add RELAY_LAST_SLOT metric

crates/pbs/src/metrics.rs

@@ -5,8 +5,8 @@
 
 use lazy_static::lazy_static;
 use prometheus::{
-    register_histogram_vec_with_registry, register_int_counter_vec_with_registry, HistogramVec,
-    IntCounterVec, Registry,
+    register_histogram_vec_with_registry, register_int_counter_vec_with_registry,
+    register_int_gauge_vec_with_registry, HistogramVec, IntCounterVec, IntGaugeVec, Registry,
 };
 
 lazy_static! {
@@ -32,6 +32,15 @@ lazy_static! {
     )
     .unwrap();
 
+    /// Latest slot for which relay delivered a header
+    pub static ref RELAY_LAST_SLOT: IntGaugeVec = register_int_gauge_vec_with_registry!(
+        "relay_last_slot",
+        "Latest slot for which relay delivered a header",
+        &["relay_id"],
+        PBS_METRICS_REGISTRY
+    )
+    .unwrap();
+
     // TO BEACON NODE
     /// Status code returned to beacon node by endpoint
     pub static ref BEACON_NODE_STATUS: IntCounterVec = register_int_counter_vec_with_registry!(

crates/pbs/src/mev_boost/get_header.rs

@@ -25,7 +25,7 @@ use url::Url;
 
 use crate::{
     constants::{GET_HEADER_ENDPOINT_TAG, TIMEOUT_ERROR_CODE, TIMEOUT_ERROR_CODE_STR},
-    metrics::{RELAY_LATENCY, RELAY_STATUS_CODE},
+    metrics::{RELAY_LAST_SLOT, RELAY_LATENCY, RELAY_STATUS_CODE},
     state::{BuilderApiState, PbsState},
 };
 
@@ -79,7 +79,10 @@ pub async fn get_header<S: BuilderApiState>(
         let relay_id = relays[i].id.as_ref();
 
         match res {
-            Ok(Some(res)) => relay_bids.push(res),
+            Ok(Some(res)) => {
+                RELAY_LAST_SLOT.with_label_values(&[relay_id]).set(params.slot as i64);
+                relay_bids.push(res)
+            }
             Ok(_) => {}
             Err(err) if err.is_timeout() => error!(err = "Timed Out", relay_id),
             Err(err) => error!(?err, relay_id),