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, 69 insertions, 1 deletions

diff --git a/cloudinit/sources/tests/test_init.py b/cloudinit/sources/tests/test_init.py
index af151154..5065083c 100644
--- a/cloudinit/sources/tests/test_init.py
+++ b/cloudinit/sources/tests/test_init.py
@@ -7,7 +7,7 @@ import stat
 from cloudinit.helpers import Paths
 from cloudinit.sources import (
     INSTANCE_JSON_FILE, DataSource)
-from cloudinit.tests.helpers import CiTestCase, skipIf
+from cloudinit.tests.helpers import CiTestCase, skipIf, mock
 from cloudinit.user_data import UserDataProcessor
 from cloudinit import util
 
@@ -108,6 +108,74 @@ class TestDataSource(CiTestCase):
         self.assertEqual('userdata_raw', datasource.userdata_raw)
         self.assertEqual('vendordata_raw', datasource.vendordata_raw)
 
+    def test_get_hostname_strips_local_hostname_without_domain(self):
+        """Datasource.get_hostname strips metadata local-hostname of domain."""
+        tmp = self.tmp_dir()
+        datasource = DataSourceTestSubclassNet(
+            self.sys_cfg, self.distro, Paths({'run_dir': tmp}))
+        self.assertTrue(datasource.get_data())
+        self.assertEqual(
+            'test-subclass-hostname', datasource.metadata['local-hostname'])
+        self.assertEqual('test-subclass-hostname', datasource.get_hostname())
+        datasource.metadata['local-hostname'] = 'hostname.my.domain.com'
+        self.assertEqual('hostname', datasource.get_hostname())
+
+    def test_get_hostname_with_fqdn_returns_local_hostname_with_domain(self):
+        """Datasource.get_hostname with fqdn set gets qualified hostname."""
+        tmp = self.tmp_dir()
+        datasource = DataSourceTestSubclassNet(
+            self.sys_cfg, self.distro, Paths({'run_dir': tmp}))
+        self.assertTrue(datasource.get_data())
+        datasource.metadata['local-hostname'] = 'hostname.my.domain.com'
+        self.assertEqual(
+            'hostname.my.domain.com', datasource.get_hostname(fqdn=True))
+
+    def test_get_hostname_without_metadata_uses_system_hostname(self):
+        """Datasource.gethostname runs util.get_hostname when no metadata."""
+        tmp = self.tmp_dir()
+        datasource = DataSourceTestSubclassNet(
+            self.sys_cfg, self.distro, Paths({'run_dir': tmp}))
+        self.assertEqual({}, datasource.metadata)
+        mock_fqdn = 'cloudinit.sources.util.get_fqdn_from_hosts'
+        with mock.patch('cloudinit.sources.util.get_hostname') as m_gethost:
+            with mock.patch(mock_fqdn) as m_fqdn:
+                m_gethost.return_value = 'systemhostname.domain.com'
+                m_fqdn.return_value = None  # No maching fqdn in /etc/hosts
+                self.assertEqual('systemhostname', datasource.get_hostname())
+                self.assertEqual(
+                    'systemhostname.domain.com',
+                    datasource.get_hostname(fqdn=True))
+
+    def test_get_hostname_without_metadata_returns_none(self):
+        """Datasource.gethostname returns None when metadata_only and no MD."""
+        tmp = self.tmp_dir()
+        datasource = DataSourceTestSubclassNet(
+            self.sys_cfg, self.distro, Paths({'run_dir': tmp}))
+        self.assertEqual({}, datasource.metadata)
+        mock_fqdn = 'cloudinit.sources.util.get_fqdn_from_hosts'
+        with mock.patch('cloudinit.sources.util.get_hostname') as m_gethost:
+            with mock.patch(mock_fqdn) as m_fqdn:
+                self.assertIsNone(datasource.get_hostname(metadata_only=True))
+                self.assertIsNone(
+                    datasource.get_hostname(fqdn=True, metadata_only=True))
+        self.assertEqual([], m_gethost.call_args_list)
+        self.assertEqual([], m_fqdn.call_args_list)
+
+    def test_get_hostname_without_metadata_prefers_etc_hosts(self):
+        """Datasource.gethostname prefers /etc/hosts to util.get_hostname."""
+        tmp = self.tmp_dir()
+        datasource = DataSourceTestSubclassNet(
+            self.sys_cfg, self.distro, Paths({'run_dir': tmp}))
+        self.assertEqual({}, datasource.metadata)
+        mock_fqdn = 'cloudinit.sources.util.get_fqdn_from_hosts'
+        with mock.patch('cloudinit.sources.util.get_hostname') as m_gethost:
+            with mock.patch(mock_fqdn) as m_fqdn:
+                m_gethost.return_value = 'systemhostname.domain.com'
+                m_fqdn.return_value = 'fqdnhostname.domain.com'
+                self.assertEqual('fqdnhostname', datasource.get_hostname())
+                self.assertEqual('fqdnhostname.domain.com',
+                                 datasource.get_hostname(fqdn=True))
+
     def test_get_data_write_json_instance_data(self):
         """get_data writes INSTANCE_JSON_FILE to run_dir as readonly root."""
         tmp = self.tmp_dir()