feat: enable out-of-order samples

charmcraft.yaml

@@ -254,6 +254,14 @@ config:
        Otherwise, the value is set to the greater of the setpoint or 100,000.
        Ref: https://prometheus.io/docs/prometheus/latest/feature_flags/#exemplars-storage
       type: int
+    out_of_order_time_window:
+      default: "0s"
+      description: |
+        The time window within which out-of-order samples are accepted for ingestion.
+        Supported units: s, m, h (Prometheus duration format; "m" is minutes).
+        Set to "0s" to disable (default).
+        See https://prometheus.io/docs/prometheus/latest/configuration/configuration/#tsdb
+      type: string
 
 actions:
   validate-configuration:

src/charm.py

@@ -339,6 +339,10 @@ def _on_collect_unit_status(self, event: CollectStatusEvent):
         if not is_valid_timespec(cast(str, retention_time)):
             event.add_status(BlockedStatus(f"Invalid time spec : {retention_time}"))
 
+        out_of_order_time_window = self.model.config.get("out_of_order_time_window", "")
+        if not is_valid_timespec(cast(str, out_of_order_time_window)):
+            event.add_status(BlockedStatus(f"Invalid time spec : {out_of_order_time_window}"))
+
         # "Push" statuses
         for status in self._stored.status.values():
             event.add_status(to_status(status))
@@ -1131,8 +1135,15 @@ def _generate_prometheus_config(self) -> bool:
 
         web_config = self._web_config()
 
+        storage_config = {}
         if self._exemplars:
-            prometheus_config["storage"] = {"exemplars": {"max_exemplars": self._exemplars}}
+            storage_config["exemplars"] = {"max_exemplars": self._exemplars}
+        if is_valid_timespec(
+            ooo := cast(str, self.model.config.get("out_of_order_time_window", ""))
+        ):
+            storage_config.setdefault("tsdb", {})["out_of_order_time_window"] = ooo
+        if storage_config:
+            prometheus_config["storage"] = storage_config
 
         if self.workload_tracing_endpoint:
             prometheus_config["tracing"] = self._tracing_config()

tests/unit/test_charm.py

@@ -175,7 +175,26 @@ def test_invalid_metrics_retention_times_can_not_be_set(self, *unused):
 
     @k8s_resource_multipatch
     @patch("lightkube.core.client.GenericSyncClient")
-    @prom_multipatch
+    def test_valid_out_of_order_time_window_can_be_set(self, *unused):
+        acceptable = ["5m", "1h", "30s", "0s"]
+        for value in acceptable:
+            self.harness.update_config({"out_of_order_time_window": value})
+            container = self.harness.charm.unit.get_container(self.harness.charm._name)
+            config = yaml.safe_load(container.pull(PROMETHEUS_CONFIG))
+            self.assertEqual(
+                config.get("storage", {}).get("tsdb", {}).get("out_of_order_time_window"), value
+            )
+
+    @k8s_resource_multipatch
+    @patch("lightkube.core.client.GenericSyncClient")
+    def test_invalid_out_of_order_time_window_can_not_be_set(self, *unused):
+        self.harness.update_config({"out_of_order_time_window": "5min"})
+        container = self.harness.charm.unit.get_container(self.harness.charm._name)
+        config = yaml.safe_load(container.pull(PROMETHEUS_CONFIG))
+        self.assertIsNone(config.get("storage", {}).get("tsdb"))
+
+    @k8s_resource_multipatch
+    @patch("lightkube.core.client.GenericSyncClient")
     def test_global_evaluation_interval_can_be_set(self, *unused):
         evalint_config = {}
         acceptable_units = ["y", "w", "d", "h", "m", "s"]