Add DisableTelemetry support using OpenTelemetry OTEL_SDK_DISABLED

[rajkumar-rangaraj]

Summary

Adds support for disabling telemetry via TelemetryConfiguration.DisableTelemetry property by leveraging OpenTelemetry SDK 1.15.0's OTEL_SDK_DISABLED environment variable.

Changes

Core Implementation

• TelemetryConfiguration.Build(): When DisableTelemetry is true, sets OTEL_SDK_DISABLED=true environment variable before creating the OpenTelemetry SDK, causing it to return no-op implementations

DI Support (AspNetCore/WorkerService)

• Updated AddTelemetryConfigAndClient() to apply IConfigureOptions<TelemetryConfiguration> and IPostConfigureOptions<TelemetryConfiguration> callbacks, enabling services.Configure<TelemetryConfiguration>() pattern
• Added TelemetryConfiguration injection in AzureMonitorExporterOptions.Configure to set OTEL_SDK_DISABLED in IConfiguration when DisableTelemetry is true

Tests

• Added TelemetryConfigurationOtelSdkDisabledTests with 2 tests validating the feature for non-DI scenarios
• Tests use [Collection("TelemetryClientTests")] to prevent parallel execution issues with environment variable manipulation

Documentation

• Updated docs/concepts.md with usage examples for both direct and DI scenarios
• Updated CHANGELOG.md

Usage

Non-DI:

var configuration = new TelemetryConfiguration
{
    ConnectionString = "...",
    DisableTelemetry = true
};
var tc = new TelemetryClient(configuration);

DI (ASP.NET Core / Worker Service):

// Must be called BEFORE AddApplicationInsightsTelemetry()
services.Configure<TelemetryConfiguration>(tc => tc.DisableTelemetry = true);
services.AddApplicationInsightsTelemetry();

Notes

• Requires OpenTelemetry SDK 1.15.0+ which supports OTEL_SDK_DISABLED
• For DI scenarios, DisableTelemetry must be configured before AddApplicationInsightsTelemetry() is called

[Copilot]

Pull request overview

This PR adds support for disabling telemetry collection via the TelemetryConfiguration.DisableTelemetry property by leveraging OpenTelemetry SDK 1.15.0's OTEL_SDK_DISABLED environment variable.

Changes:

• Added DisableTelemetry property support in non-DI scenarios by setting OTEL_SDK_DISABLED environment variable in TelemetryConfiguration.Build()
• Extended DI support to apply IConfigureOptions<TelemetryConfiguration> callbacks in the TelemetryConfiguration factory
• Implemented DI telemetry disabling by setting OTEL_SDK_DISABLED in IConfiguration via AzureMonitorExporterOptions Configure callback
• Added tests for non-DI scenarios and updated documentation

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
BASE/src/Microsoft.ApplicationInsights/Extensibility/TelemetryConfiguration.cs	Sets OTEL_SDK_DISABLED environment variable when building SDK; removes CreateFromConfiguration method
BASE/src/Microsoft.ApplicationInsights/TelemetryClientExtensions.cs	Changes StartOperation to return null instead of throwing ArgumentNullException when activity is null
NETCORE/src/Shared/Extensions/ApplicationInsightsExtensions.cs	Updates TelemetryConfiguration factory to apply IConfigureOptions and IPostConfigureOptions callbacks
NETCORE/src/Microsoft.ApplicationInsights.WorkerService/ApplicationInsightsExtensions.cs	Sets OTEL_SDK_DISABLED in IConfiguration when DisableTelemetry is true
NETCORE/src/Microsoft.ApplicationInsights.AspNetCore/Extensions/ApplicationInsightsExtensions.cs	Sets OTEL_SDK_DISABLED in IConfiguration when DisableTelemetry is true
BASE/Test/Microsoft.ApplicationInsights.Test/Microsoft.ApplicationInsights.Tests/TelemetryConfigurationOtelSdkDisabledTests.cs	Adds tests for DisableTelemetry in non-DI scenarios
docs/concepts.md	Documents DisableTelemetry usage for both non-DI and DI scenarios
CHANGELOG.md	Updates changelog with new feature entry
examples/AspNetCoreWebApp/Startup.cs	Adds commented example showing DisableTelemetry usage in DI
.publicApi/Microsoft.ApplicationInsights.dll/Stable/PublicAPI.Unshipped.txt	Removes CreateFromConfiguration method from public API

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