`WithEnvironment` does not override actual environment variable in runtime

[kcadduk]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Setting the OTEL endpoint via WithEnvironment is reflected in the Aspire Dashboard, but the application ignores it at runtime. For example:

builder.AddProject<Api>("weather-api") .WithEnvironment("OTEL_EXPORTER_OTLP_ENDPOINT","http://localhost:4317");

Dashboard shows http://localhost:4317 for OTEL_EXPORTER_OTLP_ENDPOINT

Runtime actually uses a different endpoint like http://localhost:62312

This prevents redirecting traces to a custom OTEL collector.

Notes:

I have not called AddOpenTelemetryCollector(...), per previous feedback (#11298) that WithEnvironment should suffice. It's not needed to reproduce the problem. However if used, the behaviour is exactly the same.

The discrepancy is between what Aspire reports and the actual environment in the running app.

Repo for reproduction: AspireOtelDemo

Expected Behavior

WithEnvironment should respect the configured OTEL endpoint

Steps To Reproduce

As Above

Exceptions (if any)

None

.NET Version info

9 & 10

Anything else?

None

[karolz-ms]

@kcadduk does this happen with any other environment variable? Like, if you do WithEnvironment("MY_FANTASTIC_VAR", 42) -- is MY_FANTASTIC_VAR correctly set for the program?

[kcadduk]

So after realising that a colleague had included the wrong OTEL Integration package. It did successfully override the variable at run time after adding AddOpenTelemetryCollector. But based on the description of the other issue, this should work, regardless of whether you use the AddOpenTelemetryCollector method call or not.

@karolz-ms I understand that your scenario works. It is just this environment variable that is rather picky. I will test again and confirm however.

[karolz-ms]

I looked a bit more closely at this recently and there is simply no great way currently in Aspire model to override OTEL endpoint variable. It is set automatically based on configuration parameters (specifically, Aspire dashboard OTEL endpoint, see https://github.com/dotnet/aspire/blob/main/src/Shared/OtlpEndpointResolver.cs#L23).

This happens pretty late in the application startup sequence, so even if the application host code tries to set the value of this vairable via WithEnvironment(), it gets overridden. 😑