# Configure OBI Prometheus and OpenTelemetry metrics histograms

> Configure metrics histograms for Prometheus and OpenTelemetry, and whether to use native histograms and exponential histograms.

---

LLMS index: [llms.txt](/llms.txt)

---

You can configure OBI Prometheus and OpenTelemetry metrics histograms. You can
also choose to use native histograms and exponential histograms.

## Override histogram buckets

You can override the histogram bucket boundaries for OpenTelemetry and
Prometheus metrics exporters by setting the `buckets` YAML configuration option:

YAML section: `otel_metrics_export.buckets`

For example:

```yaml
otel_metrics_export:
  buckets:
    duration_histogram: [0, 1, 2]
```

| YAML                 | Type        |
| -------------------- | ----------- |
| `duration_histogram` | `[]float64` |

Set the bucket boundaries for metrics related to request duration. Specifically:

- `http.server.request.duration` (OTel) / `http_server_request_duration_seconds`
  (Prometheus)
- `http.client.request.duration` (OTel) / `http_client_request_duration_seconds`
  (Prometheus)
- `rpc.server.duration` (OTel) / `rpc_server_duration_seconds` (Prometheus)
- `rpc.client.duration` (OTel) / `rpc_client_duration_seconds` (Prometheus)

If you leave the value unset, OBI uses the default bucket boundaries from the
[OpenTelemetry semantic conventions](/docs/specs/semconv/http/http-metrics/):

```text
0, 0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10
```

YAML section: `prometheus_export.buckets`

```yaml
prometheus_export:
  buckets:
    request_size_histogram: [0, 10, 20, 22]
    response_size_histogram: [0, 10, 20, 22]
```

| YAML                      | Type        |
| ------------------------- | ----------- |
| `request_size_histogram`  | `[]float64` |
| `response_size_histogram` | `[]float64` |

Set the bucket boundaries for metrics related to request and response sizes:

- `http.server.request.body.size` (OTel) / `http_server_request_body_size_bytes`
  (Prometheus)
- `http.client.request.body.size` (OTel) / `http_client_request_body_size_bytes`
  (Prometheus)
- `http.server.response.body.size` (OTel) /
  `http_server_response_body_size_bytes` (Prometheus)
- `http.client.response.body.size` (OTel) /
  `http_client_response_body_size_bytes` (Prometheus)

If you leave the value unset, OBI uses these default bucket boundaries:

```text
0, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192
```

These default values are UNSTABLE and may change if Prometheus or OpenTelemetry
semantic conventions recommend different bucket boundaries.

## Use native histograms and exponential histograms

For Prometheus, you enable
[native histograms](https://prometheus.io/docs/concepts/metric_types/#histogram)
by
[enabling the `native-histograms` feature in your Prometheus collector](https://prometheus.io/docs/prometheus/latest/feature_flags/#native-histograms).

For OpenTelemetry, you can use
[exponential histograms](/docs/specs/otel/metrics/data-model/#exponentialhistogram)
for the predefined histograms instead of defining the buckets manually. Set the
standard
[OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION](/docs/specs/otel/metrics/sdk_exporters/otlp/#additional-environment-variable-configuration)
environment variable. See the `histogram_aggregation` section in the
[OTel metrics exporter](../export-data/) section for more information.