Fix: OtlpExporterOptions is not picking up env variables

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/CHANGELOG.md

@@ -7,6 +7,12 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+* Fixed an issue where `OtlpExporterOptions` did not read environment variables (e.g. `OTEL_EXPORTER_OTLP_ENDPOINT`)
+  if the environment variables were set after `IConfiguration` was built.
+  ([#6558](https://github.com/open-telemetry/opentelemetry-dotnet/issues/6558))
+  This change also addresses similar issues when .Net `Host` does not load environment variables into `IConfiguration` (e.g. `Host.CreateEmptyApplicationBuilder`).
+  ([#5586](https://github.com/open-telemetry/opentelemetry-dotnet/issues/5586))
+
 ## 1.13.0
 
 Released 2025-Oct-01

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/OtlpExporterOptions.cs

@@ -48,27 +48,33 @@ public class OtlpExporterOptions : IOtlpExporterOptions
     /// Initializes a new instance of the <see cref="OtlpExporterOptions"/> class.
     /// </summary>
     public OtlpExporterOptions()
-        : this(OtlpExporterOptionsConfigurationType.Default)
+        : this(configurationType: OtlpExporterOptionsConfigurationType.Default)
     {
     }
 
-    internal OtlpExporterOptions(
-        OtlpExporterOptionsConfigurationType configurationType)
+    internal OtlpExporterOptions(OtlpExporterOptionsConfigurationType configurationType)
         : this(
-              configuration: new ConfigurationBuilder().AddEnvironmentVariables().Build(),
-              configurationType,
-              defaultBatchOptions: new())
+            configuration: null,
+            configurationType: configurationType,
+            defaultBatchOptions: new())
     {
     }
 
     internal OtlpExporterOptions(
-        IConfiguration configuration,
+        IConfiguration? configuration,
         OtlpExporterOptionsConfigurationType configurationType,
         BatchExportActivityProcessorOptions defaultBatchOptions)
     {
         Debug.Assert(defaultBatchOptions != null, "defaultBatchOptions was null");
+        var finalConfigurationBuilder = new ConfigurationBuilder()
+            .AddEnvironmentVariables();
+
+        if (configuration != null)
+        {
+            finalConfigurationBuilder = finalConfigurationBuilder.AddConfiguration(configuration);
+        }
 
-        this.ApplyConfiguration(configuration, configurationType);
+        this.ApplyConfiguration(finalConfigurationBuilder.Build(), configurationType);
 
         this.DefaultHttpClientFactory = () =>
         {

test/OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests/OtlpExporterOptionsTests.cs

@@ -2,6 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0
 
 using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Options;
+using OpenTelemetry.Trace;
 using Xunit;
 
 namespace OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests;
@@ -164,6 +168,44 @@ public void OtlpExporterOptions_SetterOverridesEnvironmentVariable()
         Assert.False(options.AppendSignalPathToEndpoint);
     }
 
+    // https://github.com/open-telemetry/opentelemetry-dotnet/issues/6558
+    [Fact]
+    public void OtlpExporterOptions_EnvironmentVariableAppliedAfterIConfigurationBuilt()
+    {
+        var expectedEndpoint = "http://test:4317";
+        var host = Host
+            .CreateDefaultBuilder()
+            .ConfigureServices((_, services) =>
+            {
+                Environment.SetEnvironmentVariable("OTEL_EXPORTER_OTLP_ENDPOINT", expectedEndpoint);
+                services
+                    .AddOpenTelemetry()
+                    .WithTracing(builder => builder.AddOtlpExporter());
+            })
+            .Build();
+
+        var options = host.Services.GetRequiredService<IOptions<OtlpExporterOptions>>().Value;
+
+        Assert.Equal(new Uri(expectedEndpoint), options.Endpoint);
+    }
+
+    // https://github.com/open-telemetry/opentelemetry-dotnet/issues/5586
+    [Fact]
+    public void OtlpExporterOptions_EnvironmentVariableAppliedWhenEmptyApplication()
+    {
+        var expectedEndpoint = "http://test:4317";
+        Environment.SetEnvironmentVariable("OTEL_EXPORTER_OTLP_ENDPOINT", expectedEndpoint);
+        var hostBuilder = Host.CreateEmptyApplicationBuilder(settings: null);
+        hostBuilder.Services
+            .AddOpenTelemetry()
+            .WithTracing(builder => builder.AddOtlpExporter());
+        var host = hostBuilder.Build();
+
+        var options = host.Services.GetRequiredService<IOptions<OtlpExporterOptions>>().Value;
+
+        Assert.Equal(new Uri(expectedEndpoint), options.Endpoint);
+    }
+
     [Fact]
     public void OtlpExporterOptions_EndpointGetterUsesProtocolWhenNull()
     {