Honor OTEL_RESOURCE_ATTRIBUTES environment variable

[zakimaksyutov]

In my Kubernetes setup every pod gets OTEL_RESOURCE_ATTRIBUTES environment variable set which contains everything needed to troubleshoot/monitor our microservices. Every app instrumented with Open Telemetry automatically picks up these resource attributes. But Nginx does not. As a result, through it emits spans and participated in distributed tracing, it doesn't contain everything.

Describe the solution you'd like

nginx-otel module to honor OTEL_RESOURCE_ATTRIBUTES environment variable and emits them as Resource object.

According to Open Telemetry spec, all producers must honor this environment variable.

Describe alternatives you've considered

The closest - with otel_span_attr it is potentially possible to inject needed information as span attribute. But this still will not be resource attribute and as a result not aligned with the rest of applications. This also will require nginx.conf changes every time we decide to add something to OTEL_RESOURCE_ATTRIBUTES.

[p-pautov]

There is #32 to support custom resource attributes via config, but supporting environment variables like OTEL_RESOURCE_ATTRIBUTES and OTEL_SERVICE_NAME makes sense as well.

[JPeer264]

It would also be nice to have the exporter (OTEL_EXPORTER_OTLP_ENDPOINT) and its headers (OTEL_EXPORTER_OTLP_HEADERS) to be configurable via environment variables: https://opentelemetry.io/docs/languages/sdk-configuration/otlp-exporter/.

[codemonkeynumber24]

With the implementation of #32 the basic use case this solves is implemented, but it would be a real quality of life upgrade if the env vars could also be used to instrument nginx.
Is there any chance of this happening?

[p-pautov]

I think, we'll eventually support some subset of OTel environment variables. Are interested in some specific vars?

[codemonkeynumber24]

Thanks for your consideration, as mentioned by @JPeer264 it would be quite useful to be able to use env vars to set manage the endpoint and to handle auth, so OTEL_EXPORTER_OTLP_ENDPOINT and OTEL_EXPORTER_OTLP_HEADERS would be good to have, even better if there is more granular control with the vars OTEL_EXPORTER_OTLP_METRICS_ENDPOINT, OTEL_EXPORTER_OTLP_LOGS_ENDPOINT and OTEL_EXPORTER_OTLP_TRACES_ENDPOINT.
Similar granularity with respect to auth would be good also, but not as widely used I imagine.
Since the primary usecase for the env vars is to handle differences between deployment environments, things that may be identical across different environments would not be as critical to handle via env vars.
The only other var that comes to mind would be OTEL_RESOURCE_ATTRIBUTES, everything else can be added in at buildtime.