set_hostname: When present in metadata, set it before network bringup.

When instance meta-data provides hostname information, run
cc_set_hostname in the init-local or init-net stage before network
comes up.

Prevent an initial DHCP request which leaks the stock cloud-image default
hostname before the meta-data provided hostname was processed.
A leaked cloud-image hostname adversely affects Dynamic DNS which
would reallocate 'ubuntu' hostname in DNS to every instance brought up by
cloud-init. These instances would only update DNS to the cloud-init
configured hostname upon DHCP lease renewal.

This branch extends the get_hostname methods in datasource, cloud and
util to limit results to metadata_only to avoid extra cost of querying
the distro for hostname information if metadata does not provide that
information.

LP: #1746455

1 files changed, 53 insertions, 4 deletions

diff --git a/tests/unittests/test_handler/test_handler_set_hostname.py b/tests/unittests/test_handler/test_handler_set_hostname.py
index abdc17e7..d09ec23a 100644
--- a/tests/unittests/test_handler/test_handler_set_hostname.py
+++ b/tests/unittests/test_handler/test_handler_set_hostname.py
@@ -11,6 +11,7 @@ from cloudinit.tests import helpers as t_help
 
 from configobj import ConfigObj
 import logging
+import os
 import shutil
 from six import BytesIO
 import tempfile
@@ -19,14 +20,18 @@ LOG = logging.getLogger(__name__)
 
 
 class TestHostname(t_help.FilesystemMockingTestCase):
+
+    with_logs = True
+
     def setUp(self):
         super(TestHostname, self).setUp()
         self.tmp = tempfile.mkdtemp()
+        util.ensure_dir(os.path.join(self.tmp, 'data'))
         self.addCleanup(shutil.rmtree, self.tmp)
 
     def _fetch_distro(self, kind):
         cls = distros.fetch(kind)
-        paths = helpers.Paths({})
+        paths = helpers.Paths({'cloud_dir': self.tmp})
         return cls(kind, {}, paths)
 
     def test_write_hostname_rhel(self):
@@ -34,7 +39,7 @@ class TestHostname(t_help.FilesystemMockingTestCase):
             'hostname': 'blah.blah.blah.yahoo.com',
         }
         distro = self._fetch_distro('rhel')
-        paths = helpers.Paths({})
+        paths = helpers.Paths({'cloud_dir': self.tmp})
         ds = None
         cc = cloud.Cloud(ds, paths, {}, distro, None)
         self.patchUtils(self.tmp)
@@ -51,7 +56,7 @@ class TestHostname(t_help.FilesystemMockingTestCase):
             'hostname': 'blah.blah.blah.yahoo.com',
         }
         distro = self._fetch_distro('debian')
-        paths = helpers.Paths({})
+        paths = helpers.Paths({'cloud_dir': self.tmp})
         ds = None
         cc = cloud.Cloud(ds, paths, {}, distro, None)
         self.patchUtils(self.tmp)
@@ -65,7 +70,7 @@ class TestHostname(t_help.FilesystemMockingTestCase):
             'hostname': 'blah.blah.blah.suse.com',
         }
         distro = self._fetch_distro('sles')
-        paths = helpers.Paths({})
+        paths = helpers.Paths({'cloud_dir': self.tmp})
         ds = None
         cc = cloud.Cloud(ds, paths, {}, distro, None)
         self.patchUtils(self.tmp)
@@ -74,4 +79,48 @@ class TestHostname(t_help.FilesystemMockingTestCase):
             contents = util.load_file(distro.hostname_conf_fn)
             self.assertEqual('blah', contents.strip())
 
+    def test_multiple_calls_skips_unchanged_hostname(self):
+        """Only new hostname or fqdn values will generate a hostname call."""
+        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', {'hostname': 'hostname1.me.com'}, cc, LOG, [])
+        contents = util.load_file("/etc/hostname")
+        self.assertEqual('hostname1', contents.strip())
+        cc_set_hostname.handle(
+            'cc_set_hostname', {'hostname': 'hostname1.me.com'}, cc, LOG, [])
+        self.assertIn(
+            'DEBUG: No hostname changes. Skipping set-hostname\n',
+            self.logs.getvalue())
+        cc_set_hostname.handle(
+            'cc_set_hostname', {'hostname': 'hostname2.me.com'}, cc, LOG, [])
+        contents = util.load_file("/etc/hostname")
+        self.assertEqual('hostname2', contents.strip())
+        self.assertIn(
+            'Non-persistently setting the system hostname to hostname2',
+            self.logs.getvalue())
+
+    def test_error_on_distro_set_hostname_errors(self):
+        """Raise SetHostnameError on exceptions from distro.set_hostname."""
+        distro = self._fetch_distro('debian')
+
+        def set_hostname_error(hostname, fqdn):
+            raise Exception("OOPS on: %s" % fqdn)
+
+        distro.set_hostname = set_hostname_error
+        paths = helpers.Paths({'cloud_dir': self.tmp})
+        ds = None
+        cc = cloud.Cloud(ds, paths, {}, distro, None)
+        self.patchUtils(self.tmp)
+        with self.assertRaises(cc_set_hostname.SetHostnameError) as ctx_mgr:
+            cc_set_hostname.handle(
+                'somename', {'hostname': 'hostname1.me.com'}, cc, LOG, [])
+        self.assertEqual(
+            'Failed to set the hostname to hostname1.me.com (hostname1):'
+            ' OOPS on: hostname1.me.com',
+            str(ctx_mgr.exception))
+
 # vi: ts=4 expandtab