ToolUp.Metrics.OpenTelemetry 0.22.0

ToolUp.Metrics.OpenTelemetry

OpenTelemetry-compatible metrics sink for the ToolUp Platform SDK (Phase 9e).

What it does

Implements IMetricsSink against the BCL System.Diagnostics.Metrics.Meter API. Meter is the OTel-native metric primitive on .NET 10 — the OpenTelemetry SDK consumes Meter instances and exports them to OTLP, Prometheus, Console, or any registered exporter.

Composing this companion alongside the SDK's in-process PrometheusMetricsSink gives every Increment / Record / SetGauge call two destinations: the in-process Prometheus registry (scraped at /metrics) and the BCL Meter (consumed by whatever OTel SDK the deployment configures).

What it does NOT do

This companion does NOT take a NuGet dependency on the OpenTelemetry SDK. The interface point is BCL Meter; the deployment owns the SDK's lifecycle (sampling, resource attributes, batch reader cadence, OTLP endpoint configuration). The split keeps this companion lean — apps that don't need OTLP export pay only the cost of a few BCL Counter<double> / Histogram<double> instruments.

Enabling

1. Add the project reference and the props injection in your server project:

   <Import Project="..\Metrics\OpenTelemetry\ToolUp.Metrics.OpenTelemetry.Server.props" />
   <ProjectReference Include="..\Metrics\OpenTelemetry\ToolUp.Metrics.OpenTelemetry.fsproj" />
   

2. In your composition root, register the sink alongside the in-process default:

   open ToolUp.Platform.Metrics
   open ToolUp.Platform.Metrics.OpenTelemetry
   
   let otelSink =
       OtelMetricsSink.create StandardMetrics.registrations resolvedLogger
   
   ServerApp.empty
   |> ServerApp.withConfig { config with MetricsEndpoint = EnabledMetricsEndpoint }
   |> ServerApp.withMetricsSink otelSink
   |> ServerApp.run
   

3. To export to OTLP (the standard OTel collector format), add the exporter NuGet to your server project's paket.references:

   OpenTelemetry
   OpenTelemetry.Exporter.OpenTelemetryProtocol
   

   And in your Program.fs:

   open OpenTelemetry
   open OpenTelemetry.Metrics
   
   let meterProvider =
       Sdk.CreateMeterProviderBuilder()
           .AddMeter("ToolUp")
           .AddOtlpExporter(fun opts ->
               // Defaults to OTEL_EXPORTER_OTLP_ENDPOINT env var
               // (http://localhost:4317 if unset). Override here to
               // pin the endpoint inline.
               opts.Endpoint <- System.Uri("http://your-collector:4317"))
           .Build()
   

How it composes

When ServerApp.withMetricsSink otelSink is wired in alongside MetricsEndpoint = EnabledMetricsEndpoint, compose folds the in-process PrometheusMetricsSink and every registered companion sink into a FanOutMetricsSink. A single Increment call dispatches to all sinks. The Prometheus sink is always at the head of the list so /metrics keeps returning current values even if the OTel exporter is down.

Cardinality

The per-metric series-count cap is enforced by the in-process PrometheusMetricsSink at the head of the fan-out chain. Emissions past the cap fold into _overflow="true" before reaching this companion. The OTel SDK's MeterProviderBuilder.SetMaxMetricStreams is the natural place for an additional ceiling on the export side.

Six-rule portability audit