Use hosts official name for FQDN

The current implementations use of a specific interface to build
FQDN from has the undesired side effect of the ``nova-compute`` and
``neutron-openvswitch`` charms ending up with using different
hostnames in some situations.  It may also lead to use of a
identifier that is mutable throughout the lifetime of a deployment.

Use of a specific interface was chosen due to ``socket.getfqdn()``
not giving reliable results (https://bugs.python.org/issue5004).

This patch gets the FQDN by mimickingthe behaviour of a call to
``hostname -f`` with fallback to shortname on failure.

Add relevant update from c-h.

Needed-By: Ic8f8742261b773484687985aa0a366391cd2737a
Change-Id: I82db81937e5a46dc6bd222b7160ca1fa5b190c10
Closes-Bug: #1839300

hooks/charmhelpers/contrib/openstack/context.py

@@ -2177,9 +2177,66 @@ class LogrotateContext(OSContextGenerator):
 class HostInfoContext(OSContextGenerator):
     """Context to provide host information."""
 
+    def __init__(self, use_fqdn_hint_cb=None):
+        """Initialize HostInfoContext
+
+        :param use_fqdn_hint_cb: Callback whose return value used to populate
+                                 `use_fqdn_hint`
+        :type use_fqdn_hint_cb: Callable[[], bool]
+        """
+        # Store callback used to get hint for whether FQDN should be used
+
+        # Depending on the workload a charm manages, the use of FQDN vs.
+        # shortname may be a deploy-time decision, i.e. behaviour can not
+        # change on charm upgrade or post-deployment configuration change.
+
+        # The hint is passed on as a flag in the context to allow the decision
+        # to be made in the Jinja2 configuration template.
+        self.use_fqdn_hint_cb = use_fqdn_hint_cb
+
+    def _get_canonical_name(self, name=None):
+        """Get the official FQDN of the host
+
+        The implementation of ``socket.getfqdn()`` in the standard Python
+        library does not exhaust all methods of getting the official name
+        of a host ref Python issue https://bugs.python.org/issue5004
+
+        This function mimics the behaviour of a call to ``hostname -f`` to
+        get the official FQDN but returns an empty string if it is
+        unsuccessful.
+
+        :param name: Shortname to get FQDN on
+        :type name: Optional[str]
+        :returns: The official FQDN for host or empty string ('')
+        :rtype: str
+        """
+        name = name or socket.gethostname()
+        fqdn = ''
+
+        if six.PY2:
+            exc = socket.error
+        else:
+            exc = OSError
+
+        try:
+            addrs = socket.getaddrinfo(
+                name, None, 0, socket.SOCK_DGRAM, 0, socket.AI_CANONNAME)
+        except exc:
+            pass
+        else:
+            for addr in addrs:
+                if addr[3]:
+                    if '.' in addr[3]:
+                        fqdn = addr[3]
+                    break
+        return fqdn
+
     def __call__(self):
+        name = socket.gethostname()
         ctxt = {
-            'host_fqdn': socket.getfqdn(),
-            'host': socket.gethostname(),
+            'host_fqdn': self._get_canonical_name(name) or name,
+            'host': name,
+            'use_fqdn_hint': (
+                self.use_fqdn_hint_cb() if self.use_fqdn_hint_cb else False)
         }
         return ctxt

hooks/nova_compute_context.py

@@ -16,7 +16,6 @@ import json
 import os
 import platform
 import shutil
-import socket
 import uuid
 
 from charmhelpers.core.unitdata import kv
@@ -795,23 +794,6 @@ class HostIPContext(context.OSContextGenerator):
             # NOTE: do not format this even for ipv6 (see bug 1499656)
             ctxt['host_ip'] = host_ip
 
-            # the contents of the Nova ``host`` configuration option is
-            # referenced throughout a OpenStack deployment, an example being
-            # Neutron port bindings.  It's value should not change after a
-            # individual units initial deployment.
-            #
-            # We do want to migrate to using FQDNs so we enable this for new
-            # installations.
-            db = kv()
-            if db.get('nova-compute-charm-use-fqdn', False):
-                fqdn = socket.getfqdn(host_ip)
-                if '.' in fqdn:
-                    # only populate the value if getfqdn() is able to find an
-                    # actual FQDN for this host.  If not, we revert back to
-                    # not setting the configuration option and use Nova's
-                    # default behaviour.
-                    ctxt['host'] = fqdn
-
         return ctxt
 
 

hooks/nova_compute_hooks.py

@@ -117,6 +117,7 @@ from nova_compute_utils import (
     get_availability_zone,
     remove_old_packages,
     MULTIPATH_PACKAGES,
+    USE_FQDN_KEY,
 )
 
 from charmhelpers.contrib.network.ip import (
@@ -163,7 +164,7 @@ def install():
     release = os_release('nova-common')
     if CompareOpenStackReleases(release) >= 'stein':
         db = kv()
-        db.set('nova-compute-charm-use-fqdn', True)
+        db.set(USE_FQDN_KEY, True)
         db.flush()
 
     install_vaultlocker()

hooks/nova_compute_utils.py

@@ -180,6 +180,19 @@ NOVA_NETWORK_AA_PROFILE_PATH = ('/etc/apparmor.d/{}'
 
