Remove deprecated apollo.router.session.count.active metric

.changesets/breaking_zach_router_1765_remove_session_count_active.md

@@ -0,0 +1,7 @@
+### Remove deprecated `apollo.router.session.count.active` metric
+
+The `apollo.router.session.count.active` up/down counter — deprecated throughout 2.x — has been removed. It measured the number of in-flight GraphQL requests, duplicating the OpenTelemetry-compliant `http.server.active_requests` metric and causing confusion in dashboards that displayed both.
+
+If your dashboards or alerts reference `apollo.router.session.count.active` (exported as `apollo_router_session_count_active` in Prometheus), switch to [`http.server.active_requests`](https://www.apollographql.com/docs/graphos/routing/observability/router-telemetry-otel/enabling-telemetry/instruments#opentelemetry-standard-instruments), which follows OpenTelemetry semantic conventions and measures the same value.
+
+By [@BobaFetters](https://github.com/BobaFetters) in https://github.com/apollographql/router/pull/ROUTER-1765

apollo-router/src/axum_factory/axum_http_server_factory.rs

@@ -200,13 +200,6 @@ impl HttpServerFactory for AxumHttpServerFactory {
                 configuration.supergraph.path
             );
 
-            tracing::warn!(
-                "The `apollo.router.session.count.active` metric is deprecated and may be \
-                 removed in a future release. Switch to the OpenTelemetry-compliant \
-                 `http.server.active_requests` metric instead. See \
-                 https://www.apollographql.com/docs/graphos/routing/observability/router-telemetry-otel/enabling-telemetry/standard-instruments#session"
-            );
-
             // serve extra routers
 
             let listeners_and_routers =
@@ -407,13 +400,6 @@ async fn handle_graphql<RF: RouterFactory>(
     Extension(service_factory): Extension<RF>,
     http_request: Request<axum::body::Body>,
 ) -> impl IntoResponse {
-    let _guard = i64_up_down_counter_with_unit!(
-        "apollo.router.session.count.active",
-        "Amount of in-flight sessions (deprecated, use `http.server.active_requests` instead)",
-        "{session}",
-        1
-    );
-
     let HandlerOptions {
         early_cancel,
         experimental_log_on_broken_pipe,

docs/source/routing/observability/router-telemetry-otel/enabling-telemetry/standard-instruments.mdx

@@ -88,16 +88,6 @@ You can attach custom attributes using [router selectors](/router/configuration/
 - `apollo.router.graphql_error` - counts GraphQL errors in responses. Also counts errors which occur during the response validation phase, which are represented in client responses as `extensions.valueCompletion` instead of actual GraphQL errors. Attributes:
   - `code`: error code, including `RESPONSE_VALIDATION_FAILED` in the case of a value completion error.
 
-## Session
-
-- `apollo.router.session.count.active` - Number of in-flight GraphQL requests. **Deprecated**: use `http.server.active_requests` instead.
-
-<Note>
-
-`apollo.router.session.count.active` is a legacy Apollo-specific metric. Apollo recommends using [`http.server.active_requests`](/graphos/routing/observability/router-telemetry-otel/enabling-telemetry/instruments#opentelemetry-standard-instruments) instead, which follows OpenTelemetry semantic conventions and is the standard way to measure in-flight HTTP requests. `apollo.router.session.count.active` might be removed in a future release.
-
-</Note>
-
 ## Cache
 
 - `apollo.router.cache.size` — Number of entries in the cache

examples/telemetry/metric-rename.router.yaml

@@ -48,10 +48,10 @@ telemetry:
             # Only these attributes will be preserved on the renamed metric
 
           # Example 5: Rename with custom description and unit
-          - name: apollo.router.session.count.active
-            rename: custom.active.sessions
-            description: "Number of active GraphQL sessions"
-            unit: "{session}"
+          - name: apollo.router.opened.subscriptions
+            rename: custom.active.subscriptions
+            description: "Number of currently open subscriptions"
+            unit: "{subscription}"
 
       # OTLP exporter - receives renamed metrics
       otlp: