Fix use of built-in samplers in SDK configuration

[matej-g]

Description

Fixes a configuration bug which causes the instrumentation to fall back on the default sampler when a built-in sampler is specified, due to the samplers missing from entry points. For details see description of #3175.

P.S. I'm not a Python developer, so feedback on if this should be done other way is welcome.

Fixes #3175

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Existing unit tests
• Reproduced the scenario described in Setting built-in sampler with auto-instrumentation fails with Failed to initialize custom sampler due to it missing from entry points #3175 with expected behavior

Does This PR Require a Contrib Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[ocelotl]

Added a question

[matej-g]

Hi @srikanthccv, sorry for the back and forth, I implemented it with your suggestion and cleaned up the PR. Hopefully now all is as should be.

[srikanthccv]

Thanks @matej-g , but the type conversion is also missing here

opentelemetry-python/opentelemetry-sdk/src/opentelemetry/sdk/_configuration/__init__.py

Lines 298 to 299 in f05fa77

	sampler_arg = os.getenv(OTEL_TRACES_SAMPLER_ARG, "")
	sampler = sampler_factory(sampler_arg)

This is an existing bug, let me know if you want to make the change in this PR otherwise I will get it fixed separately and then merge this.

It should be changed to

sampler_factory = _import_sampler_factory(sampler_name)

kwargs = {}
if sampler_name in ("traceidratio", "parentbased_traceidratio"):
    try:
        rate = float(os.getenv(OTEL_TRACES_SAMPLER_ARG))
    except ValueError:
        _logger.warning("Could not convert TRACES_SAMPLER_ARG to float.")
        rate = 1.0
    kwargs["rate"] = rate

sampler = sampler_factory(**kwargs)

[matej-g]

@srikanthccv you're right, that part was still missing. I added your suggestion. Hopefully now everything is fixed as expected.

[srikanthccv]

Thank you

[dnshio]

Hi. Thanks for this fix. Do you know when this fix will be available on PyPI?

[srikanthccv]

most probably (early) next week based on our monthly release schedule.

[dnshio]

most probably (early) next week based on our monthly release schedule.

Thanks @srikanthccv 🙌🏽