Reorder name normalization for DNS

Having the truncation step as the last one meant we could truncate to
a trailing hyphen. This could potential cause a failure for an invalid
name. This commit reorders the normalization to put the truncation as
the first step which should avoid that problem.

Change-Id: I2219f6c73d882efc787127f02fda937f3e3b44eb
Closes-Bug: #1545153

nova/tests/unit/test_utils.py

@@ -127,6 +127,14 @@ class GenericUtilsTestCase(test.NoDBTestCase):
         hostname = "a" * 64
         self.assertEqual(63, len(utils.sanitize_hostname(hostname)))
 
+    def test_hostname_truncated_no_hyphen(self):
+        hostname = "a" * 62
+        hostname = hostname + '-' + 'a'
+        res = utils.sanitize_hostname(hostname)
+        # we trim to 63 and then trim the trailing dash
+        self.assertEqual(62, len(res))
+        self.assertFalse(res.endswith('-'), 'The hostname ends with a -')
+
     def test_generate_password(self):
         password = utils.generate_password()
         self.assertTrue([c for c in password if c in '0123456789'])

nova/utils.py

@@ -802,6 +802,7 @@ def sanitize_hostname(hostname, default_name=None):
         if six.PY3:
             hostname = hostname.decode('latin-1')
 
+    hostname = truncate_hostname(hostname)
     hostname = re.sub('[ _]', '-', hostname)
     hostname = re.sub('[^\w.-]+', '', hostname)
     hostname = hostname.lower()
@@ -810,8 +811,7 @@ def sanitize_hostname(hostname, default_name=None):
     # empty hostname
     if hostname == "" and default_name is not None:
         return truncate_hostname(default_name)
-
-    return truncate_hostname(hostname)
+    return hostname
 
 
 @contextlib.contextmanager