[bug] `EnvironmentVariableDetector` does not load variables when configured within `HostBuilder`

[maciejaszyk]

Package

OpenTelemetry

Package Version

Package Name	Version
OpenTelemetry.Api	1.14.0

Runtime Version

net8.0, net10.0

Description

The default ResourceBuilder adds EnvironmentVariableDetector, which should add resource attributes from environment variables (such as OTEL_RESOURCE_ATTRIBUTES). However, when OpenTelemetry is configured within a HostBuilder, these environment variables are ignored.

The issue appears to be located here:

opentelemetry-dotnet/src/OpenTelemetry/Resources/ResourceBuilderExtensions.cs

Lines 118 to 123 in 58519b7

	Lazy<IConfiguration> configuration = new Lazy<IConfiguration>(() => new ConfigurationBuilder().AddEnvironmentVariables().Build());
	#pragma warning disable CA1062 // Validate arguments of public methods - needed for netstandard2.1
	return resourceBuilder
	#pragma warning restore CA1062 // Validate arguments of public methods - needed for netstandard2.1
	.AddDetectorInternal(sp => new OtelEnvResourceDetector(sp?.GetService<IConfiguration>() ?? configuration.Value))

sp?.GetService<IConfiguration>() will return a value and

         Lazy<IConfiguration> configuration = new Lazy<IConfiguration>(() => new ConfigurationBuilder().AddEnvironmentVariables().Build()); 

will not be evaluated.

Steps to Reproduce

   [Fact]
    public void OTelAttributesAreAddedToTheMeterProvider()
    {
        Environment.SetEnvironmentVariable("OTEL_RESOURCE_ATTRIBUTES", "mycustom=test,other=test");

        var builder = new HostBuilder()
            .ConfigureAppConfiguration(builder =>
            {
                builder.AddInMemoryCollection(new Dictionary<string, string?>
                {
                    ["SomeUnrelatedKey"] = "SomeUnrelatedValue",
                });
            })
            .ConfigureServices(services =>
            {
                services.AddOpenTelemetry()
                    .WithMetrics(builder =>
                    {
                        var resources = ResourceBuilder.CreateDefault();
                        resources.AddService("test", "namespace", "version", false, "my_instance");
                        var attributes = resources.Build().Attributes.ToArray();
                        Assert.Contains(new KeyValuePair<string, object>("service.name", "test"), attributes);
                        Assert.Contains(new KeyValuePair<string, object>("mycustom", "test"), attributes);
                        Assert.Contains(new KeyValuePair<string, object>("other", "test"), attributes);
                        builder.SetResourceBuilder(resources);
                    });
            });

        using var host = builder.Build();
        var meterProvider = host.Services.GetRequiredService<MeterProvider>();
        Assert.IsType<MeterProviderSdk>(meterProvider);
        var attributes = ((MeterProviderSdk)meterProvider).Resource.Attributes.ToArray();
        Assert.Contains(new KeyValuePair<string, object>("service.name", "test"), attributes);
        Assert.Contains(new KeyValuePair<string, object>("mycustom", "test"), attributes);
        Assert.Contains(new KeyValuePair<string, object>("other", "test"), attributes);
    }

Assert.Contains() Failure: Item not found in collection
Collection: [["service.name"] = "test", ["service.namespace"] = "namespace", ["service.version"] = "version", ["service.instance.id"] = "my_instance", ["telemetry.sdk.name"] = "opentelemetry", ···]
Not found:  ["mycustom"] = "test"

Expected Result

I expect the attributes from OTEL_RESOURCE_ATTRIBUTES to be added to the resource attributes.

Actual Result

Environment variables are not loaded into the MeterProvider.

Additional Context

No response

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[rajkumar-rangaraj]

To help us investigate and reproduce the problem, could you please provide minimal reproduction code - A small, complete code example that demonstrates the issue.

[rajkumar-rangaraj]

The test appears to be incorrect. When you call Environment.SetEnvironmentVariable(), it doesn't retroactively add that variable to an IConfiguration that has already been built.

In your example:

Environment.SetEnvironmentVariable("OTEL_RESOURCE_ATTRIBUTES", "mycustom=test,other=test");

var builder = new HostBuilder()
    .ConfigureAppConfiguration(builder =>
    {
        builder.AddInMemoryCollection(new Dictionary<string, string?>
        {
            ["SomeUnrelatedKey"] = "SomeUnrelatedValue",
        });
    })

The ConfigureAppConfiguration only adds an in-memory collection and does not include environment variables as a configuration source. When HostBuilder builds the configuration, it won't contain OTEL_RESOURCE_ATTRIBUTES because you didn't call builder.AddEnvironmentVariables().

If you want environment variables to be available in IConfiguration, you need to explicitly add them:

.ConfigureAppConfiguration(builder =>
{
    builder.AddEnvironmentVariables(); // Add this
    builder.AddInMemoryCollection(...);
})

Could you please clarify:

What is the actual scenario you're trying to solve?
Is there a real-world use case where EnvironmentVariableDetector is not working as expected?
If so, could you provide a minimal reproduction that shows the actual problem?

Also, I recommend you to review #5586

[arekpalinski]

@rajkumar-rangaraj thanks for looking into this. I’m jumping in to provide some context on behalf of my colleague.

The core issue we are addressing is here: ravendb/ravendb#21964. The test case originally provided is a minimal reproduction designed to isolate the bug, while the linked issue describes the full real-world scenario.