Have more tags in the in_flight_requests meter (eg "service")

The host tag is not currently included, but could be added later with some refactorings if we need it.
add small comment
2024-05-01 11:43:11 +02:00 · 2024-04-26 13:11:25 +02:00
1 changed files with 18 additions and 13 deletions
--- a/src/https.rs
+++ b/src/https.rs
@ -45,12 +45,12 @@ struct HttpsMetrics {
 	request_proxy_duration: metrics::Histogram<f64>,
 }

-struct InFlightGuard<'a> {
-	metrics: Arc<HttpsMetrics>,
-	tags: &'a [KeyValue],
+struct InFlightGuard<'a, 'b> {
+	metrics: &'a HttpsMetrics,
+	tags: &'b [KeyValue],
 }

-impl<'a> Drop for InFlightGuard<'a> {
+impl<'a, 'b> Drop for InFlightGuard<'a, 'b> {
 	fn drop(&mut self) {
 		self.metrics.requests_in_flight.add(-1, self.tags)
 	}
@ -179,8 +179,8 @@ async fn handle_request(
 ) -> Result<Response<Body>, Infallible> {
 	let method_tag = KeyValue::new("method", req.method().to_string());

-	// The host tag is only included in the requests_received and requests_in_flight
-	// metrics, as for other metrics it can easily lead to cardinality explosions.
+	// The host tag is only included in the requests_received metric,
+	// as for other metrics it can easily lead to cardinality explosions.
 	let host_tag = KeyValue::new(
 		"host",
 		req.uri()
@ -194,13 +194,7 @@ async fn handle_request(
 			.unwrap_or_default(),
 	);

-	let tags = [host_tag, method_tag.clone()];
-	metrics.requests_received.add(1, &tags);
-	metrics.requests_in_flight.add(1, &tags);
-	let _guard = InFlightGuard {
-		metrics: Arc::clone(&metrics),
-		tags: &tags,
-	};
+	metrics.requests_received.add(1, &[host_tag, method_tag.clone()]);

 	let mut tags = vec![method_tag];
 	let resp = select_target_and_proxy(
@ -292,6 +286,17 @@ async fn select_target_and_proxy(
 		);
 		proxy_to.calls_in_progress.fetch_add(1, Ordering::SeqCst);

+		let tags_in_flight = &tags.clone();
+		metrics.requests_in_flight.add(1, &tags_in_flight);
+		// The guard ensures that we decrement requests_in_flight in all cases where
+		// the current tasks ends, including the case where it gets canceled and
+		// doesn't run to completion (which may happen e.g. if it timeouts).
+		// (Crucially we create the guard before the first .await in this function.)
+		let _guard = InFlightGuard {
+			metrics: &metrics,
+			tags: &tags_in_flight,
+		};
+
 		// Forward to backend
 		debug!("{}{} -> {}", host, path, proxy_to);
 		trace!("Request: {:?}", req);
Author	SHA1	Message	Date
Armaël Guéneau	2999e366d8	Have more tags in the in_flight_requests meter (eg "service") The host tag is not currently included, but could be added later with some refactorings if we need it.	2024-05-01 11:43:11 +02:00
Armaël Guéneau	1f621cd2a5	add small comment	2024-04-26 13:11:25 +02:00