Add support for OTEL_SDK_DISABLED environment variable

src/OpenTelemetry/CHANGELOG.md

@@ -6,6 +6,10 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+* Added support for the `OTEL_SDK_DISABLED` environment variable in TracerProvider,
+  MeterProvider, and LoggerProvider. When `OTEL_SDK_DISABLED=true`,
+  the SDK returns no-op implementations for all telemetry signals.
+  ([#6568](https://github.com/open-telemetry/opentelemetry-dotnet/pull/6568))
 * Fixed an issue where the Base2 Exponential Bucket Histogram did not reset its
   scale to 20 after each collection cycle when using delta aggregation temporality.
   ([#6557](https://github.com/open-telemetry/opentelemetry-dotnet/pull/6557))

src/OpenTelemetry/Logs/Builder/LoggerProviderBuilderBase.cs

@@ -1,9 +1,11 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
+using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using OpenTelemetry.Internal;
+using static OpenTelemetry.OpenTelemetrySdk;
 
 namespace OpenTelemetry.Logs;
 
@@ -39,7 +41,15 @@ internal LoggerProviderBuilderBase(IServiceCollection services)
 
         services
             .AddOpenTelemetryLoggerProviderBuilderServices()
-            .TryAddSingleton<LoggerProvider>(sp => new LoggerProviderSdk(sp, ownsServiceProvider: false));
+            .TryAddSingleton<LoggerProvider>(sp =>
+            {
+                if (IsOtelSdkDisabled(sp.GetRequiredService<IConfiguration>()))
+                {
+                    return new NoopLoggerProvider();
+                }
+
+                return new LoggerProviderSdk(sp, ownsServiceProvider: false);
+            });
 
         this.innerBuilder = new LoggerProviderServiceCollectionBuilder(services);
 
@@ -91,7 +101,25 @@ internal LoggerProvider Build()
         bool validateScopes = false;
 #endif
         var serviceProvider = services.BuildServiceProvider(validateScopes);
+        var configuration = serviceProvider.GetRequiredService<IConfiguration>();
+
+        if (IsOtelSdkDisabled(configuration))
+        {
+            serviceProvider.Dispose();
+            return new NoopLoggerProvider();
+        }
 
         return new LoggerProviderSdk(serviceProvider, ownsServiceProvider: true);
     }
+
+    private static bool IsOtelSdkDisabled(IConfiguration configuration)
+    {
+        bool isDisabled = configuration.TryGetBoolValue(OpenTelemetrySdkEventSource.Log, SdkConfigDefinitions.SdkDisableEnvVarName, out bool result) && result;
+        if (isDisabled)
+        {
+            OpenTelemetrySdkEventSource.Log.LoggerProviderSdkEvent($"Disabled because {SdkConfigDefinitions.SdkDisableEnvVarName} is true.");
+        }
+
+        return isDisabled;
+    }
 }

src/OpenTelemetry/Metrics/Builder/MeterProviderBuilderBase.cs

@@ -1,9 +1,11 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
+using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using OpenTelemetry.Internal;
+using static OpenTelemetry.OpenTelemetrySdk;
 
 namespace OpenTelemetry.Metrics;
 
@@ -39,7 +41,15 @@ internal MeterProviderBuilderBase(IServiceCollection services)
 
         services
             .AddOpenTelemetryMeterProviderBuilderServices()
-            .TryAddSingleton<MeterProvider>(sp => new MeterProviderSdk(sp, ownsServiceProvider: false));
+            .TryAddSingleton<MeterProvider>(sp =>
+            {
+                if (IsOtelSdkDisabled(sp.GetRequiredService<IConfiguration>()))
+                {
+                    return new NoopMeterProvider();
+                }
+
+                return new MeterProviderSdk(sp, ownsServiceProvider: false);
+            });
 
         this.innerBuilder = new MeterProviderServiceCollectionBuilder(services);
 
@@ -108,7 +118,25 @@ protected MeterProvider Build()
         bool validateScopes = false;
 #endif
         var serviceProvider = services.BuildServiceProvider(validateScopes);
+        var configuration = serviceProvider.GetRequiredService<IConfiguration>();
+
+        if (IsOtelSdkDisabled(configuration))
+        {
+            serviceProvider.Dispose();
+            return new NoopMeterProvider();
+        }
 
         return new MeterProviderSdk(serviceProvider, ownsServiceProvider: true);
     }
+
+    private static bool IsOtelSdkDisabled(IConfiguration configuration)
+    {
+        bool isDisabled = configuration.TryGetBoolValue(OpenTelemetrySdkEventSource.Log, SdkConfigDefinitions.SdkDisableEnvVarName, out bool result) && result;
+        if (isDisabled)
+        {
+            OpenTelemetrySdkEventSource.Log.MeterProviderSdkEvent($"Disabled because {SdkConfigDefinitions.SdkDisableEnvVarName} is true.");
+        }
+
+        return isDisabled;
+    }
 }

src/OpenTelemetry/SdkConfigDefinitions.cs

@@ -0,0 +1,9 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+namespace OpenTelemetry;
+
+internal static class SdkConfigDefinitions
+{
+    public const string SdkDisableEnvVarName = "OTEL_SDK_DISABLED";
+}

src/OpenTelemetry/Trace/Builder/TracerProviderBuilderBase.cs

@@ -1,9 +1,11 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
+using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using OpenTelemetry.Internal;
+using static OpenTelemetry.OpenTelemetrySdk;
 
 namespace OpenTelemetry.Trace;
 
