Minimum TTL value allowed is zero

According to ITEF https://tools.ietf.org/html/rfc2181#section-8
the definition of the ttl value is unsigned integer and can have a
minimum value of 0. This patch changes the minimum value of 1 to allow
for 0. Unit test have also been modified accordingly.

Closes-Bug: #1926429
Change-Id: I7876b4c1e2c800b654ca750211ee2e58f3ea4309
(cherry picked from commit 6ac659d241)

designate/objects/zone.py

@@ -31,7 +31,7 @@ class Zone(base.DesignateObject, base.DictObjectMixin,
         'tenant_id': fields.StringFields(nullable=True, read_only=False),
         'name': fields.DomainField(maxLength=255),
         'email': fields.EmailField(maxLength=255, nullable=True),
-        'ttl': fields.IntegerFields(nullable=True, minimum=1,
+        'ttl': fields.IntegerFields(nullable=True, minimum=0,
                                     maximum=2147483647),
         'refresh': fields.IntegerFields(nullable=True, minimum=0,
                                         maximum=2147483647, read_only=False),

designate/tests/test_api/test_v2/test_zones.py

@@ -139,8 +139,8 @@ class ApiV2ZonesTest(ApiV2TestCase):
         fixture = self.get_zone_fixture(fixture=0)
         fixture['ttl'] = 0
         body = fixture
-        self._assert_exception('invalid_object', 400, self.client.post_json,
-                               '/zones', body)
+        response = self.client.post_json('/zones', body)
+        self.assertEqual(202, response.status_int)
 
     def test_create_zone_ttl_is_greater_than_max(self):
         fixture = self.get_zone_fixture(fixture=0)

designate/tests/test_central/test_service.py

@@ -715,18 +715,18 @@ class CentralServiceTest(CentralTestCase):
         self.policy({'use_low_ttl': '!'})
         self.config(min_ttl=100,
                     group='service:central')
-        context = self.get_context()
+        context = self.get_context(project_id=1)
 
         values = self.get_zone_fixture(fixture=1)
-        values['ttl'] = 0
+        values['ttl'] = 5
 
-        with testtools.ExpectedException(ValueError):
+        with testtools.ExpectedException(exceptions.InvalidTTL):
             self.central_service.create_zone(
                 context, objects.Zone.from_dict(values))
 
     def test_create_zone_below_zero_ttl(self):
         self.policy({'use_low_ttl': '!'})
-        self.config(min_ttl=1,
+        self.config(min_ttl=0,
                     group='service:central')
         context = self.get_context()
 

releasenotes/notes/bug-1926429-allow-ttl-min-of-zero-688f7c2cf095d89d.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Allows for a minimum TTL value of zero to be used instead of 1. As stated
+    in RFC https://datatracker.ietf.org/doc/html/rfc2181#section-8.
+
+    .. _bug 1926429: https://bugs.launchpad.net/designate/+bug/1926429
+