Fix use of built-in samplers in SDK configuration

CHANGELOG.md

@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#3100](https://github.com/open-telemetry/opentelemetry-python/pull/3100))
 - Fix formatting of ConsoleMetricExporter.
   ([#3197](https://github.com/open-telemetry/opentelemetry-python/pull/3197))
+- Fix use of built-in samplers in SDK configuration
+  ([#3176](https://github.com/open-telemetry/opentelemetry-python/pull/3176))
 - Implement shutdown procedure forOTLP grpc exporters
   ([#3138](https://github.com/open-telemetry/opentelemetry-python/pull/3138))
 - Add exponential histogram

opentelemetry-sdk/pyproject.toml

@@ -41,6 +41,14 @@ sdk = "opentelemetry.sdk.environment_variables"
 [project.entry-points.opentelemetry_id_generator]
 random = "opentelemetry.sdk.trace.id_generator:RandomIdGenerator"
 
+[project.entry-points.opentelemetry_traces_sampler]
+always_on = "opentelemetry.sdk.trace.sampling:_AlwaysOn"
+always_off = "opentelemetry.sdk.trace.sampling:_AlwaysOff"
+parentbased_always_on = "opentelemetry.sdk.trace.sampling:_ParentBasedAlwaysOn"
+parentbased_always_off = "opentelemetry.sdk.trace.sampling:_ParentBasedAlwaysOff"
+traceidratio = "opentelemetry.sdk.trace.sampling:TraceIdRatioBased"
+parentbased_traceidratio = "opentelemetry.sdk.trace.sampling:ParentBasedTraceIdRatio"
+
 [project.entry-points.opentelemetry_logger_provider]
 sdk_logger_provider = "opentelemetry.sdk._logs:LoggerProvider"
 

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

@@ -295,16 +295,28 @@ def _import_sampler(sampler_name: str) -> Optional[Sampler]:
         return None
     try:
         sampler_factory = _import_sampler_factory(sampler_name)
-        sampler_arg = os.getenv(OTEL_TRACES_SAMPLER_ARG, "")
-        sampler = sampler_factory(sampler_arg)
+        arg = None
+        if sampler_name in ("traceidratio", "parentbased_traceidratio"):
+            try:
+                rate = float(os.getenv(OTEL_TRACES_SAMPLER_ARG))
+            except (ValueError, TypeError):
+                _logger.warning(
+                    "Could not convert TRACES_SAMPLER_ARG to float. Using default value 1.0."
+                )
+                rate = 1.0
+            arg = rate
+        else:
+            arg = os.getenv(OTEL_TRACES_SAMPLER_ARG)
+
+        sampler = sampler_factory(arg)
         if not isinstance(sampler, Sampler):
             message = f"Sampler factory, {sampler_factory}, produced output, {sampler}, which is not a Sampler."
             _logger.warning(message)
             raise ValueError(message)
         return sampler
     except Exception as exc:  # pylint: disable=broad-except
         _logger.warning(
-            "Using default sampler. Failed to initialize custom sampler, %s: %s",
+            "Using default sampler. Failed to initialize sampler, %s: %s",
             sampler_name,
             exc,
         )

opentelemetry-sdk/src/opentelemetry/sdk/trace/sampling.py

@@ -394,6 +394,26 @@ def __init__(self, rate: float):
         super().__init__(root=root)
 
 
+class _AlwaysOff(StaticSampler):
+    def __init__(self, _):
+        super().__init__(Decision.DROP)
+
+
+class _AlwaysOn(StaticSampler):
+    def __init__(self, _):
+        super().__init__(Decision.RECORD_AND_SAMPLE)
+
+
+class _ParentBasedAlwaysOff(ParentBased):
+    def __init__(self, _):
+        super().__init__(ALWAYS_OFF)
+
+
+class _ParentBasedAlwaysOn(ParentBased):
+    def __init__(self, _):
+        super().__init__(ALWAYS_ON)
+
+
 _KNOWN_SAMPLERS = {
     "always_on": ALWAYS_ON,
     "always_off": ALWAYS_OFF,
@@ -415,7 +435,7 @@ def _get_from_env_or_default() -> Sampler:
     if trace_sampler in ("traceidratio", "parentbased_traceidratio"):
         try:
             rate = float(os.getenv(OTEL_TRACES_SAMPLER_ARG))
-        except ValueError:
+        except (ValueError, TypeError):
             _logger.warning("Could not convert TRACES_SAMPLER_ARG to float.")
             rate = 1.0
         return _KNOWN_SAMPLERS[trace_sampler](rate)