From a7fcdd4778730563e4657e90262dadddebefeb60 Mon Sep 17 00:00:00 2001
From: Sze Ching <teo.ching@diamond.ac.uk>
Date: Wed, 28 Jan 2026 17:50:22 +0000
Subject: [PATCH] feat(graph-proxy): add request duration as observable metrics

---
 backend/graph-proxy/src/graphql/mod.rs | 26 ++++++++++++++++++++++++--
 backend/graph-proxy/src/metrics.rs     | 15 +++++++++++++--
 2 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/backend/graph-proxy/src/graphql/mod.rs b/backend/graph-proxy/src/graphql/mod.rs
index 76f97543a..1806c5042 100644
--- a/backend/graph-proxy/src/graphql/mod.rs
+++ b/backend/graph-proxy/src/graphql/mod.rs
@@ -116,7 +116,9 @@ pub async fn graphql_handler(
     auth_token_header: Option<TypedHeader<Authorization<Bearer>>>,
     request: GraphQLRequest,
 ) -> GraphQLResponse {
+    let start = std::time::Instant::now();
     let query = request.into_inner();
+    let mut request_type = "unparseable";
 
     if let Ok(query) = parse_query(&query.query) {
         let operation = query.operations;
@@ -130,19 +132,24 @@ pub async fn graphql_handler(
                 .map(|operation| operation.1.node.ty)
                 .collect(),
         };
+        let mut has_mutation = false;
         for operation in operations {
             match operation {
                 async_graphql::parser::types::OperationType::Query => state
                     .metrics_state
                     .total_requests
                     .add(1, &[KeyValue::new("request_type", "query")]),
-                async_graphql::parser::types::OperationType::Mutation => state
+                async_graphql::parser::types::OperationType::Mutation => {
+                    has_mutation = true;
+                    state
                     .metrics_state
                     .total_requests
-                    .add(1, &[KeyValue::new("request_type", "mutation")]),
+                    .add(1, &[KeyValue::new("request_type", "mutation")])
+                },
                 async_graphql::parser::types::OperationType::Subscription => {}
             };
         }
+        request_type = if has_mutation { "mutation" } else { "query" };
     } else {
         state
             .metrics_state
@@ -152,6 +159,21 @@ pub async fn graphql_handler(
 
     let auth_token = auth_token_header.map(|header| header.0);
     state.schema.execute(query.data(auth_token)).await.into()
+    let response = state.schema.execute(query.data(auth_token)).await;
+    let elapsed_ms = start.elapsed().as_secs_f64() * 1000.0;
+    let status = if response.errors.is_empty() {
+        "ok"
+    } else {
+        "error"
+    };
+    state.metrics_state.request_duration_ms.record(
+        elapsed_ms,
+        &[
+            KeyValue::new("request_type", request_type),
+            KeyValue::new("status", status),
+        ],
+    );
+    response.into()
 }
 
 lazy_static! {
diff --git a/backend/graph-proxy/src/metrics.rs b/backend/graph-proxy/src/metrics.rs
index e61ed555f..458fc38d7 100644
--- a/backend/graph-proxy/src/metrics.rs
+++ b/backend/graph-proxy/src/metrics.rs
@@ -1,6 +1,6 @@
 use std::sync::Arc;
 
-use opentelemetry::metrics::{Counter, MeterProvider};
+use opentelemetry::metrics::{Counter, Histogram, MeterProvider};
 use opentelemetry_sdk::metrics::SdkMeterProvider;
 
 /// Thread-safe wrapper for OTEL metrics
@@ -11,6 +11,8 @@ pub type MetricsState = Arc<Metrics>;
 pub struct Metrics {
     /// Total requests on all routes
     pub total_requests: Counter<u64>,
+    /// Request duration in miliseconds on every request
+    pub request_duration_ms: Histogram<f64>,
 }
 
 impl Metrics {
@@ -23,6 +25,15 @@ impl Metrics {
             .with_description("The total requests on all routes made since the last restart.")
             .build();
 
-        Metrics { total_requests }
+        let request_duration_ms = meter
+            .f64_histogram("graph_proxy_request_duration_ms")
+            .with_description("GraphQL request duration")
+            .with_unit("ms")
+            .build();
+
+        Metrics {
+            total_requests,
+            request_duration_ms,
+        }
     }
 }