feat: check for create_hostname_file key before writing /etc/hostname…

… (SC-1588) (#4330)

Some users would like to be able to bring up their systems without
automatically creating /etc/hostname if it does not exist already.
On distros with systemd, the hostname/hostnamectl command can be
used to set the hostname transiently (which does not create
/etc/hostname).  To support this without changing previous behavior
(that cloud-init will set the hostname statically and create
/etc/hostname if it does not already exist), this change proposes a
new key preserve_etchostname_state which is true, sets the hostname
transiently and if not present or False, sets it statically.

This change does not affect BSD or OpenBSD (or any distros that
inherit their _write_hostname), as their hostname management does
not use an /etc/hostname file.

Co-authored-by: Catherine Redfield <catherine.redfield@canonical.com>

cloudinit/config/cc_set_hostname.py

@@ -96,6 +96,13 @@ def handle(name: str, cfg: Config, cloud: Cloud, args: list) -> None:
     if hostname_fqdn is not None:
         cloud.distro.set_option("prefer_fqdn_over_hostname", hostname_fqdn)
 
+    # Set create_hostname_file in distro
+    create_hostname_file = util.get_cfg_option_bool(
+        cfg, "create_hostname_file", None
+    )
+    if create_hostname_file is not None:
+        cloud.distro.set_option("create_hostname_file", create_hostname_file)
+
     (hostname, fqdn, is_default) = util.get_hostname_fqdn(cfg, cloud)
     # Check for previous successful invocation of set_hostname
 

cloudinit/config/cc_update_hostname.py

@@ -99,6 +99,13 @@ def handle(name: str, cfg: Config, cloud: Cloud, args: list) -> None:
     if hostname_fqdn is not None:
         cloud.distro.set_option("prefer_fqdn_over_hostname", hostname_fqdn)
 
+    # Set create_hostname_file in distro
+    create_hostname_file = util.get_cfg_option_bool(
+        cfg, "create_hostname_file", None
+    )
+    if create_hostname_file is not None:
+        cloud.distro.set_option("create_hostname_file", create_hostname_file)
+
     (hostname, fqdn, is_default) = util.get_hostname_fqdn(cfg, cloud)
     if is_default and hostname == "localhost":
         # https://github.com/systemd/systemd/commit/d39079fcaa05e23540d2b1f0270fa31c22a7e9f1

cloudinit/config/schemas/schema-cloud-config-v1.json

@@ -2576,6 +2576,11 @@
         "prefer_fqdn_over_hostname": {
           "type": "boolean",
           "description": "If true, the fqdn will be used if it is set. If false, the hostname will be used. If unset, the result is distro-dependent"
+        },
+        "create_hostname_file": {
+          "type": "boolean",
+          "default": true,
+          "description": "If ``false``, the hostname file (e.g. /etc/hostname) will not be created if it does not exist. On systems that use systemd, setting create_hostname_file to ``false`` will set the hostname transiently. If ``true``, the hostname file will always be created and the hostname will be set statically on systemd systems. Default: ``true``"
         }
       }
     },
@@ -3064,6 +3069,11 @@
           "type": "boolean",
           "default": null,
           "description": "By default, it is distro-dependent whether cloud-init uses the short hostname or fully qualified domain name when both ``local-hostname` and ``fqdn`` are both present in instance metadata. When set ``true``, use fully qualified domain name if present as hostname instead of short hostname. When set ``false``, use ``hostname`` config value if present, otherwise fallback to ``fqdn``."
+        },
+        "create_hostname_file": {
+          "type": "boolean",
+          "default": true,
+          "description": "If ``false``, the hostname file (e.g. /etc/hostname) will not be created if it does not exist. On systems that use systemd, setting create_hostname_file to ``false`` will set the hostname transiently. If ``true``, the hostname file will always be created and the hostname will be set statically on systemd systems. Default: ``true``"
         }
       }
     },

cloudinit/distros/alpine.py

@@ -81,7 +81,13 @@ def _write_hostname(self, hostname, filename):
             # so lets see if we can read it first.
             conf = self._read_hostname_conf(filename)
         except IOError:
-            pass
+            create_hostname_file = util.get_cfg_option_bool(
+                self._cfg, "create_hostname_file", True
+            )
+            if create_hostname_file:
+                pass
+            else:
+                return
         if not conf:
             conf = HostnameConf("")
         conf.set_hostname(hostname)

