fix histogram metrics in OTLP (#2564)

Fix #2493

with the inexpensive selector, histogram are only reported as gauges,
and so they will be incorrectly interpreted when reaching Datadog

.changesets/fix_geal_fix_datadog_histograms.md

@@ -0,0 +1,5 @@
+### Fix histograms metrics in OTLP ([Issue #2393](https://github.com/apollographql/router/issues/2493))
+
+with the "inexpensive" metrics selector, histogram are only reported as gauges, and so they will be incorrectly interpreted when reaching Datadog
+
+By [@GEal](https://github.com/geal) in https://github.com/apollographql/router/pull/2564

apollo-router/src/plugins/telemetry/metrics/otlp.rs

@@ -1,4 +1,5 @@
 use opentelemetry::sdk::export::metrics::aggregation;
+use opentelemetry::sdk::metrics::selectors;
 use opentelemetry::sdk::Resource;
 use opentelemetry::KeyValue;
 use opentelemetry_otlp::HttpExporterBuilder;
@@ -41,7 +42,9 @@ impl MetricsConfigurator for super::super::otlp::Config {
             Some(exporter) => {
                 let exporter = opentelemetry_otlp::new_pipeline()
                     .metrics(
-                        opentelemetry::sdk::metrics::selectors::simple::inexpensive(),
+                        selectors::simple::histogram([
+                            0.001, 0.005, 0.015, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 5.0, 10.0,
+                        ]),
                         aggregation::stateless_temporality_selector(),
                         opentelemetry::runtime::Tokio,
                     )