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

5 files changed, 33 insertions, 14 deletions

diff --git a/cloudinit/config/cc_set_hostname.py b/cloudinit/config/cc_set_hostname.py
index d4017478..5a59dc32 100644
--- a/cloudinit/config/cc_set_hostname.py
+++ b/cloudinit/config/cc_set_hostname.py
@@ -19,7 +19,10 @@ A hostname and fqdn can be provided by specifying a full domain name under the
 key, and the fqdn of the cloud wil be used. If a fqdn specified with the
 ``hostname`` key, it will be handled properly, although it is better to use
 the ``fqdn`` config key. If both ``fqdn`` and ``hostname`` are set,
-it is distro dependent whether ``hostname`` or ``fqdn`` is used.
+it is distro dependent whether ``hostname`` or ``fqdn`` is used,
+unless the ``prefer_fqdn_over_hostname`` option is true and fqdn is set
+it will force the use of FQDN in all distros, and if false then it will
+force the hostname use.
 
 This module will run in the init-local stage before networking is configured
 if the hostname is set by metadata or user data on the local system.
@@ -38,6 +41,7 @@ based on initial hostname.
 **Config keys**::
 
     preserve_hostname: <true/false>
+    prefer_fqdn_over_hostname: <true/false>
     fqdn: <fqdn>
     hostname: <fqdn/hostname>
 """
@@ -62,6 +66,14 @@ def handle(name, cfg, cloud, log, _args):
         log.debug(("Configuration option 'preserve_hostname' is set,"
                    " not setting the hostname in module %s"), name)
         return
+
+    # Set prefer_fqdn_over_hostname value in distro
+    hostname_fqdn = util.get_cfg_option_bool(cfg,
+                                             "prefer_fqdn_over_hostname",
+                                             None)
+    if hostname_fqdn is not None:
+        cloud.distro.set_option('prefer_fqdn_over_hostname', hostname_fqdn)
+
     (hostname, fqdn) = util.get_hostname_fqdn(cfg, cloud)
     # Check for previous successful invocation of set-hostname
 
diff --git a/cloudinit/config/cc_update_hostname.py b/cloudinit/config/cc_update_hostname.py
index d5f4eb5a..f4120356 100644
--- a/cloudinit/config/cc_update_hostname.py
+++ b/cloudinit/config/cc_update_hostname.py
@@ -27,6 +27,7 @@ is set, then the hostname will not be altered.
 **Config keys**::
 
     preserve_hostname: <true/false>
+    prefer_fqdn_over_hostname: <true/false>
     fqdn: <fqdn>
     hostname: <fqdn/hostname>
 """
@@ -45,6 +46,13 @@ def handle(name, cfg, cloud, log, _args):
                    " not updating the hostname in module %s"), name)
         return
 
+    # Set prefer_fqdn_over_hostname value in distro
+    hostname_fqdn = util.get_cfg_option_bool(cfg,
+                                             "prefer_fqdn_over_hostname",
+                                             None)
+    if hostname_fqdn is not None:
+        cloud.distro.set_option('prefer_fqdn_over_hostname', hostname_fqdn)
+
     (hostname, fqdn) = util.get_hostname_fqdn(cfg, cloud)
     try:
         prev_fn = os.path.join(cloud.get_cpath('data'), "previous-hostname")
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