Add a catalogue endpoint

charmcraft.yaml

@@ -101,6 +101,11 @@ requires:
     interface: grafana_datasource_exchange
     description: |
       Integration to share with other COS components this charm's datasources, and receive theirs.
+  catalogue:
+    interface: catalogue
+    description: |
+      Integration to help users discover Tempo's memberlist UI, providing visibility into Tempo's cluster members and their health status.
+
 
 storage:
   data:
@@ -129,8 +134,8 @@ bases:
 parts:
   charm:
     # uncomment this if you add git+ dependencies in requirements.txt:
-    #build-packages:
-    #  - "git"
+    build-packages:
+    - "git"
     charm-binary-python-packages:
       - "pydantic>=2"
       - "cryptography"

lib/charms/catalogue_k8s/v1/catalogue.py

@@ -0,0 +1,164 @@
+# Copyright 2021 Canonical Ltd.
+# See LICENSE file for licensing details.
+
+"""Charm for providing services catalogues to bundles or sets of charms."""
+
+import ipaddress
+import logging
+import socket
+from typing import Optional
+
+from ops.charm import CharmBase
+from ops.framework import EventBase, EventSource, Object, ObjectEvents
+
+LIBID = "fa28b361293b46668bcd1f209ada6983"
+LIBAPI = 1
+LIBPATCH = 0
+
+DEFAULT_RELATION_NAME = "catalogue"
+
+logger = logging.getLogger(__name__)
+
+
+class CatalogueItem:
+    """`CatalogueItem` represents an application entry sent to a catalogue.
+
+    The icon is an iconify mdi string; see https://icon-sets.iconify.design/mdi.
+    """
+
+    def __init__(self, name: str, url: str, icon: str, description: str = ""):
+        self.name = name
+        self.url = url
+        self.icon = icon
+        self.description = description
+
+
+class CatalogueConsumer(Object):
+    """`CatalogueConsumer` is used to send over a `CatalogueItem`."""
+
+    def __init__(
+        self,
+        charm,
+        relation_name: str = DEFAULT_RELATION_NAME,
+        item: Optional[CatalogueItem] = None,
+    ):
+        super().__init__(charm, relation_name)
+        self._charm = charm
+        self._relation_name = relation_name
+        self._item = item
+
+        events = self._charm.on[self._relation_name]
+        self.framework.observe(events.relation_joined, self._on_relation_changed)
+        self.framework.observe(events.relation_broken, self._on_relation_changed)
+        self.framework.observe(events.relation_changed, self._on_relation_changed)
+        self.framework.observe(events.relation_departed, self._on_relation_changed)
+        self.framework.observe(events.relation_created, self._on_relation_changed)
+
+    def _on_relation_changed(self, _):
+        self._update_relation_data()
+
+    def _update_relation_data(self):
+        if not self._charm.unit.is_leader():
+            return
+
+        if not self._item:
+            return
+
+        for relation in self._charm.model.relations[self._relation_name]:
+            relation.data[self._charm.model.app]["name"] = self._item.name
+            relation.data[self._charm.model.app]["description"] = self._item.description
+            relation.data[self._charm.model.app]["url"] = self.unit_address(relation)
+            relation.data[self._charm.model.app]["icon"] = self._item.icon
+
+    def update_item(self, item: CatalogueItem):
+        """Update the catalogue item."""
+        self._item = item
+        self._update_relation_data()
+
+    def unit_address(self, relation):
+        """The unit address of the consumer, on which it is reachable.
+
+        Requires ingress to be connected for it to be routable.
+        """
+        if self._item and self._item.url:
+            return self._item.url
+
+        unit_ip = str(self._charm.model.get_binding(relation).network.bind_address)
+        if self._is_valid_unit_address(unit_ip):
+            return unit_ip
+
+        return socket.getfqdn()
+
+    def _is_valid_unit_address(self, address: str) -> bool:
+        """Validate a unit address.
+
+        At present only IP address validation is supported, but
+        this may be extended to DNS addresses also, as needed.
+
+        Args:
+            address: a string representing a unit address
+        """
+        try:
+            _ = ipaddress.ip_address(address)
+        except ValueError:
+            return False
+
+        return True
+
+
+class CatalogueItemsChangedEvent(EventBase):
+    """Event emitted when the catalogue entries change."""
+
+    def __init__(self, handle, items):
+        super().__init__(handle)
+        self.items = items
+
+    def snapshot(self):
+        """Save catalogue entries information."""
+        return {"items": self.items}
+
+    def restore(self, snapshot):
+        """Restore catalogue entries information."""
+        self.items = snapshot["items"]
+
+
+class CatalogueEvents(ObjectEvents):
+    """Events raised by `CatalogueConsumer`."""
+
+    items_changed = EventSource(CatalogueItemsChangedEvent)
+
+
+class CatalogueProvider(Object):
+    """`CatalogueProvider` is the side of the relation that serves the actual service catalogue."""
+
+    on = CatalogueEvents()  # pyright: ignore
+
+    def __init__(self, charm: CharmBase, relation_name: str = DEFAULT_RELATION_NAME):
+        super().__init__(charm, relation_name)
+        self._charm = charm
+        self._relation_name = relation_name
+        events = self._charm.on[self._relation_name]
+        self.framework.observe(events.relation_changed, self._on_relation_changed)
+        self.framework.observe(events.relation_joined, self._on_relation_changed)
+        self.framework.observe(events.relation_departed, self._on_relation_changed)
+        self.framework.observe(events.relation_broken, self._on_relation_broken)
+
+    def _on_relation_broken(self, event):
+        self.on.items_changed.emit(items=self.items)  # pyright: ignore
+
+    def _on_relation_changed(self, event):
+        self.on.items_changed.emit(items=self.items)  # pyright: ignore
+
+    @property
+    def items(self):
+        """A list of apps sent over relation data."""
+        return [
+            {
+                "name": relation.data[relation.app].get("name", ""),
+                "url": relation.data[relation.app].get("url", ""),
+                "icon": relation.data[relation.app].get("icon", ""),
+                "description": relation.data[relation.app].get("description", ""),
+            }
+            for relation in self._charm.model.relations[self._relation_name]
+            if relation.app and relation.units
+        ]

