OtlpClient-Program.cs

using System.Diagnostics;
using OpenTelemetry.Resources;
using OpenTelemetry.Trace;



var builder = WebApplication.CreateBuilder(args);
ActivitySource sSource = new ActivitySource(builder.Environment.ApplicationName);

// Add services to the container.
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddHttpClient("local",app =>
    {
        app.BaseAddress = new Uri("http://localhost:5118/");

    }
);

var tracingOtlpEndpoint = builder.Configuration.GetValue("Otlp:Endpoint", defaultValue: "http://localhost:4317")!;
var otel = builder.Services.AddOpenTelemetry();

// Configure OpenTelemetry Resources with the application name
otel.ConfigureResource(resource => resource
    .AddService(serviceName: builder.Environment.ApplicationName));
otel.WithTracing(tracing =>
{
    tracing.AddAspNetCoreInstrumentation();
    tracing.AddHttpClientInstrumentation();
    tracing.AddSource(sSource.Name );

    if (tracingOtlpEndpoint != null)
    {
        tracing.AddOtlpExporter(otlpOptions =>
        {
            otlpOptions.Endpoint = new Uri(tracingOtlpEndpoint); 
        });
    }
    // else
    // {
        tracing.AddConsoleExporter();
    //}
});

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.MapGet("/getweatherforecast", async () =>
    {
        using Activity activity = sSource.StartActivity("call GetWeatherAsync");
        return await GetWeatherAsync();
    })
    .WithName("GetWeatherForecast");

app.Run();

async Task<HttpResponseMessage> GetWeatherAsync()
{
    using Activity activity = sSource.StartActivity("exec GetWeatherAsync");
    activity?.SetTag("yowko", "tag OK");

    var httpclient = app.Services.GetService<IHttpClientFactory>().CreateClient("local");
    return await httpclient.GetAsync("/weatherforecast");
}

OtlpServer-Program.cs

using System.Diagnostics;
using OpenTelemetry.Resources;
using OpenTelemetry.Trace;


var builder = WebApplication.CreateBuilder(args);
ActivitySource sSource = new ActivitySource(builder.Environment.ApplicationName);

// Add services to the container.
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var tracingOtlpEndpoint = builder.Configuration.GetValue("Otlp:Endpoint", defaultValue: "http://localhost:4317")!;

var otel = builder.Services.AddOpenTelemetry();

// Configure OpenTelemetry Resources with the application name
otel.ConfigureResource(resource => resource
    .AddService(serviceName: builder.Environment.ApplicationName));

// Add Tracing for ASP.NET Core and our custom ActivitySource and export to Tempo
otel.WithTracing(tracing =>
{
    tracing.AddAspNetCoreInstrumentation();
    tracing.AddHttpClientInstrumentation();
    tracing.AddSource(sSource.Name);

    if (tracingOtlpEndpoint != null)
    {
        tracing.AddOtlpExporter(otlpOptions =>
        {
            otlpOptions.Endpoint = new Uri(tracingOtlpEndpoint); 
        });
    }
    else
    {
        tracing.AddConsoleExporter();
    }
});


var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

var summaries = new[]
{
    "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
};

app.MapGet("/weatherforecast", () =>
    {
        var forecast = Enumerable.Range(1, 5).Select(index =>
                new WeatherForecast
                (
                    DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
                    Random.Shared.Next(-20, 55),
                    summaries[Random.Shared.Next(summaries.Length)]
                ))
            .ToArray();
        return forecast;
    })
    .WithName("GetWeatherForecast");

app.Run();

record WeatherForecast(DateOnly Date, int TemperatureC, string? Summary)
{
    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);
}