Ignore IPv6 addresses if force_ipv4 is set

Currently if a cloud config sets force_ipv4, it will still have the
public_v6 field populated if the provider API gives an IPv6 address.

I can not see why you would want this address populated if you are
telling the cloud to force IPv4.  As a concrete example;
If6e1a0402b9b7f93cc76623c01049764abc68b2a proposes in zuul-jobs adding
the IPv6 address to /etc/hosts for multinode jobs.  It does this by
walking the nodepool interface values, which on some clouds with
force_ipv4 set will have invalid/unconfigured IPv6 entries.

I've updated the documentation to expand a bit more on what situations
this flag might be useful, which AIUI is really mostly about clouds
that return you an IPv6 address in the API but don't give you a
practical way to auto-configure it.

Change-Id: I7aaaf44ab1a1d4d25225843227ef6ab6d8564063

doc/source/user/config/configuration.rst

@@ -254,18 +254,22 @@ are connecting to OpenStack can share a cache should you desire.
 IPv6
 ----
 
-IPv6 is the future, and you should always use it if your cloud supports it and
-if your local network supports it. Both of those are easily detectable and all
-friendly software should do the right thing. However, sometimes you might
-exist in a location where you have an IPv6 stack, but something evil has
-caused it to not actually function. In that case, there is a config option
-you can set to unbreak you `force_ipv4`, or `OS_FORCE_IPV4` boolean
-environment variable.
+IPv6 is the future, and you should always use it if your cloud
+supports it and if your local network supports it. Both of those are
+easily detectable and all friendly software should do the right thing.
+
+However, sometimes a cloud API may return IPv6 information that is not
+useful to a production deployment.  For example, the API may provide
+an IPv6 address for a server, but not provide that to the host
+instance via metadata (configdrive) or standard IPv6 autoconfiguration
+methods (i.e. the host either needs to make a bespoke API call, or
+otherwise statically configure itself).
+
+For such situations, you can set the ``force_ipv4``, or ``OS_FORCE_IPV4``
+boolean environment variable.  For example:
 
 .. code-block:: yaml
 
-  client:
-    force_ipv4: true
   clouds:
     mtvexx:
       profile: vexxhost
@@ -276,15 +280,24 @@ environment variable.
       region_name: ca-ymq-1
       dns_api_version: 1
     monty:
-      profile: rax
+      profile: fooprovider
+      force_ipv4: true
       auth:
         username: mordred@inaugust.com
         password: XXXXXXXXX
         project_name: mordred@inaugust.com
-      region_name: DFW
+      region_name: RegionFoo
+
+The above snippet will tell client programs to prefer the IPv4 address
+and leave the ``public_v6`` field of the `Server` object blank for the
+``fooprovider`` cloud .  You can also set this with a client flag for
+all clouds:
+
+.. code-block:: yaml
+
+  client:
+    force_ipv4: true
 
-The above snippet will tell client programs to prefer returning an IPv4
-address.
 
 Per-region settings
 -------------------

openstack/cloud/meta.py

@@ -280,6 +280,7 @@ def get_server_external_ipv6(server):
     :param server: the server from which we want to get an IPv6 address
     :return: a string containing the IPv6 address or None
     """
+    # Don't return ipv6 interfaces if forcing IPv4
     if server['accessIPv6']:
         return server['accessIPv6']
     addresses = find_nova_addresses(addresses=server['addresses'], version=6)
@@ -448,7 +449,12 @@ def add_server_interfaces(cloud, server):
     # not exist to remain consistent with the pre-existing missing values
     server['addresses'] = _get_supplemental_addresses(cloud, server)
     server['public_v4'] = get_server_external_ipv4(cloud, server) or ''
-    server['public_v6'] = get_server_external_ipv6(server) or ''
+    # If we're forcing IPv4, then don't report IPv6 interfaces which
+    # are likely to be unconfigured.
+    if cloud.force_ipv4:
+        server['public_v6'] = ''
+    else:
+        server['public_v6'] = get_server_external_ipv6(server) or ''
     server['private_v4'] = get_server_private_ip(server, cloud) or ''
     server['interface_ip'] = _get_interface_ip(cloud, server) or ''
 

openstack/tests/unit/cloud/test_meta.py

@@ -1018,6 +1018,7 @@ class TestMeta(base.TestCase):
         hostvars = meta.get_hostvars_from_server(
             fake_cloud, meta.obj_to_munch(standard_fake_server))
         self.assertEqual(PUBLIC_V4, hostvars['interface_ip'])
+        self.assertEqual('', hostvars['public_v6'])
 
     @mock.patch.object(meta, 'get_server_external_ipv4')
     def test_private_interface_ip(self, mock_get_server_external_ipv4):

releasenotes/notes/force_ipv4_no_ipv6_address-9842168b5d05d262.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    Cloud with the `force_ipv4` flag will no longer return a
+    `public_v6` value, even if one is provided by the cloud.  This is
+    to avoid having entries for unconfigured interfaces.