Remove SDK's dependency on opentelemetry-instrumentation

[owais]

Today the SDK depends on opentelemetry-instrumentation package because it needs to import opentelemetry.instrumentation.utils._SUPPRESS_INSTRUMENTATION_KEY in order to suppress instrumentation in its own exporters. We decided in last SIG call to get rid of this dependency as it does not make sense to have SDK depend on the instrumentation package and it complicates things in general.

Right now the _SUPRESS_INSTRUMENTATION variable is a an opentelemetry context key i.e, it is a randomly generated uuid. We have two options to fix this:

1. Make _SUPPRESS_INSTRUMENTATION_KEY a static symbol e.g, a well-known string value that is used by convention by SDK and opentelemetry-instrumentation both without importing it from anywhere. This is the simplest and quite robust but it technically violates the spec as context keys should not be static strings.

2. Move the _SUPRESS_INSTRUMENTATION_KEY to opentelemetry.context._SUPRESS_INSTRUMENTATION_KEY. We'll place it in the API package but it'll not be part of the public context API just like it is not a part of public instrumentation API today. It'll continue to be strictly used by internal package just like today. Both SDK and instrumention packages will import it from opentelemetry.context._SUPPRESS_INSTRUMENTATION_KEY. Once the spec recommends a way to implement this officially, we can get rid of this or make it part of the public API.

3rd options is to have SDK or instrumentation package "register" a global key like this in opentelemetry.context. namespace just like we register propagators or providers but I feel it'd be overkill for this problem. I think we should go with 2.

[codeboten]

I would support Option 2, I think the dependency on the instrumentation package is problematic.

[owais]

@open-telemetry/python-approvers @open-telemetry/python-maintainers thoughts?

[NathanielRN]

It does feel wrong to have opentelemetry-sdk depend on opentelemetry-instrumentation just for that one value, but I’ve found it really convenient to install the SDK package and get the instrumentation package for free. I think the common use case would include both, but have the requirement means the “SDK without instrumentation” cannot exist right now. So this change makes sense.

Maybe installing all these “regular use case” packages is what distros should solve.

[owais]

Each distro can solve whatever it wants :) but yes this is something that all distros would obviously want to solve.

The upcoming opentelemetry python package will also solve this problem i.e, install everything required to get started with Otel + Python