OpenTelemetry and Azure Monitor Exporter support

[rossgrambo]

Why this PR?

This change adds support for using OpenTelemetry with Azure Monitor Exporter instead of Application Insights.

Visible Changes

1. There is a new package, Microsoft.FeatureManagement.Telemetry.AzureMonitor. This package looks very similar to Microsoft.FeatureManagement.Telemetry.ApplicationInsights and works similarly.
2. There is a new example. Named VariantAndAzureMonitorDemo. It is a clone of VariantAndTelemetry demo but uses OTel and Azure Monitor.

Migrating from .ApplicationInsights to .AzureMonitor

Package

Microsoft.FeatureManagement.Telemetry.AzureMonitor
// instead of
Microsoft.FeatureManagement.Telemetry.ApplicationInsights

Builder extension

builder.Services.AddFeatureManagement()
    .AddAzureMonitorTelemetry();
// instead of
builder.Services.AddFeatureManagement()
    .AddApplicationInsightsTelemetry();

Emitting events

_logger.LogInformation("{microsoft.custom_event.name} {ImageRating}", "Vote", rating);
// instead of
_telemetry.TrackEvent(
  "Vote",
  properties: null,
  metrics: new Dictionary<string, double>
  {
    { "ImageRating", rating }
  });

*Note: Even better, use High-performance logging, like the LoggerExtension.cs in the example.

[Copilot]

Pull request overview

This PR adds support for using OpenTelemetry with Azure Monitor Exporter as an alternative to Application Insights for feature flag telemetry. The implementation uses structured logging instead of direct TelemetryClient calls, making it more flexible and aligned with modern .NET logging patterns.

Key changes:

• New Microsoft.FeatureManagement.Telemetry.AzureMonitor package with OpenTelemetry-based telemetry
• New test project Tests.FeatureManagement.Telemetry.AzureMonitor with comprehensive test coverage
• New example application VariantAndAzureMonitorDemo demonstrating the usage

Reviewed changes

Copilot reviewed 38 out of 91 changed files in this pull request and generated 4 comments.

File	Description
src/Microsoft.FeatureManagement.Telemetry.AzureMonitor/*.cs	Core implementation of Azure Monitor telemetry using OpenTelemetry processors and structured logging
src/Microsoft.FeatureManagement.Telemetry.AzureMonitor/*.csproj	Package configuration with OpenTelemetry dependencies
tests/Tests.FeatureManagement.Telemetry.AzureMonitor/*.cs	Test suite covering telemetry logging and processor ordering
examples/VariantAndAzureMonitorDemo/*	Demo application showing migration from Application Insights to Azure Monitor

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[thompson-tomo]

Based on https://opentelemetry.io/docs/specs/semconv/feature-flags/feature-flags-events/#evaluation-event shouldn't this value already be a tag hence u could use that instead of baggage

[rossgrambo]

This code is solving a different problem. The idea is that we need to get the TargetingId onto other activities besides the feature evaluation event. For example

Incoming API Request (Activity 1 - TargetingHttpContextMiddleware sets TargetingId as baggage)
| Feature Evaluation event happens (TargetingId added as ActivityEvent tag)
| Request to other API (Activity 2)
| Response from other API (Activity 2 end - processor promotes baggage to tag)
| misc code
Returned result (Activity 1 end - processor promotes baggage to tag)

Now the Azure Monitor exporter will emit Activity 2 to the "dependencies" table (since it was an outgoing request) and include the custom dimension "TargetingId". Activity 1 is emitted to the "requests" table (with it's targeting id as well)

[thompson-tomo]

Wouldn't it be easier to implement this as otel processor/exporter?

[rossgrambo]

Good question.

The primary reason I went this route is that this pattern is already established and working in the ApplicationInsights event publisher. Additionally- we have better control over sampling here since the feature flag evaluation events can't be sampled for reliable results.

But yes, we could rewrite this as a processor in the future.

[thompson-tomo]

Based on https://opentelemetry.io/docs/specs/semconv/feature-flags/feature-flags-events/#evaluation-event shouldn't this value already be a tag hence u could use that instead of baggage