@@ -39,7 +41,15 @@ internal TracerProviderBuilderBase(IServiceCollection services)
 
         services
             .AddOpenTelemetryTracerProviderBuilderServices()
-            .TryAddSingleton<TracerProvider>(sp => new TracerProviderSdk(sp, ownsServiceProvider: false));
+            .TryAddSingleton<TracerProvider>(sp =>
+            {
+                if (IsOtelSdkDisabled(sp.GetRequiredService<IConfiguration>()))
+                {
+                    return new NoopTracerProvider();
+                }
+
+                return new TracerProviderSdk(sp, ownsServiceProvider: false);
+            });
 
         this.innerBuilder = new TracerProviderServiceCollectionBuilder(services);
 
@@ -146,7 +156,25 @@ protected TracerProvider Build()
         bool validateScopes = false;
 #endif
         var serviceProvider = services.BuildServiceProvider(validateScopes);
+        var configuration = serviceProvider.GetRequiredService<IConfiguration>();
+
+        if (IsOtelSdkDisabled(configuration))
+        {
+            serviceProvider.Dispose();
+            return new NoopTracerProvider();
+        }
 
         return new TracerProviderSdk(serviceProvider, ownsServiceProvider: true);
     }
+
+    private static bool IsOtelSdkDisabled(IConfiguration configuration)
+    {
+        bool isDisabled = configuration.TryGetBoolValue(OpenTelemetrySdkEventSource.Log, SdkConfigDefinitions.SdkDisableEnvVarName, out bool result) && result;
+        if (isDisabled)
+        {
+            OpenTelemetrySdkEventSource.Log.TracerProviderSdkEvent($"Disabled because {SdkConfigDefinitions.SdkDisableEnvVarName} is true.");
+        }
+
+        return isDisabled;
+    }
 }

test/OpenTelemetry.Tests/EnvironmentVariableScope.cs

@@ -0,0 +1,17 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+internal sealed class EnvironmentVariableScope : IDisposable
+{
+    private readonly string name;
+    private readonly string? previous;
+
+    public EnvironmentVariableScope(string name, string? value)
+    {
+        this.name = name;
+        this.previous = Environment.GetEnvironmentVariable(name);
+        Environment.SetEnvironmentVariable(name, value);
+    }
+
+    public void Dispose() => Environment.SetEnvironmentVariable(this.name, this.previous);
+}

test/OpenTelemetry.Tests/Logs/LoggerProviderBuilderBaseTests.cs

@@ -0,0 +1,26 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+using Xunit;
+using static OpenTelemetry.OpenTelemetrySdk;
+
+namespace OpenTelemetry.Logs.Tests;
+
+public sealed class LoggerProviderBuilderBaseTests
+{
+    [Theory]
+    [InlineData("true", typeof(NoopLoggerProvider))]
+    [InlineData("false", typeof(LoggerProviderSdk))]
+    [InlineData(null, typeof(LoggerProviderSdk))]
+    public void LoggerProviderIsExpectedType(string? value, Type expected)
+    {
+        using (new EnvironmentVariableScope("OTEL_SDK_DISABLED", value))
+        {
+            var builder = new LoggerProviderBuilderBase();
+
+            using var provider = builder.Build();
+
+            Assert.IsType(expected, provider);
+        }
+    }
+}

test/OpenTelemetry.Tests/Metrics/MeterProviderBuilderBaseTests.cs

@@ -0,0 +1,26 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+using Xunit;
+using static OpenTelemetry.OpenTelemetrySdk;
+
+namespace OpenTelemetry.Metrics.Tests;
+
+public sealed class MeterProviderBuilderBaseTests
+{
+    [Theory]
+    [InlineData("true", typeof(NoopMeterProvider))]
+    [InlineData("false", typeof(MeterProviderSdk))]
+    [InlineData(null, typeof(MeterProviderSdk))]
+    public void LoggerProviderIsExpectedType(string? value, Type expected)
+    {
+        using (new EnvironmentVariableScope("OTEL_SDK_DISABLED", value))
+        {
+            var builder = new MeterProviderBuilderBase();
+
+            using var provider = builder.Build();
+
+            Assert.IsType(expected, provider);
+        }
+    }
+}

test/OpenTelemetry.Tests/Trace/TracerProviderBuilderBaseTests.cs

@@ -2,11 +2,28 @@
 // SPDX-License-Identifier: Apache-2.0
 
 using Xunit;
+using static OpenTelemetry.OpenTelemetrySdk;
 
 namespace OpenTelemetry.Trace.Tests;
 
-public class TracerProviderBuilderBaseTests
+public sealed class TracerProviderBuilderBaseTests
 {
+    [Theory]
+    [InlineData("true", typeof(NoopTracerProvider))]
+    [InlineData("false", typeof(TracerProviderSdk))]
+    [InlineData(null, typeof(TracerProviderSdk))]
+    public void TracerProviderIsExpectedType(string? value, Type expected)
+    {
+        using (new EnvironmentVariableScope("OTEL_SDK_DISABLED", value))
+        {
+            var builder = new TestTracerProviderBuilder();
+
+            using var provider = builder.Build();
+
+            Assert.IsType(expected, provider);
+        }
+    }
+
     [Fact]
     public void AddInstrumentationInvokesFactoryTest()
     {