Add a simple way to configure system-metrics from outside

[xrmx]

Is your feature request related to a problem?

I would like to easily provide a different config for system metrics, i.e. to provide a subset of metrics, depending on an environment variable.

The instrumentation config can be passed to the instrumentation constructor.

Here's the config:
https://github.com/open-telemetry/opentelemetry-python-contrib/blob/main/instrumentation/opentelemetry-instrumentation-system-metrics/src/opentelemetry/instrumentation/system_metrics/__init__.py#L99

In today SIG @aabmass suggested to take a look at BaseDistro.load_instrumentor() that may already do the trick

Describe the solution you'd like

No solution in mind

Describe alternatives you've considered

None

Additional context

[xrmx]

cc @jeremydvoss

[xrmx]

So using load_instrumentor will look like this:

diff --git a/src/elasticotel/distro/__init__.py b/src/elasticotel/distro/__init__.py
index ef1bd6a..60816fa 100644
--- a/src/elasticotel/distro/__init__.py
+++ b/src/elasticotel/distro/__init__.py
@@ -19,11 +19,14 @@ from opentelemetry.environment_variables import (
     OTEL_TRACES_EXPORTER,
 )
 from opentelemetry.instrumentation.distro import BaseDistro
+from opentelemetry.instrumentation.instrumentor import BaseInstrumentor
+from opentelemetry.instrumentation.system_metrics import _DEFAULT_CONFIG, SystemMetricsInstrumentor
 from opentelemetry.sdk._configuration import _OTelSDKConfigurator
 from opentelemetry.sdk.environment_variables import (
     OTEL_EXPERIMENTAL_RESOURCE_DETECTORS,
     OTEL_EXPORTER_OTLP_PROTOCOL,
 )
+from pkg_resources import EntryPoint
 
 
 class ElasticOpenTelemetryConfigurator(_OTelSDKConfigurator):
@@ -31,6 +34,14 @@ class ElasticOpenTelemetryConfigurator(_OTelSDKConfigurator):
 
 
 class ElasticOpenTelemetryDistro(BaseDistro):
+    def load_instrumentor(self, entry_point: EntryPoint, **kwargs):
+
+        instrumentor_class: BaseInstrumentor = entry_point.load()
+        instrumentor_kwargs = {}
+        if instrumentor_class == SystemMetricsInstrumentor:
+            instrumentor_kwargs["config"] = {k: v for k, v in _DEFAULT_CONFIG.items() if k.startswith("process.runtime")}
+        instrumentor_class(**instrumentor_kwargs).instrument(**kwargs)
+
     def _configure(self, **kwargs):
         os.environ.setdefault(OTEL_TRACES_EXPORTER, "otlp")
         os.environ.setdefault(OTEL_METRICS_EXPORTER, "otlp")

An improvement would be to being able to reduce a bit of duplicated code would be something like this where on the distro side I would only override the helper returning the kwargs for the instrumentor constructor:

diff --git a/opentelemetry-instrumentation/src/opentelemetry/instrumentation/distro.py b/opentelemetry-instrumentation/src/opentelemetry/instrumentation/distro.py
index 93646bbb..02fa3b8d 100644
--- a/opentelemetry-instrumentation/src/opentelemetry/instrumentation/distro.py
+++ b/opentelemetry-instrumentation/src/opentelemetry/instrumentation/distro.py
@@ -47,6 +47,11 @@ class BaseDistro(ABC):
         """Configure the distribution"""
         self._configure(**kwargs)
 
+    def load_instrumentor_kwargs(self, instrumentor: BaseInstrumentor) -> dict:
+        """Takes an instrumentor class and returns a dict of kwargs to pass to
+        the constructor"""
+        return {}
+
     def load_instrumentor(  # pylint: disable=no-self-use
         self, entry_point: EntryPoint, **kwargs
     ):
@@ -61,6 +66,7 @@ class BaseDistro(ABC):
         skip loading entirely, etc.
         """
         instrumentor: BaseInstrumentor = entry_point.load()
-        instrumentor().instrument(**kwargs)
+       instrumentor_kwargs = self.load_instrumentor_kwargs(instrumentor)
+       instrumentor(**instrumentor_kwargs).instrument(**kwargs)
 

[jeremydvoss]

load_instrumentor_kwargs seems to me like a method that can be entirely handled by the custom ElasticOpenTelemetryDistro. I think we should only change the sdk/api if it were preventing instrumentation kwarg configuration

[xrmx]

Would making it an internal helper ok? It would be useful as documentation at least.