Add default_histogram_aggregation configuration option to prometheus exporter #4124
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carlosalberto
approved these changes
Jul 3, 2024
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cc @dashpole |
dashpole
reviewed
Jul 8, 2024
| histogram aggregation. The option MAY be named `default_histogram_aggregation`, | ||
| and MUST support the following values: | ||
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| * `explicit_bucket_histogram`: Use [Explicit Bucket Histogram Aggregation](../sdk.md#explicit-bucket-histogram-aggregation). |
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This structure makes sense for environment-variable-based config, where we expect string constants, but maybe not so much for SDK exporter config? E.g. Go allows users to provide an AggregationSelector, which I don't think would comply with this.
arminru
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jack-berg
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Jul 24, 2024
… default aggregation (#4142) Reviewing @dashpole's [comments](#4124 (review)) on #4124, I realize that a key clarification is missing for the contract between readers and exporters, and for the configuration of built-in exporters. We [state that](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#metricreader) MetricReaders should be constructed with: - "The default output aggregation (optional), a function of instrument kind. If not configured, the [default aggregation](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#default-aggregation) SHOULD be used." - "The default output temporality (optional), a function of instrument kind. If not configured, the Cumulative temporality SHOULD be used." And for MetricExporters, we [state that](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#metricexporter) "The aggregation and temporality properties used by the OpenTelemetry Metric SDK are determined when registering Metric Exporters through their associated MetricReader." But we don't connect the dots that the `aggregation` and `temporality` options for the MetricReader should be obtained from a MetricExporter. I think this is understood, since the whole reason these are configurable at the MetricReader level is that MetricExporters and their associated backends have different requirements around temporality and default aggregation (especially in the case of base2 exponential histogram). This PR clarifies that the MetricReader `aggregation` and `temporality` options SHOULD come from the associated MetricExporter, NOT from the caller. Furthermore, because these are now clearly spelled out as preferences of MetricExporter, I've updated all the built-in metric exporter definitions to make expectations clear around what defaults and configuration of `aggregation` and `temporality` should be supported. This achieves the goals of #4124 in a more generic way. | Exporter | default `aggregation` | `temporality` | |---|---|---| | Prometheus | configurable | always cumulative | | OTLP | configurable | configurable | | Standard Output | configurable | configurable | | InMemory | configurable | configurable |
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Similar to how its possible to specify that base2 exponential histogram should be the default histogram aggregation for the otlp metric exporter, it should be possible to do so for the prometheus exporter.
This adds a new optional config option to the prometheus exporter called
default_histogram_aggregation, with the same mechanics as the OTLP-exporter equivalent.The motivation is that there is a PR to extend the file configuration schema with this option, and we have a rule that all portions of the file configuration schema should be explicitly defined or implied by language in the spec, since we don't want to add configuration options which could potentially contradict the spec.
cc @open-telemetry/configuration-maintainers, @open-telemetry/wg-prometheus, @Abhishekkr3003