Add activity source to allow OpenTelemetry to collect tracing

[zhiyuanliang-ms]

Why this PR?

OpenTelemetry tracing in .NET is built on Activity.

Only Activity from ActivitySource which is registered to TracerProvider by AddSource method will be traced by OpenTelemetry. （Implementation details: TracerProviderSdk OTEL will create activity listener to trace activities.)

This PR adds an ActivitySource with name called "Microsoft.Extensions.Configuration.AzureAppConfiguration" to allow OpenTelemetry to collect tracing for the Load and Refresh activities.

Bug fixes

Activity created by the .NET SDK(ConfigurationClient) cannot be traced because of the request tracing in .NET provider which is built on "CustomDiagnosticsHeaders" activity.

Below are the implementation details of the request tracing in .NET SDK and .NET provider:
Request tracing hook: SDK, provider

The .NET provider will start a new Activity with no source/listener. This activity will have ActivityTraceFlags set to ActivityTraceFlags.None. According to doc, this kind of activity will not be traced. And the activity created by the ConfigurationClient from SDK will be the child activity of the activity we created and it will inherit the ActivityTraceFlags which will cause the child activity not to be traced.

The below code demostrates the issue in a simplified way:

using System.Diagnostics;
using OpenTelemetry.Trace;

var builder = Host.CreateApplicationBuilder(args);

List<Activity> exportedActivities = new();
var activitySource = new ActivitySource("TestSource"); // mocked activity source of ConfigurationClient

builder.Services.AddOpenTelemetry()
    .WithTracing(builder =>
    {
        builder.AddInMemoryExporter(exportedActivities)
            .AddSource(["TestSource"]); // OTEL sdk will create an ActivityListener to listen to the registered ActivitySource
    });


using (var host = builder.Build())
{
    host.Start();
    var activityWithoutSource = new Activity("mocked activity started by .NET provider for request tracing");
    activityWithoutSource.Start();
    Console.WriteLine(Activity.Current?.DisplayName);
    Console.WriteLine(Activity.Current?.ActivityTraceFlags);
    //Activity.Current.ActivityTraceFlags = ActivityTraceFlags.Recorded; // if we manually set the flag to Recorded, then the activity below will then be catched by OTEL

    var testActivity = activitySource.StartActivity("mocked activity created by ConfigurationClient");
    Console.WriteLine(Activity.Current?.DisplayName);
    Console.WriteLine(Activity.Current?.ActivityTraceFlags); // the child activity will inherit the ActivityTraceFlags from its parent activity
    testActivity?.Stop();

    activityWithoutSource.Stop();

    Console.WriteLine(exportedActivities.Count());
    if (exportedActivities.Count() > 0)
    {
        Console.WriteLine(exportedActivities[0].OperationName);
    }
}

Verify that request tracing can work with the change in this PR

Currently, we are lacking testcases about request tracing in this repo.

The following code can be used to verify that the request tracing won't be effected. (OpenTelemetry.Extensions.Hosting and OpenTelemetry.Exporter.InMemory packages are required)

using Azure.Data.AppConfiguration;
using System.Diagnostics;
using OpenTelemetry.Trace;

var builder = Host.CreateApplicationBuilder(args);

var client = new ConfigurationClient("<connection-string>");
List<Activity> exportedActivities = new();

builder.Services.AddOpenTelemetry()
    .WithTracing(builder =>
    {
        builder.AddInMemoryExporter(exportedActivities)
            //.AddSource([$"{typeof(ConfigurationClient).Namespace}.*", "ConfigurationProvider"]);
            .AddSource(["ConfigurationProvider"]);
        //.AddSource([$"{typeof(ConfigurationClient).Namespace}.*"]);
    });

var activitySource = new ActivitySource("ConfigurationProvider");

using (var host = builder.Build())
{
    host.Start();

    using (var refreshActivity = activitySource.StartActivity("Refresh"))
    {
        Console.WriteLine($"refreshActivity is null: {refreshActivity == null}");

        var requestTracingActivity = new Activity("Azure.CustomDiagnosticHeaders");
        requestTracingActivity.Start();
        client.GetConfigurationSetting("test"); // the SDK has its own activity source: "Azure.Data.AppConfiguration.ConfigurationClient"
                                                // Add breakpoint in the SDK's CustomHeadersPolicy.cs file can verify that the "CustomDiagnosticHeaders" activity will be catched.
        requestTracingActivity.Stop();
    }

    Console.WriteLine(exportedActivities.Count());
    if (exportedActivities.Count() > 0)
    {
        Console.WriteLine(exportedActivities[0].OperationName);
    }
}