OpenTelemetry Support in Arcus

[gverstraete]

Is your feature request related to a problem? Please describe.
Many things are moving towards OpenTelemetry, so I would encourage to also embrace this in Arcus.

Describe the solution you'd like
I would be good to be able to log to OpenTelemetry with .Log{whatwewanttodo}

Additional context
Please also concern simplification & justification.

Also apply this to the default web api template.

[stijnmoreels]

Some info related to this and migration from App Insights client SDK to OpenTelemetry using service-to-service correlation/distributed tracing.

Minimalistic setup:

var builder = new HostBuilder();

builder.ConfigureServices(services =>
{
    services.ConfigureOpenTelemetryTracerProvider((provider, traces) =>
    {
        traces.AddSource("<name-of-subscribed-activity>");
        traces.ConfigureResource(resource =>
        {
            resource.AddService("<my-cloud-name>", serviceInstanceId: "<my-cloud-instance>");
        });
    });
    
    services.AddOpenTelemetry()
            .UseAzureMonitor(options =>
            {
                options.ConnectionString = "InstrumentationKey=<key>";
            });
});

Logging dependencies/requests:

internal static class ILoggerExtensions
{
    public static void LogDependency(this ILogger _, string dependencyName, ActivitySource source, bool isSuccessful, DateTimeOffset startTime, TimeSpan duration, Dictionary<string, object> contextProperties)
    {
        using Activity? activity = source.StartActivity(name: dependencyName, kind: ActivityKind.Client, startTime: startTime);
        if (activity is null)
        {
            return;
        }

        activity.SetEndTime(activity.StartTimeUtc.Add(duration));
        activity.SetStatus(isSuccessful ? ActivityStatusCode.Ok : ActivityStatusCode.Error);

        foreach (KeyValuePair<string, object> property in contextProperties)
        {
            activity.SetTag(property.Key, property.Value);
        }
    }

    public static void LogRequest(this ILogger _, string requestName, ActivitySource source, bool isSuccessful, DateTimeOffset startTime, TimeSpan duration, Dictionary<string, object> contextProperties)
    {
        using Activity? activity = source.StartActivity(name: requestName, kind: ActivityKind.Server, startTime: startTime);
        if (activity is null)
        {
            return;
        }

        activity.SetEndTime(activity.StartTimeUtc.Add(duration));
        activity.SetStatus(isSuccessful ? ActivityStatusCode.Ok : ActivityStatusCode.Error);

        foreach (KeyValuePair<string, object> property in contextProperties)
        {
            activity.SetTag(property.Key, property.Value);
        }
    }
}

Thing is, that you don't need a ILogger; we could inject our own logging provider, but that would make it more complex and we don't have the budget (anymore) to provide entire custom-SDK implementations.

[fgheysels]

These are some interesting resources:
https://learn.microsoft.com/en-us/azure/azure-monitor/app/opentelemetry-dotnet-migrate?tabs=aspnetcore
https://learn.microsoft.com/en-us/dotnet/core/diagnostics/observability-with-otel#net-implementation-of-opentelemetry

When providing support for OTel, we'll have to keep on supporting our current approach for a certain period of time.

I believe the current extension methods that Arcus offers (LogCustomEvent, LogCustomMetric, ... ) can still be leveraged here. The behavior / implementation of those methods will depend based whether we're using OTel or not.