Bug#1091864: tech-ctte: Avahi and systemd-resolved cannot a run mDNS responder at the same time

[Helmut Grohne]

Hi,

we had a CTTE meeting today and consensus was that nor more information
would need to be gathered before forming a decision. We saw the
following consensus items:

 * It is not clear that Avahi is a good option for mDNS long term.
   Therefore, a decision should be limited to Debian trixie.

   For instance, Lennart Poettering was an Avahi developer and is now
   working on resolved. The Avahi code base is showing signs of age, but
   it may pose to be predominant for more time. We cannot tell at this
   time.

 * The Avahi still is predominant and it should be the default in Debian
   trixie.

   Avahi is the default in Fedora and other distributions.

 * While it would be possible to treat mDNS resolution independently
   from mDNS publishing in the ballot, outcomes where they are handled
   differently tend to cause more confusion and we rather want to have
   them configured uniformly.

   Fedora attempted to use both for mDNS resolution, but then settled on
   deferring it to Avahi only, because resolved would need to be enabled
   for each interface individually and would inhibit Avahi from being
   considered for resolution making .local resolution practically fail.

 * Disagreement resides about whether systemd-resolved should perform
   mDNS resolution or publishing in its default configuration when Avahi
   is not installed.

If anyone disagrees with any of these consensus items, please tell now.
Based on these agreements, I am proposing a resolution with three
options (under constitution 6.3.1.1). There is a slight change in option
(A). It no longer mandates a mechanism, but merely suggests it.

(S) The CTTE reaffirms that avahi-daemon is the default mDNS
    implementation in Debian trixie. Therefore systemd-resolved should
    disable the mDNS functionality in its default installation in Debian
    trixie.
    (Requires a 3:1 majority overruling a developer.)

(A) The CTTE reaffirms that avahi-daemon is the default mDNS
    implementation in Debian trixie. This does not preclude other
    resolvers such as systemd-resolved operating when avahi-daemon is
    not installed. To achieve this, avahi-daemon should disable
    systemd-resolved e.g. using a resolved configuration file.
    (Requires a 3:1 majority overruling a developer.)

(F) Further discussion

Unless I receive notable objections, I will call for a vote in three
days.

Helmut
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