published with a Treafik label or docker-mdns.domain label are removed from avahi. During the reconfiguration no domain published by docker-mdns-helper will be published causing a temporary domain failure

Optional parameter -t or --ttl defines ttl of CNAMES publication. Default 60 seconds.

Optional parameter -w or --wait defines pause between CNAMES scans on Docker. Default 5 seconds.

Optional parameter -v or --verbose increase the level of verbosity of output.

Optional parameter -f or --force publishes a CNAME without prior existence test. Accelerates the publication of CNAMES but if CNAMES are already published, this may crash Avahi.

Following all theses options you could pass a list of CNAMES to publish

Installing

docker pull stefapi/docker-mdns-helper

Currently there are AMD64 based builds.

Building

Get git repository:

git pull https://github.com/stefapi/docker-mdns-helper

Build Docker file:

docker build .

Running

You have to attach 2 volumes:

-v /var/run/docker.sock:/var/run/docker.sock

-v /var/run/dbus/system_bus_socket:/var/run/dbus/system_bus_socket

First is used to read docker configuration and the second is used to communicate with Avahi on host system

Free Sample of container lauch:

$ docker run -d --name=mdns -v /var/run/dbus/system_bus_socket:/var/run/dbus/system_bus_socket -v /var/run/docker.sock:/var/run/docker.sock stefapi/docker-mdns-helper:latest -r domain.local anotherdomain.local