protocol/exporter: Configuration options MAY be implemented by exporter, SDK, or separate component

[pellared]

Fixes #3721

Why

The Go SIG is working towards stabilizing the OTLP metrics exporter.

The Go SIG would prefer to manage the exporter environment variables through a distinct package: https://pkg.go.dev/go.opentelemetry.io/contrib/exporters/autoexport. This approach is akin to Java Autoconfigure. The rationale behind this decision is as follows:

1. If users aim to utilize the OTEL_EXPORTER_OTLP_PROTOCOL and OTEL_TRACES_EXPORTER, we aim to support all the values documented in the specification. We want to ensure that users are not prone to encountering runtime errors if a protocol driver hasn't been registered in the code.
2. Simultaneously, we wish to avoid applications to depend on all exporter implementations defined in the specification.

Currently, it is not clear of such design is in compliance with the specification.

What

Define that configuration options MAY be implemented by exporter, SDK, or separate component.

While this PR may be seen as a breaking change, because of the way how the languages adopted the specification I would say that this is a "clarification" or "adopting to the reality".

Here is how different languages currently implement the OTLP configuration options.

.NET

Configuration options implemented by exporter.
Side note: Per-signal endpoint configuration options are not implemented.

Source code:

• https://github.com/open-telemetry/opentelemetry-dotnet/tree/main/src/OpenTelemetry.Exporter.OpenTelemetryProtocol

C++

Most configuration options implemented by exporter.
However, the *_PROTOCOL env vars are not implemented at all. See: open-telemetry/opentelemetry-cpp#971.

Source code:

• https://github.com/open-telemetry/opentelemetry-cpp/tree/main/exporters/otlp

Erlang

Configuration options implemented by exporter.

Source code:

• https://github.com/open-telemetry/opentelemetry-erlang/tree/main/apps/opentelemetry_exporter

Go

Most configuration options implemented by exporter.
However, the *_PROTOCOL env vars are implemented by a separate component (autoexport)

Source code (package docs):

• https://pkg.go.dev/go.opentelemetry.io/contrib/exporters/autoexport
• https://pkg.go.dev/go.opentelemetry.io/otel/exporters/otlp/otlptrace

Java

Configuration options implemented by an autoconfigure component.

Source code:

• https://github.com/open-telemetry/opentelemetry-java/tree/main/sdk-extensions/autoconfigure
• https://github.com/open-telemetry/opentelemetry-java/tree/main/exporters/otlp/all/src/main/java/io/opentelemetry/exporter/otlp

JavaScript

Most configuration options implemented by exporter.
However, the *_PROTOCOL env vars are implemented by a separate component (opentelemetry-sdk-node)

Source code:

• https://github.com/open-telemetry/opentelemetry-js/tree/main/experimental/packages/opentelemetry-sdk-node
• https://github.com/open-telemetry/opentelemetry-js/tree/main/experimental/packages/exporter-trace-otlp-http

PHP

Configuration options implemented by exporter.

Source code:

• https://github.com/open-telemetry/opentelemetry-php/tree/main/src/Contrib/Otlp

Python

Most configuration options implemented by exporter.
However, the *_PROTOCOL env vars are implemented by the SDK.

Source code:

• https://github.com/open-telemetry/opentelemetry-python/blob/main/opentelemetry-sdk/src/opentelemetry/sdk/_configuration/__init__.py
• https://github.com/open-telemetry/opentelemetry-python/tree/main/exporter

Ruby

Most configuration options implemented by exporter.
However, the *_PROTOCOL env vars are implemented by the SDK.

Source code:

• https://github.com/open-telemetry/opentelemetry-ruby/blob/main/sdk/lib/opentelemetry/sdk/configurator.rb
• https://github.com/open-telemetry/opentelemetry-ruby/tree/main/exporter/otlp-http

Rust

Configuration options implemented by exporter.

Source code:

• https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry-otlp

Swift

Env vars not supported.

Previous work and discussions

• Clarify if the OTLP exporter has to support all protocol related env vars #3721
• Define OTLP protocol driver registration mechanism #3722

[tigrannajaryan]

This is a clarification/guidance, not a breaking change. LGTM.

[carlosalberto]

Let's mention this PR at the maintainers meeting today, and unless we get a complain, let's merge today.

[pellared]

I created #3738 which may supersede this PR.

However, I would prefer to merge this one first. I can remove the changes from this PR as part of #3738. I feel that #3738 may need more time for reviews and refinements.