Tracing MediatR using Application Insights in ASP.NET Core - asp.net-core

Question

What is the currently recommended way to trace MediatR using Application Insights in an ASP.NET Core Application?
Our goal is to drill down the individual pipelines in an application from Request, Mediator Call to Response.
Way 1: Wrap Mediator in an action
[HttpGet]
[Route("", Name = MachinesRoutes.Names.GetMachines)]
public async Task<IActionResult> GetMachines()
{
MachinesProjection p;
using (IOperationHolder<RequestTelemetry> operation = _telemetryClient.StartOperation<RequestTelemetry>(nameof(GetMachinesCommand)))
{
p = await _mediator.Send(new GetMachinesCommand());
}
// ....
}
Way 2: own dispatcher
public class MediatorDispatcher : IEventDispatcher
{
private readonly IMediator _mediator;
private readonly TelemetryClient _telemetryClient;
public MediatorDispatcher(IMediator mediator, TelemetryClient telemetryClient )
{
_mediator = mediator;
_telemetryClient = telemetryClient;
}
public async Task<TResponse> Send<TResponse>(IRequest<TResponse> command, CancellationToken cancellationToken = default)
{
using IOperationHolder<RequestTelemetry> operation = _telemetryClient.StartOperation<RequestTelemetry>(command.GetType().FullName);
return await _mediator.Send(command, cancellationToken).ConfigureAwait(false);
}
Way 3 ...?
In the end, we want to have a way to recognize requests that take an unusually long time.
It should also be possible to recognize what caused the request duration, i.e. a drill down of the operation.
Thanks.

Answer 1

I Agree with #Peter Bons . Behavior would be the most optimum way in your scenario.
behaviors, which allow you to build your own pipeline directly inside of MediatR without resolving to using decorators around your handlers. It's a more natural way to enhance your handlers with behavior and better supported in containers.
A pipeline behavior is an implementation of IPipelineBehavior. It represents a similar pattern to filters in ASP.NET MVC/Web API or pipeline behaviors in NServiceBus. Your pipeline behavior needs to implement one method:
Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next);
Two built-in behaviors exist:
RequestPreProcessorBehavior will execute IRequestPreProcessor implementations before any handlers are called
RequestPostProcessorBehavior will execute IRequestPostProcessor implementations after all handlers are called
You can find these in the MediatR.Pipeline namespace, and will need to be explicitly registered with your container as open generics.
Additionally, any IRequestPreProcessor and IRequestPostProcessor will need to be registered with the container.
You can find the sample pipeline here.
Hope it helps.