Add docs for fluss-metrics-opentelemetry

Author: michaelkoepf

website/docs/maintenance/observability/metric-reporters.md

@@ -12,7 +12,7 @@ reporters will be instantiated on each CoordinatorServer and TabletServers when
 Example reporter configuration that specifies multiple reporters:
 
 ```yaml
-metrics.reporters: jmx,prometheus
+metrics.reporters: jmx,opentelemetry
 ```
 
 ## Push vs. Pull
@@ -57,6 +57,34 @@ An example for such a list would be `cluster_id=fluss1,host=localhost,server_id=
 
 The domain thus identifies a metric class, while the key-property list identifies one (or multiple) instances of that metric.
 
+### OpenTelemetry
+
+Type: push
+
+Parameters:
+
+- `metrics.reporter.opentelemetry.endpoint` - Target to which the OpenTelemetry metric reporter is going to send metrics to.
+- `metrics.reporter.opentelemetry.exporter` - The type of exporter that is used by the OpenTelemetry metric exporter to send metrics to the configured endpoint. The endpoint must accept connections for the given exporter type. Supported exporters: GRPC, HTTP.
+- `metrics.reporter.opentelemetry.export-interval` - (optional) Frequency of metric export by the OpenTelemetry metric reporter to the endpoint. Default: 10s.
+- `metrics.reporter.opentelemetry.export-timeout` - (optional) Maximum time the OpenTelemetry metric reporter will wait for each metric export. Default: 10s.
+
+Example configuration:
+
+```yaml
+metrics.reporters: opentelemetry
+metrics.reporter.opentelemetry.exporter: GRPC
+metrics.reporter.opentelemetry.endpoint: http://opentelemetry-collector:4317
+```
+
+Fluss metric types are mapped to OpenTelemetry metric types as follows:
+
+| Fluss     | OpenTelemetry           | Note                                                          |
+|-----------|-------------------------|---------------------------------------------------------------|
+| Counter   | LONG_SUM                |                                                               |
+| Gauge     | LONG_GAUGE/DOUBLE_GAUGE | Automatically determined by the type of the Gauge.            |
+| Histogram | SUMMARY                 | Quantiles .5, .75, .95, .99                                   |
+| Meter     | LONG_SUM, DOUBLE_GAUGE  | Exports the meter's count (LONG_SUM) and rate (DOUBLE_GAUGE). |
+
 ### Prometheus
 
 Type: pull
@@ -74,9 +102,9 @@ metrics.reporter.prometheus.port: 9250
 
 Fluss metric types are mapped to Prometheus metric types as follows:
 
-| Fluss     | Prometheus | Note                                     |
-| --------- |------------|------------------------------------------|
-| Counter   | Gauge      |Prometheus counters cannot be decremented.|
-| Gauge     | Gauge      |Only numbers and booleans are supported.  |
-| Histogram | Summary    |Quantiles .5, .75, .95, .98, .99 and .999 |
-| Meter     | Gauge      |The gauge exports the meter's rate.       |
+| Fluss     | Prometheus | Note                                       |
+|-----------|------------|--------------------------------------------|
+| Counter   | Gauge      | Prometheus counters cannot be decremented. |
+| Gauge     | Gauge      | Only numbers and booleans are supported.   |
+| Histogram | Summary    | Quantiles .5, .75, .95, .98, .99 and .999  |
+| Meter     | Gauge      | The gauge exports the meter's rate.        |