Add OTEL_EXPORTER environment variable

[trask]

Fixes #710

Changes

Adds OTEL_EXPORTER environment variable to select the exporter to be used.

Adds OTEL_EXPORTER_OTLP_ENDPOINT environment variable to configure the ingest endpoint for both OTLP spans and metrics.

Notes

1. I added OTEL_EXPORTER_OTLP_ENDPOINT in this PR because I think it makes the default value OTEL_EXPORTER=otlp make more sense.

   (It also happens to be the env var that the Java SDK uses currently, and seems simpler for most OTLP users, who will be sending spans and metrics to the same endpoint)

   An alternative would be to specify the default value as OTEL_EXPORTER=otlp_span,otlp_metric.

2. I went with the singular OTEL_EXPORTER over the plural OTEL_EXPORTERS, since the common use case is to configure just one exporter and so this seems less confusing.

[codeboten]

Is there a mention in the spec as to what the known values that should be used to identify exporters are and how exporters should register these values? That would be useful for anyone implementing additional exporters.

[SergeyKanzhelev]

Adds OTEL_EXPORTER environment variable to select the exporter to be used.

would it make more sense for every exporter to keep _ENABLED variable (like OTEL_EXPORTER_OTLP_SPAN_ENABELD and OTEL_EXPORTER_JAEGER_ENABLED)? This way we can enable any number of exporters and no need to keep the centralized list. Also it is more extensible as the list of exporters can be extended in very logical way.

Having OTEL_EXPORTER is more aligned with the existence of a single batch processor setting. But I'd argue it's more logical to have enable flag configured with the exporter.

[trask]

There are two alternatives suggested above. I like both of them, except around handling of the default value.

1. Suggestion: split into two env vars, one for span exporter (OTEL_EXPORTER_SPAN) and one for metric exporter (OTEL_EXPORTER_METRIC)

   The default in this case would be OTEL_EXPORTER_SPAN=otlp and OTEL_EXPORTER_METRIC=otlp.

   If someone wants to use jaeger, would they need to set both OTEL_EXPORTER_SPAN=jaeger and OTEL_EXPORTER_METRIC=none?

2. Suggestion: split out into a boolean flag for each exporter (OTEL_EXPORTER_*_ENABLED)

   The default in this case would be OTEL_EXPORTER_OTLP_ENABLED=true and all others OTEL_EXPORTER_*_ENABLED=false.

   If someone wants to use jaeger, would they need to set both OTEL_EXPORTER_JAEGER_ENABLED=true and OTEL_EXPORTER_OTLP_ENABLED=false.

Wondering if anyone has suggestions how to handle default value better in either of these cases? Or should we stick with the single environment variable OTEL_EXPORTER with default value otlp?

[iNikem]

I prefer the third alternative, which is currently written in PR :)

[trask]

In case we go with OTEL_EXPORTER, and because I ❤️ naming, does anyone care between:

• OTEL_EXPORTER=otlp_span
• OTEL_EXPORTER=otlp-span
• OTEL_EXPORTER=otlpspan

Exporter names seem sort of like propagator names, not sure if there's any convention we can follow from those?

[iNikem]

For some reason OTEL_EXPORTER=otlp_span seems the most natural to me

[SergeyKanzhelev]

@trask you got me on default values. Single variable is better from this perspective.

As for naming, I again tend to lean to separate variables for metrics and spans. It feels like two separate pieces of configuration semantically.

Since I also ❤️ naming, should we get PM to this PR to help nail the desired semantic of this config settings ;-)?

(edit: I assumed "because I ❤️ naming" was a sarcasm. If not, than mine is =))

[codeboten]

Thanks for the updates, this LGTM

[trask]

(edit: I assumed "because I ❤️ naming" was a sarcasm. If not, than mine is =))

Mine was intentionally ambiguous 😂. I have a complicated relationship with naming.

[tigrannajaryan]

LGTM

[SergeyKanzhelev]

Last edit was a day ago, so plan to merge tomorrow morning unless somebody will comment with blocking concerns

[owais]

Other than OTLP, most other exporters expect an explicit value for "service name". OTLP expects a service_name resource attribute. The spec already specifies a way to configure resource attributes globally for a service using environment variables (OTEL_RESOURCE_ATTRIBUTES) so OTLP is covered but this leaves other exporters without a way to set the service name. We can either add a common OTEL_SERVICE_NAME env var or one env var per exporter like OTEL_EXPORTER_JAEGER_SERVICE_NAME.

[trask]

We can either add a common OTEL_SERVICE_NAME env var or one env var per exporter like OTEL_EXPORTER_JAEGER_SERVICE_NAME.

Hey @owais, check out (and vote for!) #709