malff@localhost.localdomain:otlp> pwd
/home/malff/CODE/MARC_GITHUB/build-otelcpp-2/examples/otlp
malff@localhost.localdomain:otlp> env | grep OTLP
OTEL_EXPORTER_OTLP_TRACES_ENDPOINT=POISON
malff@localhost.localdomain:otlp> ./example_otlp_metric_grpc
[Error] File: /home/malff/CODE/MARC_GITHUB/opentelemetry-cpp/exporters/otlp/src/otlp_grpc_metric_exporter.cc:75[OTLP METRIC GRPC Exporter] Export() failed: DNS resolution failed for POISON:80: C-ares status is not ARES_SUCCESS qtype=AAAA name=POISON is_balancer=0: Domain name not found

Here, example_otlp_metric_grpc is expected to use environment variable OTEL_EXPORTER_OTLP_METRICS_ENDPOINT.

Instead, it uses environment variable OTEL_EXPORTER_OTLP_TRACES_ENDPOINT, as proven with the poisoned value set.

The root cause is:

struct OtlpGrpcMetricExporterOptions : public OtlpGrpcExporterOptions

While this sounds like code reuse at first read, this inheritance is flawed:

• OtlpGrpcExporterOptions is poorly named, it is dedicated to the trace signal
• the constructor for OtlpGrpcMetricExporterOptions will lookup _TRACES_ environment variables, instead of _METRICS_

Logs are also affected:

OtlpGrpcLogRecordExporterFactory::Create(
      const OtlpGrpcExporterOptions &options)

The options passed should be specific to the log signal, here the trace options are used instead.

OtlpGrpcExporterOptions should really be renamed to avoid causing confusion here.