add small comment

Add a metrics counter measuring in-flight requests
2024-04-26 13:12:04 +02:00 · 2024-04-26 13:12:04 +02:00
1 changed files with 29 additions and 5 deletions
--- a/src/https.rs
+++ b/src/https.rs
@ -41,9 +41,21 @@ pub struct HttpsConfig {
 struct HttpsMetrics {
 	requests_received: metrics::Counter<u64>,
 	requests_served: metrics::Counter<u64>,
+	requests_in_flight: metrics::UpDownCounter<i64>,
 	request_proxy_duration: metrics::Histogram<f64>,
 }

+struct InFlightGuard<'a> {
+	metrics: Arc<HttpsMetrics>,
+	tags: &'a [KeyValue],
+}
+
+impl<'a> Drop for InFlightGuard<'a> {
+	fn drop(&mut self) {
+		self.metrics.requests_in_flight.add(-1, self.tags)
+	}
+}
+
 pub async fn serve_https(
 	config: HttpsConfig,
 	cert_store: Arc<CertStore>,
@ -62,6 +74,10 @@ pub async fn serve_https(
 			.u64_counter("https_requests_served")
 			.with_description("Total number of requests served over HTTPS")
 			.init(),
+		requests_in_flight: meter
+			.i64_up_down_counter("https_requests_in_flight")
+			.with_description("Current number of requests handled over HTTPS")
+			.init(),
 		request_proxy_duration: meter
 			.f64_histogram("https_request_proxy_duration")
 			.with_description("Duration between time when request was received, and time when backend returned status code and headers")
@ -163,8 +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 metric,
-	// as for other metrics it can easily lead to cardinality explosions.
+	// 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.
 	let host_tag = KeyValue::new(
 		"host",
 		req.uri()
@ -178,9 +194,17 @@ async fn handle_request(
 			.unwrap_or_default(),
 	);

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

 	let mut tags = vec![method_tag];
 	let resp = select_target_and_proxy(
Author	SHA1	Message	Date
Armaël Guéneau	1642b6efc4	add small comment	2024-04-26 13:12:04 +02:00
Armaël Guéneau	2f7b5379ff	Add a metrics counter measuring in-flight requests	2024-04-26 13:12:04 +02:00