add prefer_fqdn_over_hostname config option (#859)

the above option allows the user to control the behavior of a distro
hostname selection if both short hostname and FQDN are supplied.
If `prefer_fqdn_over_hostname` is true the FQDN will be selected as
hostname; if false the hostname will be selected

LP: #1921004

3 files changed, 12 insertions, 13 deletions

diff --git a/cloudinit/distros/__init__.py b/cloudinit/distros/__init__.py
index 220bd11f..8b8a647d 100755
--- a/cloudinit/distros/__init__.py
+++ b/cloudinit/distros/__init__.py
@@ -79,6 +79,7 @@ class Distro(persistence.CloudInitPickleMixin, metaclass=abc.ABCMeta):
     shutdown_options_map = {'halt': '-H', 'poweroff': '-P', 'reboot': '-r'}
 
     _ci_pkl_version = 1
+    prefer_fqdn = False
 
     def __init__(self, name, cfg, paths):
         self._paths = paths
@@ -131,6 +132,9 @@ class Distro(persistence.CloudInitPickleMixin, metaclass=abc.ABCMeta):
     def get_option(self, opt_name, default=None):
         return self._cfg.get(opt_name, default)
 
+    def set_option(self, opt_name, value=None):
+        self._cfg[opt_name] = value
+
     def set_hostname(self, hostname, fqdn=None):
         writeable_hostname = self._select_hostname(hostname, fqdn)
         self._write_hostname(writeable_hostname, self.hostname_conf_fn)
@@ -259,6 +263,9 @@ class Distro(persistence.CloudInitPickleMixin, metaclass=abc.ABCMeta):
     def _select_hostname(self, hostname, fqdn):
         # Prefer the short hostname over the long
         # fully qualified domain name
+        if util.get_cfg_option_bool(self._cfg, "prefer_fqdn_over_hostname",
+                                    self.prefer_fqdn) and fqdn:
+            return fqdn
         if not hostname:
             return fqdn
         return hostname
diff --git a/cloudinit/distros/freebsd.py b/cloudinit/distros/freebsd.py
index dde34d41..9659843f 100644
--- a/cloudinit/distros/freebsd.py
+++ b/cloudinit/distros/freebsd.py
@@ -27,12 +27,7 @@ class Distro(cloudinit.distros.bsd.BSD):
     pkg_cmd_remove_prefix = ["pkg", "remove"]
     pkg_cmd_update_prefix = ["pkg", "update"]
     pkg_cmd_upgrade_prefix = ["pkg", "upgrade"]
-
-    def _select_hostname(self, hostname, fqdn):
-        # Should be FQDN if available. See rc.conf(5) in FreeBSD
-        if fqdn:
-            return fqdn
-        return hostname
+    prefer_fqdn = True  # See rc.conf(5) in FreeBSD
 
     def _get_add_member_to_group_cmd(self, member_name, group_name):
         return ['pw', 'usermod', '-n', member_name, '-G', group_name]
diff --git a/cloudinit/distros/rhel.py b/cloudinit/distros/rhel.py
index c72f7c17..0c00a531 100644
--- a/cloudinit/distros/rhel.py
+++ b/cloudinit/distros/rhel.py
@@ -50,6 +50,10 @@ class Distro(distros.Distro):
         }
     }
 
+    # Should be fqdn if we can use it
+    # See: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/5/html/deployment_guide/ch-sysconfig  # noqa: E501
+    prefer_fqdn = True
+
     def __init__(self, name, cfg, paths):
         distros.Distro.__init__(self, name, cfg, paths)
         # This will be used to restrict certain
@@ -91,13 +95,6 @@ class Distro(distros.Distro):
             }
             rhel_util.update_sysconfig_file(out_fn, host_cfg)
 
-    def _select_hostname(self, hostname, fqdn):
-        # Should be fqdn if we can use it
-        # See: https://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-sysconfig.html#s2-sysconfig-network # noqa
-        if fqdn:
-            return fqdn
-        return hostname
-
     def _read_system_hostname(self):
         if self.uses_systemd():
             host_fn = self.systemd_hostname_conf_fn