How to route all subdomains to a single host using mDNS?

Question

I have a development webserver hosting as "myhost.local" which is found using Bonjour/mDNS. The server is running avahi-daemon.

The webserver also wants to handle any subdomains of itself. Eg "cat.myhost.local" and "dog.myhost.local" and "guppy.myhost.local".

Given that myhost.local is on a dynamic ip address from dhcp, is there still a way to route all requests for the subdomains to myhost.local?

I'm starting to think it not currently possible...

http://marc.info/?l=freedesktop-avahi&m=119561596630960&w=2

You can do this with the /etc/avahi/hosts file. Alternatively you can
use avahi-publish-host-name.

No, he cannot. Since he wants to define an alias, not a new hostname. I.e. he only wants to register an A RR, no reverse PTR RR. But if you stick something into /etc/avahi/hosts then it registers both, and detects a collision if the PTR RR is non-unique, which would be the case for an alias.

Answer 1

You can register additional records using the Avahi API. This example on the Avahi wiki demonstrates how to publish additional CNAME (alias) records in Python.

Answer 2

I gave it up as not possible at the time, and I haven't revisited the problem since.

My current solution is to laboriously add each subdomain of interest to the hosts file on the local machine.

Answer 3

I've solved this as best as I can with the small amount of time I assigned to this task.

But unfortunately I do not think the windows implementation of avahi/msdns/bonjour supports aliases (correct me if I am wrong with examples of how to support this).

What i did was start with the example python script provided on the avahi website :

Create : /usr/bin/avahi-announce-alias

Make it executable & Fill it with

#! /usr/bin/env python
# avahi-alias.py

import avahi, dbus
from encodings.idna import ToASCII

# Got these from /usr/include/avahi-common/defs.h
CLASS_IN = 0x01
TYPE_CNAME = 0x05

TTL = 60

def publish_cname(cname):
    bus = dbus.SystemBus()
    server = dbus.Interface(bus.get_object(avahi.DBUS_NAME, avahi.DBUS_PATH_SERVER),
            avahi.DBUS_INTERFACE_SERVER)
    group = dbus.Interface(bus.get_object(avahi.DBUS_NAME, server.EntryGroupNew()),
            avahi.DBUS_INTERFACE_ENTRY_GROUP)

    rdata = createRR(server.GetHostNameFqdn())
    cname = encode_dns(cname)

    group.AddRecord(avahi.IF_UNSPEC, avahi.PROTO_UNSPEC, dbus.UInt32(0),
        cname, CLASS_IN, TYPE_CNAME, TTL, rdata)
    group.Commit()


def encode_dns(name):
    out = []
    for part in name.split('.'):
        if len(part) == 0: continue
        out.append(ToASCII(part))
    return '.'.join(out)

def createRR(name):
    out = []
    for part in name.split('.'):
        if len(part) == 0: continue
        out.append(chr(len(part)))
        out.append(ToASCII(part))
    out.append('\0')
    return ''.join(out)

if __name__ == '__main__':
    import time, sys, locale
    for each in sys.argv[1:]:
        name = unicode(each, locale.getpreferredencoding())
        publish_cname(name)
    try:
        # Just loop forever
        while 1: time.sleep(60)
    except KeyboardInterrupt:
        print "Exiting"

This script handles the announcement of each individual alias, and will remain running until you kill it. (because of this, we need to create another script which I've shown below)

Create text file /etc/avahi/aliases

This we use to store aliases to this machine one per line

Create directory /etc/avahi/aliases.d/

I haven't actually made use of this in any of the scripts i show here yet, but for those enterprising individuals out there, you can see what needs to be done.

The idea is that you can group aliases into separate text files (which will make more sense when you deal with virtual hosts in apache), this is something many daemon applications on *nix already provide (apache and apt are just two examples).

Create /usr/bin/avahi-announce-alias

Make it executable and fill it with

#!/usr/bin/env python

import os, sys
from subprocess import Popen


def ensure_file (path):
    """
        Looks for  file at provided path, creates it if it does not exist.
        Returns the file.
    """
    rfile = None    
    if not os.path.exists(path) and os.path.isfile(path) :
        rfile = open(path,"w+");
        print("ensuring file : %s " % path)

    print("file ensured : %s " % path)
    return rfile


command = '/usr/bin/avahi-announce-alias'
alias_pid_path = "/tmp/avahi-aliases.pid"
alias_file_path = "/etc/avahi/aliases"

alias_file = open(alias_file_path)
if not os.path.exists(alias_pid_path) :
    open(alias_pid_path,"w").close()

alias_pid = open(alias_pid_path,"r")


for line in alias_pid :
    txt = line.strip('\n')
    if len(txt) > 0 :
        print("kill %s" % txt )
        os.system("kill %s" % txt)          
alias_pid.close()
alias_pid = open(alias_pid_path,"w+")

for line in alias_file :
    txt = line.strip('\n')
    if len(txt) > 0 :
        print("publishing : << %s >>" % txt)
        process = Popen([command, txt])
        alias_pid.write("%s\n" % str(process.pid))    
alias_pid.close()

print("done")

It is by no means meant to be the pinnacle of python programming, so feel free to make improvements where you see fit.

Usage

If our hostname was "server" and the avahi-hostname was "server.local", then we could fill up the /etc/avahi/aliases text file with your extra hostnames like so :

deluge.server.local
username.server.local
accounts.server.local
something-else.server.local
another.hostname.home

(but really, I'm pretty sure you could have any hostname in there providing you made sure it did not already exist on the network, which is why i just create 'subdomains' of the normal avahi hostname)

Then we run :

sudo avahi-publish-aliases

My main reason for setting this up was to facilitate easier simulation of django & drupal website development on my laptop.

Caveats

My only disappointment is that the windows implementation of Bonjour/Avahi does not support the aliases that this implementation announces, it will only see the main avahi hostname normally announced (ie server.local in our example above).