feat: expose histogram_bucket_overrides on OpenTelemetryConfig (#1433)

* Expose histogram_bucket_overrides on OpenTelemetryConfig

Mirror the existing PrometheusConfig.histogram_bucket_overrides field.
The underlying OtelCollectorOptions builder already supports this via
maybe_histogram_bucket_overrides; this change wires it through the
Python wrapper and pyo3 bridge.

* Add test for OpenTelemetry histogram_bucket_overrides

* Drop redundant test comment

* Fix runtime test lint

* fix: reformat test_runtime.py with ruff 0.15.15

The test-latest-deps CI job upgrades ruff to 0.15.15, which reformats
assert-with-message statements into the new preferred style.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: tconley1428 <tconley1428@gmail.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 3 people

temporalio/bridge/runtime.py

@@ -71,6 +71,7 @@ class OpenTelemetryConfig:
     metric_temporality_delta: bool
     durations_as_seconds: bool
     http: bool
+    histogram_bucket_overrides: Mapping[str, Sequence[float]] | None = None
 
 
 @dataclass(frozen=True)

temporalio/bridge/src/runtime.rs

@@ -75,6 +75,7 @@ pub struct OpenTelemetryConfig {
     metric_temporality_delta: bool,
     durations_as_seconds: bool,
     http: bool,
+    histogram_bucket_overrides: Option<HashMap<String, Vec<f64>>>,
 }
 
 #[derive(FromPyObject)]
@@ -357,6 +358,11 @@ impl TryFrom<MetricsConfig> for Arc<dyn CoreMeter> {
                 } else {
                     None
                 })
+                .maybe_histogram_bucket_overrides(otel_conf.histogram_bucket_overrides.map(
+                    |overrides| temporalio_common::telemetry::HistogramBucketOverrides {
+                        overrides,
+                    },
+                ))
                 .build();
             Ok(Arc::new(build_otlp_metric_exporter(otel_options).map_err(
                 |err| PyValueError::new_err(format!("Failed building OTel exporter: {err}")),

temporalio/runtime.py

@@ -336,6 +336,10 @@ class OpenTelemetryConfig:
             When enabled, the ``url`` should point to the HTTP endpoint
             (e.g. ``"http://localhost:4318/v1/metrics"``).
             Defaults to ``False`` (gRPC).
+        histogram_bucket_overrides: Override the default histogram bucket
+            boundaries for specific metrics. Keys are metric names and
+            values are sequences of bucket boundaries (e.g.
+            ``{"workflow_task_schedule_to_start_latency": [0.01, 0.05, 0.1, 0.5, 1.0, 5.0]}``).
     """
 
     url: str
@@ -346,6 +350,7 @@ class OpenTelemetryConfig:
     )
     durations_as_seconds: bool = False
     http: bool = False
+    histogram_bucket_overrides: Mapping[str, Sequence[float]] | None = None
 
     def _to_bridge_config(self) -> temporalio.bridge.runtime.OpenTelemetryConfig:
         return temporalio.bridge.runtime.OpenTelemetryConfig(
@@ -361,6 +366,7 @@ def _to_bridge_config(self) -> temporalio.bridge.runtime.OpenTelemetryConfig:
             ),
             durations_as_seconds=self.durations_as_seconds,
             http=self.http,
+            histogram_bucket_overrides=self.histogram_bucket_overrides,
         )
 
 

tests/test_runtime.py

@@ -4,7 +4,7 @@
 import re
 import uuid
 from datetime import timedelta
-from typing import cast
+from typing import Any, cast
 from urllib.request import urlopen
 
 import pytest
@@ -14,6 +14,7 @@
 from temporalio.runtime import (
     LogForwardingConfig,
     LoggingConfig,
+    OpenTelemetryConfig,
     PrometheusConfig,
     Runtime,
     TelemetryConfig,
@@ -269,6 +270,107 @@ async def check_metrics() -> None:
     await assert_eventually(check_metrics)
 
 
+async def test_opentelemetry_histogram_bucket_overrides(client: Client):
+    # Set up an OpenTelemetry configuration with custom histogram bucket overrides
+    import threading
+    from http.server import BaseHTTPRequestHandler, HTTPServer
+
+    from opentelemetry.proto.collector.metrics.v1.metrics_service_pb2 import (
+        ExportMetricsServiceRequest,
+        ExportMetricsServiceResponse,
+    )
+
+    special_value = float(1234.5678)
+    histogram_overrides = {
+        "temporal_long_request_latency": [special_value / 2, special_value],
+        "custom_histogram": [special_value / 2, special_value],
+    }
+
+    captured: dict[str, list[float]] = {}
+    lock = threading.Lock()
+
+    class Handler(BaseHTTPRequestHandler):
+        def log_message(self, format: str, *args: Any):
+            pass  # silence default stderr logging
+
+        def do_POST(self):
+            length = int(self.headers.get("Content-Length", "0"))
+            req = ExportMetricsServiceRequest()
+            req.ParseFromString(self.rfile.read(length))
+            with lock:
+                for rm in req.resource_metrics:
+                    for sm in rm.scope_metrics:
+                        for m in sm.metrics:
+                            if m.HasField("histogram"):
+                                for dp in m.histogram.data_points:
+                                    captured[m.name] = list(dp.explicit_bounds)
+            body = ExportMetricsServiceResponse().SerializeToString()
+            self.send_response(200)
+            self.send_header("Content-Type", "application/x-protobuf")
+            self.send_header("Content-Length", str(len(body)))
+            self.end_headers()
+            self.wfile.write(body)
+
+    otel_port = find_free_port()
+    server = HTTPServer(("127.0.0.1", otel_port), Handler)
+    thread = threading.Thread(target=server.serve_forever, daemon=True)
+    thread.start()
+    try:
+        runtime = Runtime(
+            telemetry=TelemetryConfig(
+                metrics=OpenTelemetryConfig(
+                    url=f"http://127.0.0.1:{otel_port}/v1/metrics",
+                    http=True,
+                    metric_periodicity=timedelta(milliseconds=100),
+                    durations_as_seconds=False,
+                    histogram_bucket_overrides=histogram_overrides,
+                ),
+            ),
+        )
+
+        # Create and record to a custom histogram
+        custom_histogram = runtime.metric_meter.create_histogram(
+            "custom_histogram", "Custom histogram", "ms"
+        )
+        custom_histogram.record(600)
+
+        # Run a workflow so built-in histograms (e.g. temporal_long_request_latency)
+        # are recorded and exported.
+        client_with_overrides = await Client.connect(
+            client.service_client.config.target_host,
+            namespace=client.namespace,
+            runtime=runtime,
+        )
+        task_queue = f"task-queue-{uuid.uuid4()}"
+        async with Worker(
+            client_with_overrides,
+            task_queue=task_queue,
+            workflows=[HelloWorkflow],
+        ):
+            assert "Hello, World!" == await client_with_overrides.execute_workflow(
+                HelloWorkflow.run,
+                "World",
+                id=f"workflow-{uuid.uuid4()}",
+                task_queue=task_queue,
+            )
+
+        async def check_metrics() -> None:
+            with lock:
+                snapshot = dict(captured)
+            for key, buckets in histogram_overrides.items():
+                assert key in snapshot, (
+                    f"Missing {key} in captured metrics: {list(snapshot)}"
+                )
+                assert snapshot[key] == pytest.approx(buckets), (
+                    f"Bucket mismatch for {key}: got {snapshot[key]} expected {buckets}"
+                )
+
+        await assert_eventually(check_metrics)
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
 def test_runtime_options_invalid_heartbeat() -> None:
     with pytest.raises(ValueError):
         Runtime(