cloudinit/distros/arch.py

@@ -119,7 +119,13 @@ def _write_hostname(self, hostname, filename):
             # so lets see if we can read it first.
             conf = self._read_hostname_conf(filename)
         except IOError:
-            pass
+            create_hostname_file = util.get_cfg_option_bool(
+                self._cfg, "create_hostname_file", True
+            )
+            if create_hostname_file:
+                pass
+            else:
+                return
         if not conf:
             conf = HostnameConf("")
         conf.set_hostname(hostname)

cloudinit/distros/debian.py

@@ -148,7 +148,13 @@ def _write_hostname(self, hostname, filename):
             # so lets see if we can read it first.
             conf = self._read_hostname_conf(filename)
         except IOError:
-            pass
+            create_hostname_file = util.get_cfg_option_bool(
+                self._cfg, "create_hostname_file", True
+            )
+            if create_hostname_file:
+                pass
+            else:
+                return
         if not conf:
             conf = HostnameConf("")
         conf.set_hostname(hostname)

cloudinit/distros/gentoo.py

@@ -183,7 +183,13 @@ def _write_hostname(self, hostname, filename):
             # so lets see if we can read it first.
             conf = self._read_hostname_conf(filename)
         except IOError:
-            pass
+            create_hostname_file = util.get_cfg_option_bool(
+                self._cfg, "create_hostname_file", True
+            )
+            if create_hostname_file:
+                pass
+            else:
+                return
         if not conf:
             conf = HostnameConf("")
 

cloudinit/distros/opensuse.py

@@ -221,18 +221,34 @@ def _set_update_method(self):
                 self.update_method = "zypper"
 
     def _write_hostname(self, hostname, filename):
+        create_hostname_file = util.get_cfg_option_bool(
+            self._cfg, "create_hostname_file", True
+        )
         if self.uses_systemd() and filename.endswith("/previous-hostname"):
             util.write_file(filename, hostname)
         elif self.uses_systemd():
-            subp.subp(["hostnamectl", "set-hostname", str(hostname)])
+            if create_hostname_file:
+                subp.subp(["hostnamectl", "set-hostname", str(hostname)])
+            else:
+                subp.subp(
+                    [
+                        "hostnamectl",
+                        "set-hostname",
+                        "--transient",
+                        str(hostname),
+                    ]
+                )
         else:
             conf = None
             try:
                 # Try to update the previous one
                 # so lets see if we can read it first.
                 conf = self._read_hostname_conf(filename)
             except IOError:
-                pass
+                if create_hostname_file:
+                    pass
+                else:
+                    return
             if not conf:
                 conf = HostnameConf("")
             conf.set_hostname(hostname)

cloudinit/distros/photon.py

@@ -93,9 +93,23 @@ def _write_hostname(self, hostname, filename):
         if filename and filename.endswith("/previous-hostname"):
             util.write_file(filename, hostname)
         else:
-            ret, _out, err = self.exec_cmd(
-                ["hostnamectl", "set-hostname", str(hostname)]
+            ret = None
+            create_hostname_file = util.get_cfg_option_bool(
+                self._cfg, "create_hostname_file", True
             )
+            if create_hostname_file:
+                ret, _out, err = self.exec_cmd(
+                    ["hostnamectl", "set-hostname", str(hostname)]
+                )
+            else:
+                ret, _out, err = self.exec_cmd(
+                    [
+                        "hostnamectl",
+                        "set-hostname",
+                        "--transient",
+                        str(hostname),
+                    ]
+                )
             if ret:
                 LOG.warning(
                     (

cloudinit/distros/rhel.py

@@ -109,7 +109,20 @@ def _write_hostname(self, hostname, filename):
             conf.set_hostname(hostname)
             util.write_file(filename, str(conf), 0o644)
         elif self.uses_systemd():
-            subp.subp(["hostnamectl", "set-hostname", str(hostname)])
+            create_hostname_file = util.get_cfg_option_bool(
+                self._cfg, "create_hostname_file", True
+            )
+            if create_hostname_file:
+                subp.subp(["hostnamectl", "set-hostname", str(hostname)])
+            else:
+                subp.subp(
+                    [
+                        "hostnamectl",
+                        "set-hostname",
+                        "--transient",
+                        str(hostname),
+                    ]
+                )
         else:
             host_cfg = {
                 "HOSTNAME": hostname,

tests/unittests/config/test_cc_set_hostname.py

@@ -259,5 +259,95 @@ def test_ignore_empty_previous_artifact_file(self):
         contents = util.load_file("/etc/hostname")
         self.assertEqual("blah", contents.strip())
 
