parse controller API port from apiaddresses in agent.conf

src/charm.py

@@ -11,7 +11,8 @@
 from ops.framework import StoredState
 from ops.charm import RelationJoinedEvent, RelationDepartedEvent
 from ops.main import main
-from ops.model import ActiveStatus, BlockedStatus, Relation
+from ops.model import ActiveStatus, BlockedStatus, ErrorStatus, Relation
+from typing import List
 
 logger = logging.getLogger(__name__)
 
@@ -79,14 +80,19 @@ def _on_metrics_endpoint_relation_created(self, event: RelationJoinedEvent):
         self.control_socket.add_metrics_user(username, password)
 
         # Set up Prometheus scrape config
+        try:
+            api_port = self.api_port()
+        except AgentConfException as e:
+            self.unit.status = ErrorStatus(f"can't read controller API port from agent.conf: {e}")
+
         metrics_endpoint = MetricsEndpointProvider(
             self,
             jobs=[{
                 "metrics_path": "/introspection/metrics",
                 "scheme": "https",
                 "static_configs": [{
                     "targets": [
-                        f'*:{self.api_port()}'
+                        f'*:{api_port}'
                     ]
                 }],
                 "basic_auth": {
@@ -116,7 +122,20 @@ def _agent_conf(self, key: str):
 
     def api_port(self) -> str:
         """Return the port on which the controller API server is listening."""
-        return self._agent_conf('apiport')
+        api_port = self._agent_conf('apiport')
+        if api_port:
+            return api_port
+
+        # If there is no 'apiport' key, try to parse 'apiaddresses'.
+        api_addresses = self._agent_conf('apiaddresses')
+        if not api_addresses:
+            raise AgentConfException("neither 'apiport' or 'apiaddresses' defined in agent.conf")
+        if isinstance(api_addresses, List) == 0:
+            raise AgentConfException("agent.conf key 'apiaddresses' is not a list")
+        if len(api_addresses) == 0:
+            raise AgentConfException("agent.conf key 'apiaddresses' is empty list")
+
+        return api_addresses[0].split(':')[1]
 
     def ca_cert(self) -> str:
         """Return the controller's CA certificate."""
@@ -136,5 +155,9 @@ def generate_password() -> str:
     return secrets.token_urlsafe(16)
 
 
+class AgentConfException(Exception):
+    """Raised when there are errors reading info from agent.conf."""
+
+
 if __name__ == "__main__":
     main(JujuControllerCharm)

tests/test_charm.py

@@ -8,7 +8,8 @@
 from unittest.mock import mock_open, patch
 
 agent_conf = '''
-apiport: 17070
+apiaddresses:
+- localhost:17070
 cacert: fake
 '''