feat(telemetry): add configurable histogram buckets for metrics

.changesets/feat_swan_cub_foot_audience.md

@@ -0,0 +1,21 @@
+### Configurable histogram buckets for metrics ([Issue #2333](https://github.com/apollographql/router/issues/2333))
+
+You can customize the buckets for all generated histograms:
+
+```yaml title="router.yaml"
+telemetry:
+  metrics:
+    common:
+      buckets:
+        - 0.05
+        - 0.10
+        - 0.25
+        - 0.50
+        - 1.00
+        - 2.50
+        - 5.00
+        - 10.00
+        - 20.00
+```
+
+By [@bnjjj](https://github.com/bnjjj) in https://github.com/apollographql/router/pull/3098

apollo-router/src/configuration/snapshots/apollo_router__configuration__tests__schema_generation.snap

@@ -3711,6 +3711,28 @@ expression: "&schema"
                   "additionalProperties": false,
                   "nullable": true
                 },
+                "buckets": {
+                  "description": "Custom buckets for histograms",
+                  "default": [
+                    0.001,
+                    0.005,
+                    0.015,
+                    0.05,
+                    0.1,
+                    0.2,
+                    0.3,
+                    0.4,
+                    0.5,
+                    1.0,
+                    5.0,
+                    10.0
+                  ],
+                  "type": "array",
+                  "items": {
+                    "type": "number",
+                    "format": "double"
+                  }
+                },
                 "resources": {
                   "description": "Resources",
                   "default": {},
@@ -3721,11 +3743,13 @@ expression: "&schema"
                 },
                 "service_name": {
                   "description": "Set a service.name resource in your metrics",
+                  "default": null,
                   "type": "string",
                   "nullable": true
                 },
                 "service_namespace": {
                   "description": "Set a service.namespace attribute in your metrics",
+                  "default": null,
                   "type": "string",
                   "nullable": true
                 }

apollo-router/src/plugins/telemetry/config.rs

@@ -80,17 +80,25 @@ pub(crate) struct Metrics {
 }
 
 #[derive(Clone, Default, Debug, Deserialize, JsonSchema)]
-#[serde(deny_unknown_fields, rename_all = "snake_case")]
+#[serde(deny_unknown_fields, rename_all = "snake_case", default)]
 pub(crate) struct MetricsCommon {
     /// Configuration to add custom labels/attributes to metrics
     pub(crate) attributes: Option<MetricsAttributesConf>,
     /// Set a service.name resource in your metrics
     pub(crate) service_name: Option<String>,
     /// Set a service.namespace attribute in your metrics
     pub(crate) service_namespace: Option<String>,
-    #[serde(default)]
     /// Resources
     pub(crate) resources: HashMap<String, String>,
+    /// Custom buckets for histograms
+    #[serde(default = "default_buckets")]
+    pub(crate) buckets: Vec<f64>,
+}
+
+fn default_buckets() -> Vec<f64> {
+    vec![
+        0.001, 0.005, 0.015, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 5.0, 10.0,
+    ]
 }
 
 /// Tracing configuration

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

@@ -42,9 +42,7 @@ impl MetricsConfigurator for super::super::otlp::Config {
             Some(exporter) => {
                 let exporter = opentelemetry_otlp::new_pipeline()
                     .metrics(
-                        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,
-                        ]),
+                        selectors::simple::histogram(metrics_config.buckets.clone()),
                         aggregation::stateless_temporality_selector(),
                         opentelemetry::runtime::Tokio,
                     )

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

@@ -85,9 +85,7 @@ impl MetricsConfigurator for Config {
         if self.enabled {
             let mut controller = controllers::basic(
                 processors::factory(
-                    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,
-                    ]),
+                    selectors::simple::histogram(metrics_config.buckets.clone()),
                     aggregation::stateless_temporality_selector(),
                 )
                 .with_memory(true),