+    def test_create_hostname_file_false(self):
+        cfg = {
+            "hostname": "foo",
+            "fqdn": "foo.blah.yahoo.com",
+            "create_hostname_file": False,
+        }
+        distro = self._fetch_distro("debian")
+        paths = helpers.Paths({"cloud_dir": self.tmp})
+        ds = None
+        cc = cloud.Cloud(ds, paths, {}, distro, None)
+        self.patchUtils(self.tmp)
+        cc_set_hostname.handle("cc_set_hostname", cfg, cc, [])
+        with self.assertRaises(FileNotFoundError):
+            util.load_file("/etc/hostname")
+
+    def test_create_hostname_file_false_arch(self):
+        cfg = {
+            "hostname": "foo",
+            "fqdn": "foo.blah.yahoo.com",
+            "create_hostname_file": False,
+        }
+        distro = self._fetch_distro("arch")
+        paths = helpers.Paths({"cloud_dir": self.tmp})
+        ds = None
+        cc = cloud.Cloud(ds, paths, {}, distro, None)
+        self.patchUtils(self.tmp)
+        cc_set_hostname.handle("cc_set_hostname", cfg, cc, [])
+        with self.assertRaises(FileNotFoundError):
+            util.load_file("/etc/hostname")
+
+    def test_create_hostname_file_false_alpine(self):
+        cfg = {
+            "hostname": "foo",
+            "fqdn": "foo.blah.yahoo.com",
+            "create_hostname_file": False,
+        }
+        distro = self._fetch_distro("alpine")
+        paths = helpers.Paths({"cloud_dir": self.tmp})
+        ds = None
+        cc = cloud.Cloud(ds, paths, {}, distro, None)
+        self.patchUtils(self.tmp)
+        cc_set_hostname.handle("cc_set_hostname", cfg, cc, [])
+        with self.assertRaises(FileNotFoundError):
+            util.load_file("/etc/hostname")
+
+    def test_create_hostname_file_false_gentoo(self):
+        cfg = {
+            "hostname": "foo",
+            "fqdn": "foo.blah.yahoo.com",
+            "create_hostname_file": False,
+        }
+        distro = self._fetch_distro("gentoo")
+        paths = helpers.Paths({"cloud_dir": self.tmp})
+        ds = None
+        cc = cloud.Cloud(ds, paths, {}, distro, None)
+        self.patchUtils(self.tmp)
+        cc_set_hostname.handle("cc_set_hostname", cfg, cc, [])
+        with self.assertRaises(FileNotFoundError):
+            util.load_file("/etc/hostname")
+
+    def test_create_hostname_file_false_photon(self):
+        cfg = {
+            "hostname": "foo",
+            "fqdn": "foo.blah.yahoo.com",
+            "create_hostname_file": False,
+        }
+        distro = self._fetch_distro("photon")
+        paths = helpers.Paths({"cloud_dir": self.tmp})
+        ds = None
+        cc = cloud.Cloud(ds, paths, {}, distro, None)
+        self.patchUtils(self.tmp)
+        cc_set_hostname.handle("cc_set_hostname", cfg, cc, [])
+        with self.assertRaises(FileNotFoundError):
+            util.load_file("/etc/hostname")
+
+    def test_create_hostname_file_false_rhel(self):
+        cfg = {
+            "hostname": "foo",
+            "fqdn": "foo.blah.yahoo.com",
+            "create_hostname_file": False,
+        }
+        distro = self._fetch_distro("rhel")
+        paths = helpers.Paths({"cloud_dir": self.tmp})
+        ds = None
+        cc = cloud.Cloud(ds, paths, {}, distro, None)
+        self.patchUtils(self.tmp)
+        cc_set_hostname.handle("cc_set_hostname", cfg, cc, [])
+        with self.assertRaises(FileNotFoundError):
+            util.load_file("/etc/hostname")
+
 
 # vi: ts=4 expandtab

tools/.github-cla-signers

@@ -25,6 +25,7 @@ bmhughes
 brianphaley
 CalvoM
 candlerb
+catmsred
 cawamata
 cclauss
 chifac08