requirements.txt

@@ -5,7 +5,8 @@ lightkube>=0.15.4
 lightkube-models>=1.24.1.4
 tenacity==8.2.3
 pydantic>=2
-cosl>=0.0.46
+# FIXME: when cos-lib PR is merged
+cosl@git+https://github.com/canonical/cos-lib@TAP-158
 
 # crossplane is a package from nginxinc to interact with the Nginx config
 crossplane

src/charm.py

@@ -12,6 +12,7 @@
 from typing import Any, Dict, List, Optional, Set, Tuple, cast, get_args
 
 import ops
+from charms.catalogue_k8s.v1.catalogue import CatalogueItem
 from charms.grafana_k8s.v0.grafana_source import GrafanaSourceProvider
 from charms.prometheus_k8s.v1.prometheus_remote_write import (
     PrometheusRemoteWriteConsumer,
@@ -113,6 +114,7 @@ def __init__(self, *args):
                 "workload-tracing": "self-workload-tracing",
                 "send-datasource": None,
                 "receive-datasource": "receive-datasource",
+                "catalogue": "catalogue",
             },
             nginx_config=NginxConfig(server_name=self.hostname).config,
             workers_config=self.tempo.config,
@@ -121,6 +123,7 @@ def __init__(self, *args):
             remote_write_endpoints=self.remote_write_endpoints,  # type: ignore
             # TODO: future Tempo releases would be using otlp_xx protocols instead.
             workload_tracing_protocols=["jaeger_thrift_http"],
+            catalogue_item=self._catalogue_item,
         )
 
         # configure this tempo as a datasource in grafana
@@ -234,6 +237,23 @@ def enabled_receivers(self) -> Set[str]:
         )
         return enabled_receivers
 
+    @property
+    def _catalogue_item(self) -> CatalogueItem:
+        """A catalogue application entry for this Tempo instance."""
+        return CatalogueItem(
+            # use app.name in case there are multiple Tempo applications deployed.
+            name=self.app.name,
+            icon="transit-connection-variant",
+            # Unlike Prometheus, Tempo doesn't have a sophisticated web UI.
+            # Instead, we'll show the current cluster members and their health status.
+            # ref: https://grafana.com/docs/tempo/latest/api_docs/
+            url=f"{self._external_url}:3200/memberlist",
+            description=(
+                "Tempo is a distributed tracing backend by Grafana, supporting Jaeger, "
+                "Zipkin, and OpenTelemetry protocols."
+            ),
+        )
+
     ##################
     # EVENT HANDLERS #
     ##################

tests/scenario/conftest.py

@@ -22,9 +22,14 @@ def patch_buffer_file_for_charm_tracing(tmp_path):
 
 @pytest.fixture(autouse=True, scope="session")
 def cleanup_prometheus_alert_rules():
-    # some tests trigger the charm to generate prometheus alert rules file in ./src; clean it up
+    # some tests trigger the charm to generate prometheus alert rules file in src/prometheus_alert_rules/consolidated_rules; clean it up
     yield
-    src_path = Path(__file__).parent / "src"
+    src_path = (
+        Path(__file__).parent.parent.parent
+        / "src"
+        / "prometheus_alert_rules"
+        / "consolidated_rules"
+    )
     rmtree(src_path)