Optionally add hostnames to known_hosts

openssh/files/ssh_known_hosts

 {#-   If there are none, the host is used directly. #}
 {%-   set names = [host_names.get(host, host)] -%}
 
+{#-   Extract the hostname from the FQDN and add it to the names. #}
+{%-   if use_hostnames is iterable -%}
+{%-     for name in names | sort -%}
+{%-       if salt["match.{}".format(hostnames_expr_form)](hostnames_target, minion_id=name) -%}
+{%-         set hostname = name.split('.')|first -%}
+{%-         if hostname not in names -%}
+{%-           do names.append(hostname) -%}
+{%-         endif -%}
+{%-       endif -%}
+{%-     endfor -%}
+{%-   endif -%}
+
 {#-   Append IP addresses and aliases (if they are not already present) #}
 {%-   for ip in (ip4 + ip6)|sort -%}
 {%-     do names.append(ip) -%}
 {%- set expr_form = salt['pillar.get']('openssh:known_hosts:expr_form', 'glob') -%}
 {%- set keys_function = salt['pillar.get']('openssh:known_hosts:mine_keys_function', 'public_ssh_host_keys') -%}
 {%- set hostname_function = salt['pillar.get']('openssh:known_hosts:mine_hostname_function', 'public_ssh_hostname') -%}
+{%- set use_hostnames = salt['pillar.get']('openssh:known_hosts:hostnames', False) -%}
+{%- set hostnames_target_default = '*' if grains['domain'] == '' else "*.{}".format(grains['domain']) -%}
+{%- set hostnames_target = salt['pillar.get']('openssh:known_hosts:hostnames:target', hostnames_target_default) -%}
+{%- set hostnames_expr_form = salt['pillar.get']('openssh:known_hosts:hostnames:expr_form', 'glob') -%}
 
 {#- Lookup IP of all aliases so that when we have a matching IP, we inject the alias name
     in the SSH known_hosts entry -#}

pillar.example

     aliases:
       - cname-to-minion.example.org
       - alias.example.org
+    # Includes short hostnames derived from the FQDN
+    # (host.example.test -> host)
+    # (Deactivated by default, because there can be collisions!)
+    hostnames: False
+    #hostnames:
+    # Restrict wich hosts you want to use via their hostname
+    # (i.e. ssh user@host instead of ssh user@host.example.com)
+    #  target: '*'  # Defaults to "*.{}".format(grains['domain']) with a fallback to '*'
+    #  expr_form: 'glob'
+    # To activate the defaults you can just set an empty dict.
+    #hostnames: {}
 
   # specify DH parameters (see /etc/ssh/moduli)
   moduli: |