feat(ml-service): add Prometheus metrics and request telemetry instrumentation

apps/ml-service/src/telemetry.rs

@@ -0,0 +1,118 @@
+use prometheus::{Counter, Gauge, Histogram, HistogramOpts, Registry, TextEncoder};
+use std::sync::OnceLock;
+use std::time::Instant;
+
+fn global_registry() -> &'static Registry {
+    static REGISTRY: OnceLock<Registry> = OnceLock::new();
+    REGISTRY.get_or_init(|| {
+        Registry::new_custom(Some("zeavis_ml".to_string()), None).expect("create registry")
+    })
+}
+
+macro_rules! define_metric {
+    ($name:ident, $ty:ty, $init:expr) => {
+        pub fn $name() -> &'static $ty {
+            static METRIC: OnceLock<$ty> = OnceLock::new();
+            METRIC.get_or_init(|| {
+                let m = $init;
+                global_registry()
+                    .register(Box::new(m.clone()))
+                    .expect(concat!("register ", stringify!($name)));
+                m
+            })
+        }
+    };
+}
+
+// ── HTTP Metrics ────────────────────────────────────────
+
+define_metric!(
+    http_requests_total,
+    Counter,
+    Counter::new("zeavis_ml_http_requests_total", "Total number of HTTP requests")
+        .expect("create counter")
+);
+
+define_metric!(
+    http_request_duration_seconds,
+    Histogram,
+    Histogram::with_opts(
+        HistogramOpts::new(
+            "zeavis_ml_http_request_duration_seconds",
+            "HTTP request duration in seconds",
+        )
+        .buckets(vec![0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0]),
+    )
+    .expect("create histogram")
+);
+
+define_metric!(
+    http_requests_active,
+    Gauge,
+    Gauge::new(
+        "zeavis_ml_http_requests_active",
+        "Number of active HTTP requests",
+    )
+    .expect("create gauge")
+);
+
+// ── Business Metrics ────────────────────────────────────
+
+define_metric!(
+    predictions_total,
+    Counter,
+    Counter::new(
+        "zeavis_ml_predictions_total",
+        "Total number of prediction requests",
+    )
+    .expect("create counter")
+);
+
+define_metric!(
+    model_load_status,
+    Gauge,
+    Gauge::new(
+        "zeavis_ml_model_load_status",
+        "Model load status (1 = loaded, 0 = not loaded)",
+    )
+    .expect("create gauge")
+);
+
+// ── Request Guard (Drop-based cleanup for active gauge) ─
+
+pub struct RequestMetricsGuard {
+    start: Instant,
+}
+
+impl RequestMetricsGuard {
+    pub fn new() -> Self {
+        http_requests_active().inc();
+        Self {
+            start: Instant::now(),
+        }
+    }
+
+    /// Record duration and request count before the guard drops.
+    pub fn finish(&self) {
+        http_request_duration_seconds().observe(self.start.elapsed().as_secs_f64());
+        http_requests_total().inc();
+    }
+}
+
+impl Drop for RequestMetricsGuard {
+    fn drop(&mut self) {
+        http_requests_active().dec();
+    }
+}
+
+// ── Export ──────────────────────────────────────────────
+
+pub fn encode_metrics() -> String {
+    let encoder = TextEncoder::new();
+    let mut buffer = String::new();
+    let metric_families = global_registry().gather();
+    encoder
+        .encode_utf8(&metric_families, &mut buffer)
+        .unwrap();
+    buffer
+}