feat: add grafana_base_url to Grafana source

lib/charms/grafana_k8s/v0/grafana_source.py

@@ -162,7 +162,7 @@ def __init__(self, *args):
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 24
+LIBPATCH = 26
 
 logger = logging.getLogger(__name__)
 
@@ -429,6 +429,27 @@ def update_source(self, source_url: Optional[str] = ""):
                 continue
             self._set_sources(rel)
 
+    def get_grafana_base_urls(self) -> Dict[str, str]:
+        # TODO update docstring
+        """Get the grafana external URL assigned by the remote end(s) to this datasource.
+
+        Returns a mapping from remote application UIDs to unit names to datasource uids.
+        """
+        urls = {}
+        for rel in self._charm.model.relations.get(self._relation_name, []):
+            if not rel:
+                continue
+            app_databag = rel.data[rel.app]
+            grafana_uid = app_databag.get("grafana_uid")
+            if not grafana_uid:
+                logger.warning(
+                    "remote end is using an old grafana_datasource interface: "
+                    "`grafana_uid` field not found."
+                )
+                continue
+            urls[grafana_uid] = app_databag.get("grafana_base_url")
+        return urls
+
     def get_source_uids(self) -> Dict[str, Dict[str, str]]:
         """Get the datasource UID(s) assigned by the remote end(s) to this datasource.
 
@@ -504,13 +525,17 @@ class GrafanaSourceConsumer(Object):
     def __init__(
         self,
         charm: CharmBase,
+        grafana_uid: str,
+        grafana_base_url: str,
         relation_name: str = DEFAULT_RELATION_NAME,
     ) -> None:
         """A Grafana based Monitoring service consumer, i.e., the charm that uses a datasource.
 
         Args:
             charm: a :class:`CharmBase` instance that manages this
                 instance of the Grafana source service.
+            grafana_uid: an unique identifier for this grafana-k8s application.
+            grafana_base_url: the base URL (potentially ingressed) for this grafana-k8s application.
             relation_name: string name of the relation that is provides the
                 Grafana source service. It is strongly advised not to change
                 the default, so that people deploying your charm will have a
@@ -524,6 +549,8 @@ def __init__(
         super().__init__(charm, relation_name)
         self._relation_name = relation_name
         self._charm = charm
+        self._grafana_uid = grafana_uid
+        self._grafana_base_url = grafana_base_url
         events = self._charm.on[relation_name]
 
         # We're stuck with this forever now so upgrades work, or until such point as we can
@@ -577,15 +604,9 @@ def _publish_source_uids(self, rel: Relation, uids: Dict[str, str]):
 
         Assumes only leader unit will call this method
         """
-        unique_grafana_name = "juju_{}_{}_{}_{}".format(
-            self._charm.model.name,
-            self._charm.model.uuid,
-            self._charm.model.app.name,
-            self._charm.model.unit.name.split("/")[1],  # type: ignore
-        )
-
-        rel.data[self._charm.app]["grafana_uid"] = unique_grafana_name
+        rel.data[self._charm.app]["grafana_uid"] = self._grafana_uid
         rel.data[self._charm.app]["datasource_uids"] = json.dumps(uids)
+        rel.data[self._charm.app]["grafana_base_url"] = self._grafana_base_url
 
     def _get_source_config(self, rel: Relation):
         """Generate configuration from data stored in relation data by providers."""

src/charm.py

@@ -11,6 +11,7 @@
 
     https://discourse.charmhub.io/t/4208
 """
+
 import datetime
 import logging
 import os
@@ -554,7 +555,13 @@ def _configure(self):  # noqa: C901
         # operations fail, better to let the charm go into error state than setting blocked.
         if self.server_cert.available and not self._certs_on_disk:
             self._update_cert()
-
+        # Obtain the Grafana base URL
+        urls = self.grafana_source_provider.get_grafana_base_urls()
+        if urls:
+            grafana_uid = next(iter(urls))  # TODO How to handle multiple grafanas?
+            grafana_external_url = urls[grafana_uid]
+        else:
+            grafana_external_url = ""
         config = ConfigBuilder(
             instance_addr=self.hostname,
             alertmanager_url=self._alerting_config(),
@@ -565,6 +572,7 @@ def _configure(self):  # noqa: C901
             http_tls=self._tls_ready,
             tsdb_versions_migration_dates=self._tsdb_versions_migration_dates,
             reporting_enabled=bool(self.config["reporting-enabled"]),
+            grafana_external_url=grafana_external_url,
         ).build()
 
         # Add a layer so we can check if the service is running
@@ -857,7 +865,6 @@ def _charm_logging_ca_cert(self) -> Optional[str]:
 
     @property
     def _tsdb_versions_migration_dates(self) -> List[Dict[str, str]]:
-
         # If v13_migration_date isn't set (due to missing or failed retrieval),
         # we determine the migration date for v13 schema. This occurs once
         # during initial setup, as subsequent hooks will get the value from the persisted backup config.

src/config_builder.py

@@ -56,6 +56,7 @@ def __init__(
         http_tls: bool = False,
         tsdb_versions_migration_dates: Optional[List[Dict[str, str]]] = None,
         reporting_enabled: bool,
+        grafana_external_url: str,
     ):
         """Init method."""
         self.instance_addr = instance_addr
@@ -67,6 +68,7 @@ def __init__(
         self.retention_period = retention_period
         self.tsdb_versions_migration_dates = tsdb_versions_migration_dates or []
         self.reporting_enabled = reporting_enabled
+        self.grafana_external_url = grafana_external_url
 
     def build(self) -> dict:
         """Build Loki config dictionary."""
@@ -122,7 +124,8 @@ def _ruler(self) -> dict:
         # Reference: https://grafana.com/docs/loki/latest/configure/#ruler
         return {
             "alertmanager_url": self.alertmanager_url,
-            "external_url": self.external_url,
+            "external_url": self.grafana_external_url,
+            # "datasource_uid": "juju_am-test_3688ddf4-84ec-4f55-81da-5afc4166105d_loki_0",
             "enable_alertmanager_v2": True,
         }