[BUG] Cannot resolve unqualified name "salt"

[DaAwesomeP]

Description
When systemd-resolved is used to resolve names on a system, it does not resolve unqualified hosts (hosts without a domain name) into FQDNs using the machine's domain. For example, if a minion's FQDN is minion.mydomain.com, systemd-resolved will fail to resolve salt as salt.mydomain.com on that machine.

Setup

• on-prem machine
• VM (Virtualbox, KVM, etc. please specify)
• VM running on a cloud service, please be explicit and add details
• container (Kubernetes, Docker, containerd, etc. please specify)
• or a combination, please be explicit
• jails if it is FreeBSD
• classic packaging
• onedir packaging
• used bootstrap to install

Running in a OVH US VPS on Debian 11 amd64. Saltstack 3005.1 from the Saltstack repos. On this machine I disabled cloud-init, changed the FQDN, and installed salt. Nothing else was changed from the Debian 11 install given by OVH.

Steps to Reproduce the behavior

1. Setup machine that resolves using systemd-resolved, set full FQDN
2. Install Salt minion 3005.1 on machine
3. Start salt-minion

4. Nov 15 21:32:16 some-minion salt-minion[2991]: [ERROR   ] DNS lookup or connection check of 'salt' failed.
   Nov 15 21:32:16 some-minion salt-minion[2991]: [ERROR   ] Master hostname: 'salt' not found or not responsive. Retrying in 30 seconds
   

Expected behavior
Because the resolver cannot be trusted to attempt to resolve with the machine's domain, minions should try resolving both salt and salt.machinedomain.com at startup.

Screenshots
N/A

Versions Report

salt --versions-report

Salt Version:
          Salt: 3005.1
 
Dependency Versions:
          cffi: Not Installed
      cherrypy: Not Installed
      dateutil: 2.8.1
     docker-py: Not Installed
         gitdb: 4.0.5
     gitpython: 3.1.14
        Jinja2: 2.11.3
       libgit2: Not Installed
      M2Crypto: Not Installed
          Mako: Not Installed
       msgpack: 1.0.0
  msgpack-pure: Not Installed
  mysql-python: Not Installed
     pycparser: Not Installed
      pycrypto: Not Installed
  pycryptodome: 3.9.7
        pygit2: Not Installed
        Python: 3.9.2 (default, Feb 28 2021, 17:03:44)
  python-gnupg: Not Installed
        PyYAML: 5.3.1
         PyZMQ: 20.0.0
         smmap: 4.0.0
       timelib: Not Installed
       Tornado: 4.5.3
           ZMQ: 4.3.4
 
System Versions:
          dist: debian 11 bullseye
        locale: utf-8
       machine: x86_64
       release: 5.10.0-19-cloud-amd64
        system: Linux
       version: Debian GNU/Linux 11 bullseye

Additional context
Related: systemd/systemd#2514

See above link, it is apparently the correct functionality for the resolver not to resolve unqualified names.

[DaAwesomeP]

Here is the default:

salt/salt/config/__init__.py

Lines 979 to 982 in ffdf263

	DEFAULT_MINION_OPTS = immutabletypes.freeze(
	{
	"interface": "0.0.0.0",
	"master": "salt",

Since using unqualified domains goes against spec, it doesn't seem like a good default. However, configuration-less minions are fantastic. Would this be the appropriate place to change it to something like:

import socket
DEFAULT_MASTER_HOSTNAME = "salt"

def findDefaultMasterName() -> str:
    fqdn = socket.getfqdn()
    # If this machine has a domain name, use it instead of unqualified hostname
    if "." in fqdn:
        return DEFAULT_MASTER_HOSTNAME + "." + fqdn.partition(".")[2]
    # Fall back to unqualified hostname
    return DEFAULT_MASTER_HOSTNAME

DEFAULT_MINION_OPTS = immutabletypes.freeze( 
     { 
         "interface": "0.0.0.0", 
         "master": findDefaultMasterName()
         ...

Note that simply socket.getfqdn("salt") should not be used here because it actually performs a lookup.

If the above looks good then I will open a pull! Although I'm not sure in which file that function should be defined. Maybe a util file?

[OrangeDog]

Wouldn't that break the common setup of adding salt to /etc/hosts?

Also, systemd-resolved handles "salt" just fine on my system - systemd v245