Select histogram aggregation with environment variables

[ocelotl]

Fixes #3264

[srikanthccv]

I wouldn't put any OTLP exporter specific implementation in metrics SDK. The default aggregation from SDK should return the default irrespective of this env, and it should only be considered when the used exporter is OTLP. Each metric exporter has the option to configure the preferred aggregation and temporality. And I believe this logic should go in OTLP metrics exporters, similar to OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE

opentelemetry-python/exporter/opentelemetry-exporter-otlp-proto-grpc/src/opentelemetry/exporter/otlp/proto/grpc/metric_exporter/__init__.py

Lines 137 to 185 in e003062

	otel_exporter_otlp_metrics_temporality_preference = (
	environ.get(
	OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE,
	"CUMULATIVE",
	)
	.upper()
	.strip()
	)
	if otel_exporter_otlp_metrics_temporality_preference == "DELTA":
	instrument_class_temporality = {
	Counter: AggregationTemporality.DELTA,
	UpDownCounter: AggregationTemporality.CUMULATIVE,
	Histogram: AggregationTemporality.DELTA,
	ObservableCounter: AggregationTemporality.DELTA,
	ObservableUpDownCounter: AggregationTemporality.CUMULATIVE,
	ObservableGauge: AggregationTemporality.CUMULATIVE,
	}
	elif otel_exporter_otlp_metrics_temporality_preference == "LOWMEMORY":
	instrument_class_temporality = {
	Counter: AggregationTemporality.DELTA,
	UpDownCounter: AggregationTemporality.CUMULATIVE,
	Histogram: AggregationTemporality.DELTA,
	ObservableCounter: AggregationTemporality.CUMULATIVE,
	ObservableUpDownCounter: AggregationTemporality.CUMULATIVE,
	ObservableGauge: AggregationTemporality.CUMULATIVE,
	}
	else:
	if otel_exporter_otlp_metrics_temporality_preference != (
	"CUMULATIVE"
	):
	_logger.warning(
	"Unrecognized OTEL_EXPORTER_METRICS_TEMPORALITY_PREFERENCE"
	" value found: "
	f"{otel_exporter_otlp_metrics_temporality_preference}, "
	"using CUMULATIVE"
	)
	instrument_class_temporality = {
	Counter: AggregationTemporality.CUMULATIVE,
	UpDownCounter: AggregationTemporality.CUMULATIVE,
	Histogram: AggregationTemporality.CUMULATIVE,
	ObservableCounter: AggregationTemporality.CUMULATIVE,
	ObservableUpDownCounter: AggregationTemporality.CUMULATIVE,
	ObservableGauge: AggregationTemporality.CUMULATIVE,
	}
	instrument_class_temporality.update(preferred_temporality or {})

.

[srikanthccv]

See above comment

[ocelotl]

@srikanthccv moved this feature to the exporter, PTAL.