Support Environment Variable Installation and Configuration of Jaeger Remote Sampler

[pwinters-tanium]

Problem Statement

The jaeger remote sampler does not currently support auto installation or configuration using the standard OTEL_TRACES_SAMPLER and OTEL_TRACES_SAMPLER_ARG environment variables (see Environment Variable Specification). Although this is not explicitly required by Otel specifications, it is a common practice that allows an application's tracing to be configured for different contexts without recompilation.

Proposed Solution

The OTel golang SDK should automatically use the jaeger remote sampler when OTEL_TRACES_SAMPLER equals jaeger_remote.

The installed Jaeger Remote Sampler should use configuration values drawn by parsing OTEL_TRACES_SAMPLER_ARG as a comma separated list of key=value pairs that include keys endpoint, pollingIntervalMs, and initialSamplingRate.

For jaeger_remote and parentbased_jaeger_remote: The value [of OTEL_TRACES_SAMPLER_ARG] is a comma separated list:

• endpoint: the endpoint in form of scheme://host:port of gRPC server that serves the sampling strategy for the service (sampling.proto).
• pollingIntervalMs: in milliseconds indicating how often the sampler will poll the backend for updates to sampling strategy.
• initialSamplingRate: in the [0..1] range, which is used as the sampling probability when the backend cannot be reached to retrieve a sampling strategy. This value stops having an effect once a sampling strategy is retrieved successfully, as the remote strategy will be used until a new update is retrieved.

Example: endpoint=http://localhost:14250,pollingIntervalMs=5000,initialSamplingRate=0.25

Reference: Docs - Specs - OTel 1.38.0 - Configuration - Env var