OpenTelemetry

Adds OpenTelemetry-compatible metrics and tracing to Shuttle.Mediator by observing the Sending/Sent events already exposed on MediatorOptions — no changes are required to your participants.

Installation

dotnet add package Shuttle.Mediator.OpenTelemetry

Registration

services.AddMediator()
    .AddOpenTelemetry();

This subscribes to Sending/Sent on the shared MediatorOptions:

• Metrics – every send is recorded against a Meter named Shuttle.Mediator.
• Tracing – every send is wrapped in an Activity from an ActivitySource named Shuttle.Mediator, named after the message type and parented to whatever Activity.Current is ambient at the time.

The instrumentation is built on System.Diagnostics.ActivitySource / System.Diagnostics.Metrics.Meter directly, so this package has no dependency on the OpenTelemetry SDK — it only becomes "live" once something subscribes to those names, for example:

services.AddOpenTelemetry()
    .WithTracing(builder => builder.AddSource("Shuttle.Mediator"))
    .WithMetrics(builder => builder.AddMeter("Shuttle.Mediator"));

If you only want one of the two, call MediatorOptions.AddOpenTelemetryMetrics() / AddOpenTelemetryTracing() directly instead of AddOpenTelemetry():

services.AddOptions<MediatorOptions>().Configure(options => options.AddOpenTelemetryMetrics());

Metrics

Name	Instrument	Unit	Description
mediator.sends.started	Counter	{send}	Number of message sends started.
mediator.sends.completed	Counter	{send}	Number of message sends that completed successfully.
mediator.send.duration	Histogram	ms	Duration of a message send, from Sending to Sent.

All three are tagged with mediator.message.type (the sent message's runtime type).

MediatorOptions does not expose a "send failed" event, so if a participant throws, Sent never fires: that send is counted in mediator.sends.started but not in mediator.sends.completed, and does not contribute a mediator.send.duration measurement. No state leaks in that case — pending timing data is correlated against the caller's SendEventArgs instance via a ConditionalWeakTable, so it is garbage-collected along with it rather than accumulating.

Tracing

• Every IMediator.SendAsync call produces an Activity named after the message type, parented to whatever Activity.Current is ambient at the time — a caller's own span, an incoming ASP.NET Core request span, or none. It is tagged with mediator.message.type.
• For the same reason as above, a send whose participant throws never has its Activity stopped, so it will not appear in an exporter. It does not leak: the Activity is reachable only via the same ConditionalWeakTable correlation and is collected along with the caller's SendEventArgs.

Extension points

• MediatorTelemetry.ActivitySource / MediatorTelemetry.Meter – the shared instances used throughout, exposed so you can add your own spans or measurements under the same names.