OpenTelemetry

The Nexum.OpenTelemetry package adds built-in distributed tracing and metrics. Every command, query, stream, and notification dispatch automatically creates an Activity with structured tags — no code changes required in your handlers.

Setup

dotnet add package Nexum.OpenTelemetry
dotnet add package OpenTelemetry.Extensions.Hosting
dotnet add package OpenTelemetry.Exporter.OpenTelemetryProtocol

using Nexum.OpenTelemetry;

builder.Services.AddNexum();

builder.Services.AddOpenTelemetry()
    .WithTracing(tracing => tracing
        .AddNexumInstrumentation()
        .AddOtlpExporter())
    .WithMetrics(metrics => metrics
        .AddNexumInstrumentation()
        .AddOtlpExporter());

Activity tags

Every dispatch emits an Activity on the Nexum ActivitySource with these tags:

Tag	Example	Description
`nexum.kind`	`command`, `query`, `stream`, `notification`	Kind of operation.
`nexum.type`	`CreateOrderCommand`	CLR name of the message type.
`nexum.namespace`	`Orders.Commands`	Namespace of the message type.
`nexum.handler`	`CreateOrderHandler`	Resolved handler type.
`nexum.result`	`success`, `failure`	Outcome of the dispatch.
`nexum.depth`	`1`	Nested dispatch depth at the time of the call.
`exception.type`	`ValidationException`	Set on failure.
`exception.message`	`OrderId cannot be empty`	Set on failure.

Metrics

The package exposes a Meter named Nexum with:

nexum.dispatch.duration (histogram, ms) — tagged by kind, type, result.
nexum.dispatch.count (counter) — tagged by kind, type, result.
nexum.notifications.fire_and_forget.queue_depth (observable gauge) — current channel depth.
nexum.notifications.fire_and_forget.dropped (counter) — messages dropped because the channel was full.

Correlation across dispatches

Because Nexum uses the standard System.Diagnostics.Activity API, parent/child correlation works automatically. A command dispatched from inside another handler becomes a child Activity, nested under the outer span.

Zero-overhead when disabled