 LIBVIRT_TYPES = ['kvm', 'qemu', 'lxc']
 
+USE_FQDN_KEY = 'nova-compute-charm-use-fqdn'
+
+
+def use_fqdn_hint():
+    """Hint for whether FQDN should be used for agent registration
+
+    :returns: True or False
+    :rtype: bool
+    """
+    db = kv()
+    return db.get(USE_FQDN_KEY, False)
+
+
 BASE_RESOURCE_MAP = {
     NOVA_CONF: {
         'services': ['nova-compute'],
@@ -213,7 +226,9 @@ BASE_RESOURCE_MAP = {
                      vaultlocker.VaultKVContext(
                          vaultlocker.VAULTLOCKER_BACKEND),
                      context.IdentityCredentialsContext(
-                         rel_name='cloud-credentials')],
+                         rel_name='cloud-credentials'),
+                     context.HostInfoContext(use_fqdn_hint_cb=use_fqdn_hint),
+                     ],
     },
     VENDORDATA_FILE: {
         'services': [],

templates/stein/nova.conf

@@ -17,8 +17,8 @@ enabled_apis=osapi_compute,metadata
 my_ip = {{ host_ip }}
 force_raw_images = {{ force_raw_images }}
 
-{% if host -%}
-host = {{ host }}
+{% if use_fqdn_hint and host_fqdn -%}
+host = {{ host_fqdn }}
 {% endif -%}
 
 {% if debug -%}

templates/train/nova.conf

@@ -20,8 +20,8 @@ enabled_apis=osapi_compute,metadata
 my_ip = {{ host_ip }}
 force_raw_images = {{ force_raw_images }}
 
-{% if host -%}
-host = {{ host }}
+{% if use_fqdn_hint and host_fqdn -%}
+host = {{ host_fqdn }}
 {% endif -%}
 
 {% if debug -%}

unit_tests/test_actions_openstack_upgrade.py

@@ -19,7 +19,8 @@ os.environ['JUJU_UNIT_NAME'] = 'nova_compute'
 
 with patch('charmhelpers.core.hookenv.config') as config:
     config.return_value = 'nova'
-    import nova_compute_utils as utils  # noqa
+    with patch('charmhelpers.contrib.openstack.context.HostInfoContext'):
+        import nova_compute_utils as utils  # noqa
 
 with patch('nova_compute_utils.restart_map'):
     with patch('nova_compute_utils.register_configs'):

unit_tests/test_nova_compute_contexts.py

@@ -656,25 +656,14 @@ class NovaComputeContextTests(CharmTestCase):
         libvirt = context.NovaComputeLibvirtContext()
         self.assertFalse('cpu-mode' in libvirt())
 
-    @patch.object(context.socket, 'getfqdn')
     @patch('subprocess.call')
-    def test_host_IP_context(self, _call, _getfqdn):
+    def test_host_IP_context(self, _call):
         self.log = fake_log
         self.get_relation_ip.return_value = '172.24.0.79'
-        self.kv.return_value = FakeUnitdata()
         host_ip = context.HostIPContext()
         self.assertEqual({'host_ip': '172.24.0.79'}, host_ip())
         self.get_relation_ip.assert_called_with('cloud-compute',
                                                 cidr_network=None)
-        self.kv.return_value = FakeUnitdata(
-            **{'nova-compute-charm-use-fqdn': True})
-        _getfqdn.return_value = 'some'
-        host_ip = context.HostIPContext()
-        self.assertEqual({'host_ip': '172.24.0.79'}, host_ip())
-        _getfqdn.return_value = 'some.hostname'
-        host_ip = context.HostIPContext()
-        self.assertDictEqual({'host': 'some.hostname',
-                              'host_ip': '172.24.0.79'}, host_ip())
 
     @patch('subprocess.call')
     def test_host_IP_context_ipv6(self, _call):

unit_tests/test_nova_compute_hooks.py

@@ -129,7 +129,7 @@ class NovaComputeRelationsTests(CharmTestCase):
         kv = MagicMock()
         _kv.return_value = kv
         hooks.install()
-        kv.set.assert_called_once_with('nova-compute-charm-use-fqdn', True)
+        kv.set.assert_called_once_with(hooks.USE_FQDN_KEY, True)
         kv.flush.assert_called_once_with()
 
     @patch.object(hooks, 'ceph_changed')

unit_tests/test_nova_compute_utils.py

@@ -1134,3 +1134,10 @@ class NovaComputeUtilsTests(CharmTestCase):
         _hook_name.return_value = "post-series-upgrade"
         self.assertEqual(_full,
                          utils.services_to_pause_or_resume())
+
+    @patch.object(utils, 'kv')
+    def test_use_fqdn_hint(self, _kv):
+        _kv().get.return_value = False
+        self.assertEquals(utils.use_fqdn_hint(), False)
+        _kv().get.return_value = True
+        self.assertEquals(utils.use_fqdn_hint(), True)