Make charm accessible and introspectable

By default, expose this charm as a LoadBalancer service to allow
external access from outside of K8S which is its principle use
case.

Add action to allow introspection of the deployed service for
the URL to connect to the Southbound DB relay.

Change-Id: Ie234ca70d9090be463b5c971a8f01302958c91f5

actions.yaml

@@ -1,2 +1,2 @@
-# NOTE: no actions yet!
-{ }
+get-southbound-db-url:
+  description: Southbound DB Connection URL for access to OVN via the relay.

src/charm.py

@@ -25,7 +25,9 @@ develop a new k8s charm using the Operator Framework:
 """
 
 import logging
-from typing import List, Mapping
+
+from ipaddress import IPv4Address, IPv6Address
+from typing import List, Mapping, Union
 
 from ops.framework import StoredState
 from ops.main import main
@@ -87,8 +89,27 @@ class OVNRelayOperatorCharm(ovn_charm.OSBaseOVNOperatorCharm):
             self,
             [
                 ('southbound', 6642),
-            ]
+            ],
+            service_type="LoadBalancer"
         )
+        self.framework.observe(
+            self.on.get_southbound_db_url_action,
+            self._get_southbound_db_url_action
+        )
+
+    def _get_southbound_db_url_action(self, event):
+        event.set_results({"url": self.southbound_db_url})
+
+    @property
+    def ingress_address(self) -> Union[IPv4Address, IPv6Address]:
+        """Network IP address for access to the OVN relay service."""
+        return self.model.get_binding(
+            'ovsdb-cms-relay').network.ingress_addresses[0]
+
+    @property
+    def southbound_db_url(self) -> str:
+        """Full connection URL for Southbound DB relay."""
+        return f"ssl:{self.ingress_address}:6442"
 
     def get_pebble_handlers(self):
         pebble_handlers = [

tests/actions.yaml

@@ -0,0 +1 @@
+../actions.yaml

tests/unit/test_ovn_relay_charm.py

@@ -63,3 +63,9 @@ class TestOVNRelayXenaOperatorCharm(test_utils.CharmTestCase):
             '/root/ovn-relay-wrapper.sh']
         for f in ovsdb_config_files:
             self.check_file('ovsdb-server', f)
+
+    def test_southbound_db_url(self):
+        self.assertEqual(
+            'ssl:10.0.0.10:6442',
+            self.harness.charm.southbound_db_url
+        )