dekaf: Expose more useful api histogram buckets

Cargo.toml

@@ -86,7 +86,7 @@ lz4_flex = "0.11.0"
 mime = "0.3"
 memchr = "2.5"
 metrics = "0.23.0"
-metrics-prometheus = "0.7.0"
+metrics-exporter-prometheus = "0.15.3"
 prometheus = "0.13.4"
 md5 = "0.7.0"
 num-bigint = "0.4"

crates/dekaf/Cargo.toml

@@ -40,7 +40,7 @@ kafka-protocol = { workspace = true }
 lz4_flex = { workspace = true }
 md5 = { workspace = true }
 metrics = { workspace = true }
-metrics-prometheus = { workspace = true }
+metrics-exporter-prometheus = { workspace = true }
 percent-encoding = { workspace = true }
 postgrest = { workspace = true }
 prometheus = { workspace = true }

crates/dekaf/src/lib.rs

@@ -302,7 +302,7 @@ async fn handle_api(
     let handle_duration = SystemTime::now().duration_since(start_time)?;
 
     metrics::histogram!("api_call_time", "api_key" => format!("{:?}",api_key))
-        .record(handle_duration.as_millis() as f64);
+        .record(handle_duration.as_secs_f32() as f64);
 
     ret
 }

crates/dekaf/src/main.rs

@@ -105,8 +105,6 @@ async fn main() -> anyhow::Result<()> {
         .with_writer(std::io::stderr)
         .init();
 
-    metrics_prometheus::install();
-
     let cli = Cli::parse();
     tracing::info!("Starting dekaf");
 
@@ -163,7 +161,7 @@ async fn main() -> anyhow::Result<()> {
         .await
         .context("failed to bind server port")?;
 
-    let metrics_router = dekaf::metrics_server::build_router(app.clone());
+    let metrics_router = dekaf::metrics_server::build_router();
     let metrics_server_task =
         axum_server::bind(metrics_addr).serve(metrics_router.into_make_service());
     tokio::spawn(async move { metrics_server_task.await.unwrap() });

crates/dekaf/src/metrics_server.rs

@@ -1,13 +1,21 @@
-use super::App;
-use std::sync::Arc;
+use metrics_exporter_prometheus::{PrometheusBuilder, PrometheusHandle};
 
-pub fn build_router(app: Arc<App>) -> axum::Router<()> {
+pub fn build_router() -> axum::Router<()> {
     use axum::routing::get;
 
+    let prom = PrometheusBuilder::new()
+        .set_buckets(
+            &prometheus::exponential_buckets(0.00001, 2.5, 15)
+                .expect("calculating histogram buckets"),
+        )
+        .expect("calculating histogram buckets")
+        .install_recorder()
+        .expect("failed to install prometheus recorder");
+
     let schema_router = axum::Router::new()
         .route("/metrics", get(prometheus_metrics))
         .layer(tower_http::trace::TraceLayer::new_for_http())
-        .with_state(app);
+        .with_state(prom);
 
     schema_router
 }
@@ -23,12 +31,10 @@ fn record_jemalloc_stats() {
 }
 
 #[tracing::instrument(skip_all)]
-async fn prometheus_metrics() -> (axum::http::StatusCode, String) {
+async fn prometheus_metrics(
+    axum::extract::State(prom_handle): axum::extract::State<PrometheusHandle>,
+) -> (axum::http::StatusCode, String) {
     record_jemalloc_stats();
 
-    match prometheus::TextEncoder::new().encode_to_string(&prometheus::default_registry().gather())
-    {
-        Err(e) => (axum::http::StatusCode::INTERNAL_SERVER_ERROR, e.to_string()),
-        Ok(result) => (axum::http::StatusCode::OK, result),
-    }
+    (axum::http::StatusCode::OK, prom_handle.render())
 }