OTLP Exporter collects zero metrics on .NET MAUI Android AOT- System.Diagnostics.Metrics registration fails

[LosDavidos]

System.Diagnostics.Metrics completely fails under .NET MAUI Android AOT

Problem Summary

I'm experiencing complete failure of System.Diagnostics.Metrics when running a .NET MAUI Android application with AOT compilation enabled. The OpenTelemetry SDK initializes successfully, but no metrics are ever collected or exported.

Environment

• .NET Version: 10.0 (net10.0-android)
• Platform: Android (Samsung SM-A057G, Android 15)
• OpenTelemetry Version: 1.14.0
• AOT Configuration:

  <RunAOTCompilation>true</RunAOTCompilation>
  <AndroidAotMode>Hybrid</AndroidAotMode>
  <AndroidLinkMode>SdkOnly</AndroidLinkMode>

Configuration

services.AddOpenTelemetry()
    .ConfigureResource(resource => resource
        .AddService("MobileApp", serviceVersion: "1.0.0")
        .AddAttributes(new Dictionary<string, object>
        {
            { "device.platform", "android" },
            { "device.os", DeviceInfo.Platform.ToString() },
            { "device.model", DeviceInfo.Model }
        }))
    .WithMetrics(metrics => metrics
        .AddMeter("Mobile")
        .AddView("photo.capture.time", new ExplicitBucketHistogramConfiguration
        {
            Boundaries = new double[] { 100, 200, 300, 500, 1000, 2000, 5000, 10000 }
        })
        .AddOtlpExporter(options =>
        {
            options.Endpoint = new Uri("https://my-backend.com/metrics");
            options.Protocol = OtlpExportProtocol.HttpProtobuf;
        }));

// Create meters and instruments
var meter = new Meter("Mobile", "1.0.0");
var appLaunchCounter = meter.CreateCounter<long>("app.launch.total", "1", "Total app launches");
var photoCaptureTime = meter.CreateHistogram<double>("photo.capture.time", "ms", "Photo capture time");

// Record metrics
appLaunchCounter.Add(1);
photoCaptureTime.Record(1234.5);

Behavior Comparison

Debug Build (works perfectly)

Diagnostic output:

[DIAGNOSTICS] Meter.s_allMeters.Count: 5
[DIAGNOSTICS] MeterListener.InstrumentPublished: called 39 times
  ✅ Instrument: photo.taken.total
  ✅ Instrument: photo.capture.time
  ✅ Instrument: app.launch.total
  (... all instruments registered)

[CONSOLE-EXPORTER] Export batch size: 1
Metric: app.launch.total
  Value: 1
  Tags: device.platform=android, device.model=SM-A057G

Release Build with AOT (complete failure)

Diagnostic output:

[DIAGNOSTICS] Meter.s_allMeters.Count: 0  ← ⚠️ EMPTY!
[DIAGNOSTICS] MeterListener.InstrumentPublished: never called
  ⚠️ NO INSTRUMENTS PUBLISHED TO LISTENER

[CONSOLE-EXPORTER] Export batch size: 0
  ⚠️ EMPTY BATCH - No metrics collected!

Root Cause Analysis

I've traced this to the BCL level - when new Meter("Mobile", "1.0.0") is created under AOT compilation, the meter instance is constructed but never registered in the static Meter.s_allMeters field. This causes MeterListener.InstrumentPublished callbacks to never fire, which means OpenTelemetry SDK never sees any instruments.

To confirm this is not an OpenTelemetry issue, I created a simple test exporter:

public class ConsoleTestMetricExporter : BaseExporter<Metric>
{
    public override ExportResult Export(in Batch<Metric> batch)
    {
        var count = 0;
        foreach (var metric in batch)
        {
            count++;
            Console.WriteLine($"Metric: {metric.Name}, Value: {metric}");
        }
        
        Console.WriteLine($"[CONSOLE-EXPORTER] Batch size: {count}");
        
        if (count == 0)
        {
            Console.WriteLine("[CONSOLE-EXPORTER] ⚠️ EMPTY BATCH");
        }
        
        return ExportResult.Success;
    }
}

The exporter is called correctly, but the batch is always empty in AOT builds.

What I've Tried

• ✅ LinkerConfig.xml with <assembly fullname="System.Diagnostics.DiagnosticSource" preserve="All" />
• ✅ TrimmerRoots.xml preservation
• ✅ rd.xml runtime directives
• ✅ Disabled linking entirely (AndroidLinkMode=None) - problem persists
• ✅ Verified OpenTelemetry SDK initializes correctly (logs confirm MeterProvider is active)
• ✅ AppContext.SetSwitch("System.Diagnostics.Metrics.Meter.IsSupported", true);

None of these affect the core issue: meters don't register in Meter.s_allMeters under AOT.

Questions

1. Has anyone successfully collected metrics in .NET MAUI Android with AOT enabled? If so, what configuration did you use?

2. Is this a known limitation? Should I file an issue in dotnet/runtime since this appears to be a BCL problem rather than an OpenTelemetry issue?

3. Are there any AOT-compatible alternatives to System.Diagnostics.Metrics that work with OpenTelemetry SDK?

4. Would a custom exporter that bypasses System.Diagnostics.Metrics entirely be a reasonable approach, or is there a better solution?

Related Issues

• system.Diagnostics.Metrics doesn't add my counter in the instrument in case of dotnet MAUI applicaiton when running android emulator using OpenTelemetry  dotnet/maui#21165 - Similar report: metrics work on Windows, fail on Android
• Visualize a OpenTelemetry metric in Prometheus in a MAUI app #4634 - Discussion about MAUI metrics

Additional Context

I can provide full diagnostic logs, sample project, or any other information that would be helpful. The failure is 100% reproducible - Debug builds always work, Release+AOT builds always fail with empty metric batches.

Thank you for any guidance!

[martincostello]

Should I file an issue in dotnet/runtime since this appears to be a BCL problem rather than an OpenTelemetry issue?

Yes, if you're confident the root cause is there.

Are there any AOT-compatible alternatives to System.Diagnostics.Metrics that work with OpenTelemetry SDK?

Not that I'm aware of - the .NET OpenTelemetry SDK builds on top of the .NET APIs (Activity, Meter).

Would a custom exporter ...

I would hold off on that until you've filed a bug with dotnet/runtime - if it's a easily fixable bug that can be backported to servicing branches, then you may only need to wait ~2 months for a patch that fixes it.

---

FYI we have zero CI/test coverage for MAUI scenarios (see #5831). We do however have test coverage for native AoT.

[martincostello]

This issue might also be relevant: dotnet/runtime#120113

[martincostello]

Found the issue you filed. Cross-linking to the apparent answer: dotnet/runtime#124226 (comment)

[martincostello]

Also #4634 (comment)

[LosDavidos]

I've opened a ticket in the dotnet repo and it turned out that there is a parameter which disables metrics in release configuration for Android/iOS:
https://learn.microsoft.com/en-us/dotnet/ios/building-apps/build-properties#metricssupport

So <MetricsSupport>true</MetricsSupport> solves the problem.