Add lean_attestation_committee_count Prometheus metric

bin/ethlambda/src/main.rs

@@ -84,6 +84,9 @@ async fn main() -> eyre::Result<()> {
     // Set node info metrics
     ethlambda_blockchain::metrics::set_node_info("ethlambda", version::CLIENT_VERSION);
     ethlambda_blockchain::metrics::set_node_start_time();
+    ethlambda_blockchain::metrics::set_attestation_committee_count(
+        options.attestation_committee_count,
+    );
 
     let api_socket = SocketAddr::new(options.http_address, options.api_port);
     let metrics_socket = SocketAddr::new(options.http_address, options.metrics_port);

crates/blockchain/src/metrics.rs

@@ -358,6 +358,19 @@ pub fn set_is_aggregator(is_aggregator: bool) {
     LEAN_IS_AGGREGATOR.set(i64::from(is_aggregator));
 }
 
+/// Set the attestation committee count gauge.
+pub fn set_attestation_committee_count(count: u64) {
+    static LEAN_ATTESTATION_COMMITTEE_COUNT: std::sync::LazyLock<IntGauge> =
+        std::sync::LazyLock::new(|| {
+            register_int_gauge!(
+                "lean_attestation_committee_count",
+                "Number of attestation committees (ATTESTATION_COMMITTEE_COUNT)"
+            )
+            .unwrap()
+        });
+    LEAN_ATTESTATION_COMMITTEE_COUNT.set(count.try_into().unwrap_or_default());
+}
+
 /// Observe the depth of a fork choice reorg.
 pub fn observe_fork_choice_reorg_depth(depth: u64) {
     static LEAN_FORK_CHOICE_REORG_DEPTH: std::sync::LazyLock<Histogram> =

docs/metrics.md

@@ -73,6 +73,7 @@ The exposed metrics follow [the leanMetrics specification](https://github.com/le
 
 | Name   | Type  | Usage | Sample collection event | Labels | Supported |
 |--------|-------|-------|-------------------------|--------|-----------|
+|`lean_attestation_committee_count`| Gauge | Number of attestation committees | On node start | | ✅ |
 |`lean_connected_peers`| Gauge | Number of connected peers | On scrape | client=ethlambda,grandine,lantern,lighthouse,qlean,ream,zeam | ✅(*) |
 |`lean_peer_connection_events_total`| Counter | Total number of peer connection events | On peer connection | direction=inbound,outbound<br>result=success,timeout,error | ✅ |
 |`lean_peer_disconnection_events_total`| Counter | Total number of peer disconnection events | On peer disconnection | direction=inbound,outbound<br>reason=timeout,remote_close,local_close,error | ✅ |