Introduce show-proxied-endpoints action

* Introduce the 'show-proxied-endpoints' action to expose the URLs
  provided by the applications related with traefik-k8s via the ingress
  and ingress-per-unit relation interfaces
* Updated the ingress library to expose on the Provider side which URLs
  are provided to which applications
* Updated the ingress_per_unit library to expose on the Provider side which URLs
  are provided to which units

actions.yaml

@@ -0,0 +1,3 @@
+show-proxied-endpoints:
+  description: |
+    Returns a list of endpoints proxied by this Traefik proxy.

lib/charms/traefik_k8s/v0/ingress.py

@@ -61,7 +61,7 @@ def _handle_ingress(self, event):
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 1
+LIBPATCH = 2
 
 log = logging.getLogger(__name__)
 
@@ -163,6 +163,29 @@ def is_failed(self, relation: Relation = None):
             raise RelationDataMismatchError(relation, other_app)
         return False
 
+    @property
+    def proxied_endpoints(self):
+        """Returns the ingress settings provided to applications by this IngressPerAppProvider.
+
+        For example, when this IngressPerAppProvider has provided the
+        `http://foo.bar/my-model.my-app` URL to the my-app application, the returned dictionary
+        will be:
+
+        ```
+        {
+            "my-app": {
+                "url": "http://foo.bar/my-model.my-app"
+            }
+        }
+        ```
+        """
+        return {
+            ingress_relation.app.name: self.unwrap(ingress_relation)[self.charm.app].get(
+                "ingress", {}
+            )
+            for ingress_relation in self.charm.model.relations[self.endpoint]
+        }
+
 
 class IngressPerAppRequest:
     """A request for per-application ingress."""

lib/charms/traefik_k8s/v0/ingress_per_unit.py

@@ -68,7 +68,7 @@ def _handle_ingress_per_unit(self, event):
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 2
+LIBPATCH = 3
 
 log = logging.getLogger(__name__)
 
@@ -169,6 +169,32 @@ def is_failed(self, relation: Relation = None):
                 raise RelationDataMismatchError(relation, unit)
         return False
 
+    @property
+    def proxied_endpoints(self):
+        """Returns the ingress settings provided to units by this IngressPerUnitProvider.
+
+        For example, when this IngressPerUnitProvider has provided the
+        `http://foo.bar/my-model.my-app-1` and `http://foo.bar/my-model.my-app-2` URLs to
+        the two units of the my-app application, the returned dictionary will be:
+
+        ```
+        {
+            "my-app/1": {
+                "url": "http://foo.bar/my-model.my-app-1"
+            },
+            "my-app/2": {
+                "url": "http://foo.bar/my-model.my-app-2"
+            }
+        }
+        ```
+        """
+        results = {}
+
+        for ingress_relation in self.charm.model.relations[self.endpoint]:
+            results.update(self.unwrap(ingress_relation)[self.charm.app].get("ingress", {}))
+
+        return results
+
 
 class IngressRequest:
     """A request for per-unit ingress."""

src/charm.py

@@ -5,6 +5,7 @@
 """Charm Traefik."""
 
 import enum
+import json
 import logging
 from typing import Optional, Tuple
 
@@ -16,6 +17,7 @@
 from lightkube import Client
 from lightkube.resources.core_v1 import Service
 from ops.charm import (
+    ActionEvent,
     CharmBase,
     ConfigChangedEvent,
     PebbleReadyEvent,
@@ -99,6 +101,22 @@ def __init__(self, *args):
         self.framework.observe(self.ingress_per_unit.on.failed, self._handle_ingress_failure)
         self.framework.observe(self.ingress_per_unit.on.broken, self._handle_ingress_broken)
 
+        # Action handlers
+        self.framework.observe(
+            self.on.show_proxied_endpoints_action, self._on_show_proxied_endpoints
+        )
+
+    def _on_show_proxied_endpoints(self, event: ActionEvent):
+        try:
+            result = {}
+            result.update(self.ingress_per_unit.proxied_endpoints)
+            result.update(self.ingress_per_app.proxied_endpoints)
+
+            event.set_results({"proxied-endpoints": json.dumps(result)})
+        except Exception as e:
+            logger.exception("Action 'show-proxied-endpoints' failed")
+            event.fail(str(e))
+
     def _on_traefik_pebble_ready(self, _: PebbleReadyEvent):
         # The the Traefik container comes up, e.g., after a pod churn, we
         # ignore the unit status and start fresh.

tests/unit/test_charm.py

@@ -1,10 +1,12 @@
 # Copyright 2022 Canonical Ltd.
 # See LICENSE file for licensing details.
 
+import json
 import unittest
-from unittest.mock import patch
+from unittest.mock import Mock, patch
 
 import yaml
+from ops.charm import ActionEvent
 from ops.model import ActiveStatus, BlockedStatus, WaitingStatus
 from ops.testing import Harness
 from test_lib_helpers import MockIPARequirer, MockIPURequirer
@@ -373,3 +375,62 @@ def test_relation_broken(self):
             raise Exception("The line above should fail")
         except FileNotFoundError:
             pass
+
+    @patch("charm._get_loadbalancer_status", lambda **unused: None)
+    @patch("charm.KubernetesServicePatch", lambda **unused: None)
+    def test_show_proxied_endpoints_action_no_relations(self):
+        self.harness.begin_with_initial_hooks()
+
+        action_event = Mock(spec=ActionEvent)
+        self.harness.charm._on_show_proxied_endpoints(action_event)
+        action_event.set_results.assert_called_once_with({"proxied-endpoints": "{}"})
+
+    @patch("charm._get_loadbalancer_status", lambda **unused: None)
+    @patch("charm.KubernetesServicePatch", lambda **unused: None)
+    def test_show_proxied_endpoints_action_only_ingress_per_app_relations(self):
+        self.harness.set_leader(True)
+        self.harness.update_config({"external_hostname": "testhostname"})
+        self.harness.begin_with_initial_hooks()
+
+        requirer = MockIPARequirer(self.harness)
+        requirer.relate()
+        requirer.request(host="10.0.0.1", port=3000)
+
+        self.harness.container_pebble_ready("traefik")
+
+        action_event = Mock(spec=ActionEvent)
+        self.harness.charm._on_show_proxied_endpoints(action_event)
+        action_event.set_results.assert_called_once_with(
+            {
+                "proxied-endpoints": json.dumps(
+                    {"ingress-remote": {"url": "http://testhostname:80/test-model-ingress-remote"}}
+                )
+            }
+        )
+
+    @patch("charm._get_loadbalancer_status", lambda **unused: None)
+    @patch("charm.KubernetesServicePatch", lambda **unused: None)
+    def test_show_proxied_endpoints_action_only_ingress_per_unit_relations(self):
+        self.harness.set_leader(True)
+        self.harness.update_config({"external_hostname": "testhostname"})
+        self.harness.begin_with_initial_hooks()
+
+        requirer = MockIPURequirer(self.harness)
+        requirer.relate()
+        requirer.request(host="10.0.0.1", port=3000)
+
+        self.harness.container_pebble_ready("traefik")
+
+        action_event = Mock(spec=ActionEvent)
+        self.harness.charm._on_show_proxied_endpoints(action_event)
+        action_event.set_results.assert_called_once_with(
+            {
+                "proxied-endpoints": json.dumps(
+                    {
+                        "ingress-per-unit-remote/0": {
+                            "url": "http://testhostname:80/test-model-ingress-per-unit-remote-0"
+                        }
+                    }
+                )
+            }
+        )