Add support for 'availability_zone' parameter.

I've added support for 'availability_zone' parameter. I've added
'dhcp_agent.ini' template and implemented the parameter to be consumed
via 'neutron-plugin' relation settings.

Change-Id: I015a6dfcf89800043bd7dbf02b07da07d8a7d728
Closes-Bug: 1595937

hooks/neutron_ovs_context.py

@@ -114,6 +114,32 @@ class OVSPluginContext(context.NeutronContext):
         return ovs_ctxt
 
 
+class DHCPAgentContext(OSContextGenerator):
+
+    def __call__(self):
+        """Return the 'default_availability_zone' from the principal that this
+        ovs unit is attached to (as a subordinate).
+
+        :returns: {} if no relation set, or
+            {'availability_zone': availability_zone from principal relation}
+        """
+        # as ovs is a subordinate charm, it should only have one relation to
+        # its principal charm.  Thus we can take the 1st (only) element in each
+        # list.
+        rids = relation_ids('neutron-plugin')
+        if rids:
+            rid = rids[0]
+            units = related_units(rid)
+            if units:
+                availability_zone = relation_get(
+                    'default_availability_zone',
+                    rid=rid,
+                    unit=units[0])
+                if availability_zone:
+                    return {'availability_zone': availability_zone}
+        return {}
+
+
 class L3AgentContext(OSContextGenerator):
 
     def __call__(self):

hooks/neutron_ovs_utils.py

@@ -178,7 +178,7 @@ METADATA_RESOURCE_MAP = OrderedDict([
 DHCP_RESOURCE_MAP = OrderedDict([
     (NEUTRON_DHCP_AGENT_CONF, {
         'services': ['neutron-dhcp-agent'],
-        'contexts': [],
+        'contexts': [neutron_ovs_context.DHCPAgentContext()],
     }),
 ])
 DVR_RESOURCE_MAP = OrderedDict([

templates/mitaka/dhcp_agent.ini

@@ -0,0 +1,22 @@
+# mitaka
+###############################################################################
+# [ WARNING ]
+# Configuration file maintained by Juju. Local changes may be overwritten.
+# 
+###############################################################################
+
+[DEFAULT]
+state_path = /var/lib/neutron
+interface_driver = neutron.agent.linux.interface.OVSInterfaceDriver
+dhcp_driver = neutron.agent.linux.dhcp.Dnsmasq
+root_helper = sudo /usr/bin/neutron-rootwrap /etc/neutron/rootwrap.conf
+
+enable_metadata_network = True
+enable_isolated_metadata = True
+
+ovs_use_veth = True
+
+[AGENT]
+{% if availability_zone -%}
+availability_zone = {{ availability_zone }}
+{% endif -%}

unit_tests/test_neutron_ovs_context.py

@@ -234,6 +234,44 @@ class OVSPluginContextTest(CharmTestCase):
         self.assertEquals(expect, napi_ctxt())
 
 
+class DHCPAgentContextTest(CharmTestCase):
+
+    def setUp(self):
+        super(DHCPAgentContextTest, self).setUp(context, TO_PATCH)
+        self.config.side_effect = self.test_config.get
+
+    def tearDown(self):
+        super(DHCPAgentContextTest, self).tearDown()
+
+    def test_default_availability_zone_not_provided(self):
+        self.relation_ids.return_value = ['rid1']
+        self.related_units.return_value = ['nova-compute/0']
+        self.relation_get.return_value = None
+        self.assertEqual(
+            context.DHCPAgentContext()(),
+            {}
+        )
+        self.relation_ids.assert_called_with('neutron-plugin')
+        self.relation_get.assert_called_once_with(
+            'default_availability_zone',
+            rid='rid1',
+            unit='nova-compute/0')
+
+    def test_default_availability_zone_provided(self):
+        self.relation_ids.return_value = ['rid1']
+        self.related_units.return_value = ['nova-compute/0']
+        self.relation_get.return_value = 'nova'
+        self.assertEqual(
+            context.DHCPAgentContext()(),
+            {'availability_zone': 'nova'}
+        )
+        self.relation_ids.assert_called_with('neutron-plugin')
+        self.relation_get.assert_called_once_with(
+            'default_availability_zone',
+            rid='rid1',
+            unit='nova-compute/0')
+
+
 class L3AgentContextTest(CharmTestCase):
 
     def setUp(self):