Update cos_agent lib with generic HostHealth rules (#232)

* Remove host_health.rules file in favour of generic alert rules
* Inject generic alert rules via `cos_agent`
* Import central rule groups from cos-lib

lib/charms/grafana_agent/v0/cos_agent.py

@@ -235,7 +235,7 @@ def __init__(self, *args):
 
 import pydantic
 from cosl import DashboardPath40UID, JujuTopology, LZMABase64
-from cosl.rules import AlertRules
+from cosl.rules import AlertRules, generic_alert_groups
 from ops.charm import RelationChangedEvent
 from ops.framework import EventBase, EventSource, Object, ObjectEvents
 from ops.model import ModelError, Relation
@@ -254,7 +254,7 @@ class _MetricsEndpointDict(TypedDict):
 
 LIBID = "dc15fa84cef84ce58155fb84f6c6213a"
 LIBAPI = 0
-LIBPATCH = 17
+LIBPATCH = 18
 
 PYDEPS = ["cosl >= 0.0.50", "pydantic"]
 
@@ -268,7 +268,6 @@ class _MetricsEndpointDict(TypedDict):
 logger = logging.getLogger(__name__)
 SnapEndpoint = namedtuple("SnapEndpoint", "owner, name")
 
-
 # Note: MutableMapping is imported from the typing module and not collections.abc
 # because subscripting collections.abc.MutableMapping was added in python 3.9, but
 # most of our charms are based on 20.04, which has python 3.8.
@@ -732,6 +731,10 @@ def _metrics_alert_rules(self) -> Dict:
             query_type="promql", topology=JujuTopology.from_charm(self._charm)
         )
         alert_rules.add_path(self._metrics_rules, recursive=self._recursive)
+        alert_rules.add(
+            generic_alert_groups.application_rules,
+            group_name_prefix=JujuTopology.from_charm(self._charm).identifier,
+        )
         return alert_rules.as_dict()
 
     @property

tests/scenario/test_cos_agent_e2e.py

@@ -9,6 +9,7 @@
     COSAgentProvider,
     COSAgentRequirer,
 )
+from cosl.rules import generic_alert_groups
 from ops.charm import CharmBase
 from ops.framework import Framework
 from ops.testing import Context, PeerRelation, State, SubordinateRelation
@@ -119,6 +120,25 @@ def requirer_ctx(requirer_charm):
     return Context(charm_type=requirer_charm, meta=requirer_charm.META)
 
 
+def test_cos_agent_injects_generic_alerts(provider_ctx):
+    # GIVEN a cos-agent subordinate relation
+    cos_agent = SubordinateRelation("cos-agent")
+
+    # WHEN the relation_changed event fires
+    state_out = provider_ctx.run(
+        provider_ctx.on.relation_changed(relation=cos_agent, remote_unit=1),
+        State(relations=[cos_agent]),
+    )
+
+    config = json.loads(
+        state_out.get_relation(cos_agent.id).local_unit_data[CosAgentPeersUnitData.KEY]
+    )
+    # THEN the metrics_alert_rules groups should only contain the generic alert groups
+    assert (
+        config["metrics_alert_rules"]["groups"] == generic_alert_groups.application_rules["groups"]
+    )
+
+
 def test_cos_agent_changed_no_remote_data(provider_ctx):
     cos_agent = SubordinateRelation("cos-agent")
 
@@ -130,7 +150,15 @@ def test_cos_agent_changed_no_remote_data(provider_ctx):
     config = json.loads(
         state_out.get_relation(cos_agent.id).local_unit_data[CosAgentPeersUnitData.KEY]
     )
-    assert config["metrics_alert_rules"] == {}
+
+    # the cos_agent lib injects generic (HostHealth) alert rules and should be filtered for the test
+    config["metrics_alert_rules"]["groups"] = [
+        group
+        for group in config["metrics_alert_rules"]["groups"]
+        if "_HostHealth_" not in group["name"]
+    ]
+
+    assert config["metrics_alert_rules"] == {"groups": []}
     assert config["log_alert_rules"] == {}
     assert len(config["dashboards"]) == 1
     assert len(config["metrics_scrape_jobs"]) == 1